Title Page
 Table of Contents
 List of figures
 List of tables
 Summary and recommendations
 Literature cited

Title: Emergy analysis and policy perspectives for the Sea of Cortez, Mexico
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Permanent Link: http://ufdc.ufl.edu/UF00016670/00001
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Title: Emergy analysis and policy perspectives for the Sea of Cortez, Mexico
Physical Description: Book
Language: English
Creator: Brown, Mark T.
Tennenbaum, Stephenh
Odum, H. T.
Publisher: Center for Wetlands, University of Florida
Publication Date: 1991
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Volume ID: VID00001
Source Institution: University of Florida
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Resource Identifier: notis - AAA9287

Table of Contents
    Title Page
        Title Page
    Table of Contents
        Page i
    List of figures
        Page ii
    List of tables
        Page iii
        Page iv
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    Summary and recommendations
        Page 43
        Page 44
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    Literature cited
        Page 56
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        Page 58
Full Text

Report to


Emergy Analysis and Policy Perspectives

for the Sea of Cortez, Mexico

Mark T. Brown, Stephen Tennenbaum, and H. T. Odum

CFW Publication # 88-04

Research Studies Conducted under Contract No. 571945612
to The Cousteau Society

Center for Wetlands
University of Florida
Phelps Lab
Gainesville, Florida 32611

May 1991


LIST OF FIGURES ..................... .................................... ii

LIST OF TABLES ....................................................... iii

PREFACE ............................................................ iv

INTRODUCTION ...................... ............ ...................... 1
Public Policy: The Interface of Ecology and Economics ................ .......... 1
Scope of the Study .................... .............................. 4
The Northern Sea of Cortez .................. .. .. ....................... 5

METHODS ...................................... ...................... 9
The Maximum Emergy Principle ............. ............................ 9
Em ergy .................................................... 11
Transformity .. ........................................ 11

RESULTS .......................................... ...................... 13
National Emergy Table ..................... ....................... 13
Overview Systems Diagram ....................................... 13
Water Budget and the Sea ........................................ 13
EMERGY Tables for the Sea of Cortez ............. .............. 18
Primary Production by Photoplankton and its EMERGY Evaluation .............. 18
Fishing and Its EMERGY Evaluation ................................. 18

DISCUSSION ............................................................ 31
The Effect of the Colorado River Diversion ..................................... 31
EMERGY Budget ............................................... 31
Budgets of Water, Organic Matter, and nutrients ................. ......... 32
Fresh W after ................................................. 32
Organic Matter ................... ............................ 32
Nutrients ................... ................................ 33
Summ ary ................................................... 33
Primary Production .................... ............................. 34
Fisheries in the Sea of Cortez ...................................... ...... 35
The Sea of Cortez and the Economy of Mexico ................................. 39
Local Use of Fisheries Versus Export Sales ..................................... 40

SUMMARY AND RECOMMENDATIONS .......................................... 43

APPENDIX ............... ............................................45

LITERATURE CITED ................. ................................... 56


Number Page

1 Map of the Sea of Cortez showing the northern study area. ....................... 2

2 Discharge of the Colorado River below Hoover Dam (from McCleary, 1986). ........... 3

3 Map of the northern Sea of Cortez showing upwelling areas and areas above the 200
meter depth (after Roden: 1958, 1964). ...................................... 7

4 Energy language symbols ................ ........................... 10

5 Diagram illustrating the methodology for calculating EMERGY and transformity .......... 12

6 Energy systems diagram of the Sea of Cortez. .............................. 15

7 Total storage and annual flows of water (top) and organic matter (bottom) in the
Sea of Cortez in the 1920s ............................................ 16

8 Total storage and annual flows of phosphorus as PO4 (top) and nitrogen as NO3
(bottom) in the Sea of Cortez in the 1920s ................................ 17

9 Average annual EMERGY inflowing to the Sea of Cortez for the 1920s, 1960s, and 1980s. 24

10 Average annual EMERGY inflowing to primary production in the Sea of Cortez for
the 1920s, 1960s, and 1980s ........................................... 25

11 The number of new fishing boats commissioned each year that are still fishing (top)
and cumulative number of boats (bottom). ................................. 26

12 Summary diagram of the Sea of Cortez shrimp fishery. ......................... 27

13 Summary diagrams of EMERGY and dollar flows for the large boat shrimp fishery
and pangas shrimp fishery in the Sea of Cortez. .............................. 30

14 Diagram summarizing the investment ratio for the large boat shrimp fishery in
the Sea of Cortez ................ ...................... ........... 38

15 Net benefits resulting from the sale of shrimp. .............................. 42


Number Page

1 Emergy Evaluation of resource basis for Mexico in 1983 (from Odum et al., 1987) ......... 14

2 Emergy flows of the Sea of Cortez (1920s). ................................. 19

3 Emergy flows of the Sea of Cortez (1960s). ................................ 20

4 Emergy flows of the Sea of Cortez (1980s). ................................. 21

5 Emergy flows of primary productivity (1960s). ............................... 23

6 Emergy costs and shrimp yield per year: Shrimp Trawlers. ...................... 28

7 Emergy costs and shrimp yield per year: Small Boats (Pangas). ................... 29


Among the most important problems humanity faces today are the sound management of natural resources
and the integration of human and natural processes. There is a need to understand both human and natural
domains, each in the context of the other, and it is important to develop management strategies which
acknowledge and promote the vital interconnections between the two.
Traditionally, a reductionist approach to the study of humanity and nature has been taken. By comparison,
very little attention has been given to studying the biosphere at the ecosystem level of organization. It is at the
ecosystem level, however, where many of nature's benefits are derived and where the impacts of humanity are
being felt.
Neither economics nor ecology alone adequately address the problems society presently faces: a unifying
concept or common denominator is needed which embodies both the natural and human domains. Energy flows
through and is stored by both systems. Evaluating energy flow, energy quality and embodied energy enables
one to quantify and compare various resource uses and to determine which development strategies maximize the
energetic of both human and natural systems. The appropriate use will be the one which maximizes the flow
and storage of energy for both humanity and nature.
In the Sea of Cortez, it is the upper Gulf where the great forces of nature combine to nurture both nature
and humanity. The Colorado River carries sediments and nutrients from the continental heartland to fertilize the
upper Gulf. In addition, it is here where tides and upwelling make their contribution, creating the highest rates
of productivity found in the Sea of Cortez. This productivity is responsible for Mexico's most important
fishery, providing both food and economic benefit to society.
In view of the importance of the upper Gulf region to the entire Sea of Cortez, we have invited Dr. H. T.
Odum and his team to employ their energy analysis techniques to study this region in conjunction with the
Cousteau Sea of Cortez Expedition. The objective of The Cousteau Society is to educate and to communicate
on a global scale so as to protect and improve the quality of life for present and future generations. We hope
the Odum methods, and the contents of this document, will provide some interesting insights about important
processes in the Gulf and will help foster better resource management for the future.

Richard C. Murphy
Vice President for Science and Education
The Cousteau Society


Valuable, unique, and important to the local economies, the Sea of Cortez in Northwestern Mexico
(Figure 1) is becoming increasingly joined to the main economy of Mexico and the United States. As a
microcosm of international resource use in developing countries, the Sea of Cortez provides an example for
application of new methods for determining public policies that maximize sustainable economies symbiotic with
the sea. In this study, emergy analysis (spelled with an "M") is used to facilitate the process that may
determine which future alternatives maximize public benefit.
Originally, the Colorado River had strong flow into the upper end of the Sea; but starting in 1935, water
was diverted, with some flow restored in 1940 and 1984. Figure 2 shows the large changes in the discharge in
this century. More recently, there has been expansion of fisheries with larger shrimp trawlers and international
markets replacing local fishermen with local markets. In this study emergy analyses are made to evaluate the
importance of the changes in the past and anticipated in the future.

Public Policy: The Interface of Ecology and Economics.

The interface of ecology and economics is often in the marketplace where resources are exploited and
sold. In the process, the environment sustains some transformations that may or may not lead to long-term
stability. As the population expands, it is increasingly important that humans consider the long-term
environmental consequences of their economic decisions. A long-term perspective and macroscopic view are
needed in order to adequately factor in questions of long-term sustainability in our public policy decision
Too often, economics, with its short time horizon and its small, closed value system, is the guiding
rationale behind public policy decisions. Its value system is small by virtue of the fact that it considers utility as
the means for determining value, and it is closed because it does not extend beyond the marketplace. Thus,
public policy decisions made under the assumption of maximizing some monetary value (increased sales, profits,
marginal rate of return) are, in reality, basing the decision on individual human utility. Societal needs or
environmental concerns are often not factored in because they are generally outside the realm of individual
human preferences.

Figure 1. Map of the Sea of Cortez showing the northern study area.


1906 ftUJ 1964 SEGINS LAKE WA-0


1905 1915 195 1 9
1905 1915 1925 1935 1945






Discharge of the Colorado River below Hoover Dam (from McCleary 1986).

Figure 2.

JE 1980 LAM




Public policy decisions need to be made on the basis of the value system of the Earth. The new public
policy value system used here recognizes the difference between short-term individual human preference and
long-term macroscopic well-being and is capable of quantitatively determining value at the macroscopic scale of
society and environment. It can equate the value of natural resources, wildlife, and industrial production as a
means of determining relative importance and their contributions to overall well-being and long-term
sustainability. The system of evaluation used in this report measures value in units of emergy, a relatively new
concept, that measures the resources required for a product. Emergy is expressed in units of Solar EmJoules
(sej) as a means of expressing the values of diverse products like fishing boats and shrimp on an equivalent
scale. In a nutshell, the best system and the one which is eventually successful is one that uses the most
The emergy system of value is based on concepts of system organization and optimization that have their
bases in the early work of Lotka (1922a, 1922b, 1945), in General System Theory (von Bertalanffy, 1968), and
in Systems Ecology (Odum, 1983). As a result of its foundations in ecology and general system theory, the
conceptual framework for an Emergy Theory of Value has longer time horizons and applicability than
marketplace economics.

Scope of the Study

As part of The Cousteau Sea of Cortez Expedition, the authors were invited to focus their attention on
resource management policy questions facing the people of the United States and Mexico. The productivity of
the Sea of Cortez is an important yet little recognized contribution to the economy of Mexico. Local economies
are sustained by productive near-shore fisheries, and increasingly the Mexican national economy has been
boosted by a highly capitalized export shrimp fishery. Combined, these contributions of natural productivity act
to stimulate the economy as the money that is received from exports of shrimp and local sales of fish ripple
through the economy "demanding" further exchanges and resource utilization.
While traditional economic "wisdom" would suggest that increasing exports and general exploitation of the
Sea of Cortez fishery are to be desired as a means of offsetting a balance of payments deficit and heavy external
debt, such economic advice does not consider that the resource base is limited and that overexploitation now
may lead to a collapse later. An additional concern is related to the relative value of exported products versus
the value of goods received in exchange. Balance of payments measured in dollars and those measured in
emergy are two distinctly different concepts and arrive at two distinctly different values. The former is a
measure of value to humans, the latter is a measure of value as a contribution to the economy as a whole. The

different value systems lead to differing points of view regarding public policy issues and often to opposing
solutions to questions of resource management.
Using techniques of emergy analysis that equate the work done in the human domain with work done in
domains considered to be outside the human economy, this study evaluates the relative importance of the Sea of
Cortez to the economy of Mexico, the possible impact of Colorado River diversions, alternative methods of
shrimp fishing, and the equity of foreign trade involving fishery products.

The Northern Sea of Cortez

The Sea of Cortez (also known as the Gulf of California) lies between the arid Baja California Peninsula
and the equally arid Mexican mainland States of Sinaloa and Sonora (Figure 3). Many have likened it to a large
evaporation basin with a southern opening to the ocean (Roden, 1958, 1964; Alvarez-Borrego, 1983). The Gulf
is about 1000 km long and averages about 150 km wide. At its northern end is the Colorado River Delta.
Along the western shore the Baja coastline is very steep and flanked by numerous islands; while the
northeastern coast (State of Sonora) is less rugged with a wide shelf. Further south, along the Sinaloa coast, the
shoreline is characterized by tidal inlets and mangrove swamps with many streams draining the coastal plain.
The bathymetry of the Gulf is quite varied with a number of basins of varying depths throughout. The
basins and trenches, separated by transverse ridges, deepen from north to south (Byrne and Emery, 1960). The
median depth of the Gulf is about 460 meters, while the deepest basin is over 3300 meters (Shepard, 1950). A
shelf borders most of the Gulf that is widest in the northern portions and narrowest approaching the Pacific. In
contrast to depths of greater than 3000 meters in the southern extreme of the Gulf, the northern third of the
Gulf has depths that average about 250 meters. As shown in Figure 1, the Gulf can be divided by a line
running through the southern tip of Angel de la Guarda Island and the northern tip of Tiburon Island. This line
separates the northern Gulf, which is more estuarine in character (Zeitzschel, 1969), from the middle and
southern Gulf that are more dominated by the Pacific Ocean (Round, 1967). The area north of this line roughly
corresponds to two of the four zones identified by Zeitzschel (1969).
The climate of the Sea of Cortez is more continental than oceanic. The Sea is separated from the Pacific
Ocean by a chain of mountains from 1 to 3 km high running almost the entire length of the Baja Peninsula
greatly reducing the ocean's moderating influence on the climate. Precipitation falls mostly during the summer
in the northern Gulf, varying from traces in the northernmost part to 200 mm per year at Guaymas.
Evaporation is one of the most important factors affecting the Gulf. High surface salinities in the north, where
evaporation far exceeds precipitation, flow south and sink, possibly adding to upwelling through displacement.
Hurricanes may play an important role in both circulation and inputs of rain and runoff carrying sediments.

Wind-driven upwelling is one of the most dominant features of the Gulf (Figure 3). Upwelling is most intense
along the eastern coast of the Baja Peninsula during the winter's northwesterly winds and during the summer's
southeasterly winds along the western coast. Local areas of upwelling are located on the left sides of islands
and headlands (Roden, 1958). General circulation of the Gulf is very complex; however, temperature and
salinity data suggest that the southern Gulf is more thoroughly mixed with the Pacific while the northern Gulf is
somewhat more isolated (Alvarez-Borrego, 1983). Tidal mixing in the north is extensive where mean tidal
range is 6.6 meters (Byrne and Emery, 1960) and spring ranges of 10 meters have been reported
(Alvarez-Borrego, 1983).
Probably of great significance to the northern Gulf is the discharge of the Colorado River. Historically,
average annual discharge was greater than 15 million acre feet (Thompson et al., 1969), transporting an average
of 150 to 200 million tonnes of sediments (McCleary, 1986). In its natural state, the river experienced extreme
flooding events during spring as a result of mountain snowpack melt and minor base flow during the autumn.
Flow varied from spring peaks with daily discharges as high as 250,000 cfs to autumn lows with daily
discharges less than 5000 cfs (Thompson et al., 1969). During the years 1905 to 1907 the entire flow of the
Colorado was diverted to form the present Salton Sea. The flow was rediverted from the Salton Sea following
1907 until the filling of Lake Meade at Hoover Dam. After 1935, with the construction of the Hoover Dam and
other smaller dams along the Colorado, discharge characteristics were greatly altered. Spring peaks were
markedly reduced through the storage in reservoirs and the release of waters over the remainder of the year
(Figure 2). In addition to the discharge characteristics of the river, the dams have also had a major effect on
the Gulf by intercepting sediment loads. While the river used to carry a sediment load of about 180 million
tonnes per year (Thompson, 1965), recent measurements of sediment load by the United States Bureau of
Reclamation show many years within the last decade where the load is less than 100,000 tonnes per year
(McCleary, 1986).
The overall effects of these changes in the discharge characteristics are not well understood. Carlson and
Thompson (1969) speculate that the diminished flow of the Colorado into the Gulf has undoubtedly influenced
the productivity of its headwaters, but conclude since there are no past and present data available, their
speculations have no sound basis. From data collected on three 1968 cruises of the E. B. Scripps, Zeitzschel
(1969) reported average integrated primary productivity for two zones in the northern half of the Gulf of 0.53 g
C/m2 day and 0.677 g C/m2 day and an average integrated rate of primary productivity for all stations within
the Gulf of 0.382 g C/m2 day. He concluded that primary productivity in the Sea of Cortez is comparable to
that in other areas of upwelling like those off the coast of North Africa and in the Bay of Bengal, and that
productivity in the Gulf is two to three times that found in the open Atlantic or Pacific oceans at similar

Puerto Penasco








Figure 3. Map of the northern Sea of Cortez showing upwelling areas and areas of less than 200 meter in
depth (after Roden 1958, 1964).

By considering the potential importance of the Colorado River to the Sea of Cortez and the importance of
the upper Gulf shrimp fishery to Mexico, we have endeavored to address these two subject areas using
techniques of energy analysis. Using existing data in the literature, and limited data collection in the field, we
have attempted to evaluate the importance of the Colorado River to the whole system of the upper Sea of
Cortez. In addition, we use these methods to evaluate the resident shrimp fishery, focusing on differences
between panga (small boat), and trawler fisheries and relating this fishery to Mexico's energy/economic
situation. Finally, we hope this study will serve to introduce the emergy analysis method to the scientists and
resource managers of Mexico and that it may assist them in making important policy decisions fostering
sustainable resource use.


The method of analysis employed in this study provides an overview of the interactions and resource base
of the systems of humanity and nature in the Sea of Cortez. This is accomplished by first gathering as much
relevant information about the complete system as one can find. Then the system is diagrammed using the
energy language symbols illustrated in Figure 4, creating a visual inventory of components and interactions.
Next, aggregate diagrams are created emphasizing the subsystems of interest. Finally, the emergy of the
subsystems (the resource base in terms of equivalent solar input) is calculated so that comparisons can be made
and indices can be calculated to provide perspective on trends and policy.
This study is organized in a hierarchical manner. First, to place the Sea of Cortez in perspective relative
to the overall economy of Mexico, an emergy analysis of the national economy of Mexico is presented. Then,
an emergy analysis of the Sea of Cortez for three different time periods (1920s, 1960s, and 1980s) is presented
to better understand the changes that have occurred as a result of the manipulation of Colorado River discharge;
and finally, emergy analysis of the very productive shrimp fishing that is currently being exploited is presented.
Everything is part of a system and systems are composed of units that are interrelated. As a result of
these interrelationships, it is difficult to understand the functions and values of individual units without first
having a general idea of how all the units fit together to form the whole. We start with the whole economy in
overview. This "top-down" approach facilitates a better understanding of the system and helps to place public
policy issues in a broader perspective. Policy decisions regarding the exploitation of natural resources almost
invariably require the integration of both economic (bigger scale system) and ecologic (smaller scale system)
implications. For instance, resource management decisions regarding the shrimp fishery of the northern Sea of
Cortez, while having local implications on the lives of fishermen and their families and on the sustainability of
the fishery, simultaneously have an impact on the national economy of Mexico and its balance of payments. All
too often policy decisions on the local level are made without sufficient information concerning the implications
at the next larger system level. The reverse is also true; decisions made at the regional or national level have
serious impacts on local economies and resource systems. The hierarchical systems approach presented in the
analysis lends insight and allows for the public policy process to integrate both the economic and ecologic
implication of decisions and management alternatives. There are several terms and concepts that are used in
this report that are not in common usage or that may be unfamiliar to the reader. They are defined next:
The Maximum Emergy Principle: A main principle that offers some clear criteria for how systems are
organized and why some prevail and others do not is the Maximum Emergy Principle.

energy flow from outside the system.

HEAT SINK drains out degraded energy
after its use in work.

delivers energy flow.

ENERGY INTERACTION requires two or
more kinds of energy to produce high quality
energy flow.

flows in exchange for energy.

GENERAL PURPOSE BOX for any sub-unit
needed, is labeled to indicate use.

PRODUCER UNIT converts and
concentrates solar energy, self-maintaining;
details may be shown inside.

CONSUMER UNIT uses high quality energy,
self-maintaining; details may be shown inside.

Figure 4. Energy language symbols.

The Maximum Emergy Principle suggests systems which develop and prevail are those that increase and
take maximum advantage of the energy that is available. Generally, this means that the system organization
which can develop uses for the most energy in the shortest time will displace other patterns that do not use
resources as effectively. Social, economic, and political systems, as well as ecologic systems, prevail in a
competitive environment only if they can develop more emergy inflows and use them more effectively than their
competitors. The pattern that prevails links all its parts in a symbiotic array using all by-products.
Emergy (spelled with an "M"): Emergy in a resource, product, or service is the sum of the solar energies
that are required both directly and indirectly in its production. In this report, all resources, products, and
services are given as solar emergy expressed in solar emjoules. Emjoules are so named to distinguish the units
of emergy from units of energy expression in joules. As and example, Figure 5 shows that the emergy of a fish
sold at market includes the prorated share of emergy spent for goods and services necessary to run and maintain
the fishing vessel, the emergy of the fuel that was burned, the emergy value of goods and services consumed by
the fishermen, and all the emergy from direct sunlight and tidal action that was necessary to provide essential
ecological support for the fish prior to it being caught.
Attempts to evaluate environmental and economic products or services in units of energy must recognize
that all forms of energy do not accomplish equivalent amounts of work. To express the energy value of sunlight
and fuel in joules of heat and then to suggest that each joule is equal in its ability to support work is not
accurate. The "form" or "quality" of each type of energy is quite different and is capable of supporting very
different types of work per unit of energy. To overcome this shortcoming, a measure of work potential based
on solar energy equivalence is used to describe all types of energy as solar emergy.
Transformity: Transformity is the energy of one type required to generate one unit of another type. Its
units are solar emjoules per joule (sej/J). To convert energy of one type to solar energy, units of energy are
multiplied by the SOLAR TRANSFORMITY, converting them to solar emergy equivalents (see Figure 5).
The solar transformity of an object or resource is the equivalent solar energy that would be required to
generate a unit of that object or resource efficiently and rapidly. A solar transformity of a resource is the ratio
of the total amount of solar energy required to create it (solar emergy) to the energy of that resource. It is
obtained by dividing the total solar energy of the system that "creates" the resource by the energy in the
resource output. As an example, the transformity for a fish would be calculated by dividing the solar emergy
required to support the environmental system that "produces" the fish by the energy of the fish (measured as
caloric value) (see Figure 5).

Solar Emergy of Landed Fish

Solar Transformity of Landed Fish
in sej/J

Sum of Emergy of

Solar Emergy of Landed Fish
energy of Landed Fish

Figure 5. Diagram illustrating the methodology for calculating EMERGY and transformity.


The data and calculations upon which this report is based are given in Figures 6 through 13, Tables 1
through 7 and supporting Appendices. The plan was to evaluate the resource base of the national economy of
Mexico and the resource base of the northern Sea of Cortez study area, to investigate the implications of the
Colorado River diversion, and, using emergy analysis, to evaluate the shrimp fishery of the northern Gulf.
National Emergy Table. A cursory evaluation of the overall resource base of the Mexican economy in
1983 is given in energy Table 1. The main inputs to the economy of the country are listed including exports
and imports. The total annual emergy use is given in line 10, which is then used to evaluate an emergy ratio to
the U.S. International Dollar for 1983. Almost 16% of the emergy use was imported goods and services.
Counting the very large oil and gas export (item 8), twice as much emergy was exported as imported.
With a 1983 population of 72 million people, per capital emergy utilization was approximately 5 E15
sej/person. The per capital emergy in the United States in the same year was 34 E15 sej/person. Emergy per
capital is a measure of standard of living. Comparison with the U.S. average suggests that Mexico's standard is
about 1/9 that of the United States.
The ratio of emergy to dollars (a measure of buying power) was 2.86 E12 sej/$ in Mexico, while in the
same year the ratio in the U.S. was 2.4 E12 sej/$ (both expressed in U.S. dollars).
Overview Systems Diagram. The systems diagram in Figure 6 was developed to summarize what items
and relationships are important, based on written papers and local interviews. Items are arranged from left to
right in order of the solar transformity. This means that items on the left are abundant. Those on the right are
less in quantity but more important per unit, requiring more resources and having more controlling effects on
the items to the left. The many energy flows of the Sea of Cortez develop the food chain that ends on the right
in marketable shrimp and fish. The dashed lines on the right are the flows of money at the interface of the
economy with the ecosystem.
Water Budget and the Sea. In order to evaluate components and inflows, budgets were developed for the
Sea of Cortez including water in Figure 7 (top), organic matter in Figure 7 (bottom), phosphate-phosphorus in
Figure 8 (top), and nitrate-nitrogen in Figure 8 (bottom). These are for the period in the 1920s before water
from the Colorado River was diverted. Respectively, Figures 9 and 10, show average annual emergy inflowing
to the sea and to primary production in the sea. At the lower end of the study area marked in Figure 1, a
substantial tide slides water northward and then southward with each tide, about twice a day. This exchange is

Table 1. Emergy Evaluation of the Annual Resource Basis for Mexico in 1983 (from Odum et al., 1987).

Transformity Solar Emergy Value*
Note' Item Raw Units (sej/unit) (E22 sej) (E9 1983 US$)

1 Rain 7.97 E18 J 8888/J 7.1 29.5

2 Tides 3.00 E17 J 23564/J 0.7 2.9

3 Waves 1.37 E18 J 25889/J 3.5 14.7

4 Oil use 2.75 E18 J 53000/J 14.6 60.7

5 Natural gas use 1.39 E18 J 48000/J 6.7 27.8

6 Imported goods &
services 23.1 E9 $ 2.4 E12/$ 5.5 23.1

7 Exported goods &
services 19.3 E9 $ 2.86 E12/$ 5.5 23.0

8 Exported fuels 8.8 36.6

9 Hydroelectricity 2.4 E17 J 4 E4 SEJ/j 1.0 4.0

10 Total input 34.6 144.2

11 Gross Nat'l Product 1.21 Ell $ 2.86 E12/$ 34.6 144.2

sej = Solar equivalent joules
* Solar emergy flow (column 5) divided by 2.4 E12 solar emjoules/$ for U.S. in 1983.

'Refer to numbered notes and calculations given in the appendix.

K Phyto- \/

Dslar rfrmiy. K.. i enrgy, N = nutrnls, S = Serddim ns,
Sun Zoo- fish

S rim Wha

Figure 6. Energy systems diagram of the Sea of Cortez. Items are arranged from right in order of their
solar (ransformity. K.c. = Kinetic energy, N = nutrients, S = sediments, P = price, EVAP.
= evaporation.


Other Runoff

Colorado 18

Tidal Prism 30,464
Exchange 30300



TURNOVER 425days

TURNOVER 425days




Tidal Prism


TURNOVER 410days

FLOWS 1E9gm/yr

Figure 7. Total storage and annual flows of water (top) and organic matter (bottom) in the Sea of Cortez in
the 1980s. Data and calculations are given in the appendix.

Rain -

Other Runoff-

Colorado 2

Tidal Prism 5,2C
Exchange -

FLOWS 1E9gm/yr
STORAGE 1E9gm/yr

TURNOVER 420days

Rain ,

Other Runoff


Tidal Prism


FLOWS 1E9gm/yr



TURNOVER 423days

Figure 8. Total storage and annual flows of phosphorus as PO4 (top) and nitrogen as NO3 (bottom) in the
Sea of Cortez in the 1980s. Data and calculations are given in the appendix.

included in Figures 9 and 10, but most of the water sliding in and out is the same water little changed in the
course of one tidal cycle. The Colorado River brings substantial emergy to the Sea which was much reduced
when the Colorado River was diverted (Figure 9).
EMERGY Tables for the Sea of Cortez. The overview diagram (Figure 6) was used to set up three
emergy analysis tables for the Sea of Cortez for three time periods: Table 2 for the 1920s, Table 3 for the mid
1960s, and Table 4 for the early 1980s. For the calculations, the system was defined by the shaded area in
Figures 1 and 2 and included the entire water column and the part of the bottom sediments involved in regular
biological and chemical processes within the sea. Also included in the tables are economic inputs and outputs.
The tables show which inputs to the sea were large and important. Notice the high values for freshwater
inflows, tidal energy, and goods and services involved in fishing.
Primary Production by Photoplankton and its EMERGY Evaluation. Because of its importance to the
food chains of shrimp and fish, primary production data were assembled and the emergy contribution evaluated
as given in Table 5 and Figure 10. Note the importance of tidal energy and nutrients. The primary production
process is shown in Figure 6 within the system that controls it and supplies its inputs. Figure 10 shows
substantial differences on an emergy basis among the different periods of Colorado River management.
Fishing and EMERGY Evaluation. Data were assembled on fishing efforts for shrimp in the Sea of
Cortez and evaluated for the emergy inflows and yields. The number of boats involved is shown in Figure 11,
which shows a large expansion of the fleet in the 1970s. Figure 12 shows details of the way the food chain of
the Sea is driven and coupled to the fishery harvests.
A comparison was made between the older pattern of small boats and local markets and some newer
shrimp trawlers and international markets. Table 6 has the emergy evaluation based on the inflows and yield of
the larger shrimp trawlers. Table 7 has the emergy analysis of the smaller boats. Figure 13 compares the small
and larger boat systems.

Table 2. Emergy flows of the Sea of Cortez (1920s).

Raw Trans-
Units formity Emergy
Note" Name (units/yr) (sej/unit) E18 sej/yr


Chemical Potential
Kinetic Energy
Organic Matter




Organic Matter

Chemical Potential
Organic Matter
Chemical Potential
Organic Matter


5.60 E20 J

4.90 E16 J
2.88 E14 J
3.80 E14 J
5.95 E8 gm
2.08 E9 gm

6.90 E16 J

4.74 E17 J

3.40 E13 J

2.07 E15 J
6.27 E16 J
4.05 E10 gm
2.63 Ell gm

8.99 E16 J
5.49 E16 J
2.39 E9 gm
3.49 E10 gm

1.91 E16 J
9.15 E15 J
5.07 E8 J
7.14 E9 J

4.24 E13 J

sej = Solar equivalent joules
"Refer to numbered notes and calculations given in the appendix.


1.54 E4
8.89 E3
1.90 E4
1.40 E10
4.19 E9

2.36 E4

6.23 E2

4.10 E4

2.36 E4
1.90 E4
1.40 E10
4.19 E9

4.11 E4
1.90 E4
1.40 E10
4.19 E9

4.11 E4
1.90 E4
1.40 E10
4.19 E9

4.70 E6









Table 3. Emergy flows of the Sea of Cortez (1960s).

Raw Trans-
Units formity Emergy
Note' Name (units/yr) (sej/unit) E18 sej/yr


Chemical Potential
Kinetic Energy
Organic Matter




Organic Matter

Chemical Potential
Organic Matter
Chemical Potential
Organic Matter


5.60 E20 J

4.90 E16 J
2.88 E14 J
3.80 E14 J
5.95 E8 gm
2.08 E9 gm

6.90 E16 J

4.74 E17 J

3.40 E13 J

2.29 E15 J
6.96 E16 J

4.50 E10 gm

2.93 Ell gm

5.50 E14 J
2.14 E12 J
1.50 E7 gm

2.19 E8 gm

1.91 E16 J
9.15 E15 J
5.07 E8 J
7.14 E9 J

4.24 E13 J

sej = Solar equivalent joules
"Refer to numbered notes and calculations given in the appendix.

1.54 E4
8.89 E3
1.90 E4
1.40 E10
4.19 E9

2.36 E4

6.23 E2

4.10 E4

2.36 E4
1.90 E4

1.40 E10
4.19 E9

4.11 E4
1.90 E4
1.40 E10
4.19 E9

4.11 E4
1.90 E4
1.40 E10
4.19 E9

4.70 E6











Table 4. Emergy flows of the Sea of Cortez (1980s).

Raw Trans-
Units formity Emergy
Note" Name (units/yr) (sej/unit) E18 sej/yr

Chemical Potential
Kinetic Energy

Organic Matter
Organic Matter
Chemical Potential

Organic Matter
Chemical Potential
Organic Matter

5.60 E20 J

4.90 E16 J
2.88 E14 J
3.80 E14 J

5.95 E8 gm
2.08 E9 gm
6.90 E16 J
4.74 E17 J
3.40 E13 J

2.22 E15 J
6.58 E16 J
4.25 E10 gm
2.77 Ell gm

3.01 E16 J
1.67 E14 J
8.10 E8 gm
1.18 E10 gm

1.91 E16 J
9.15 E15 J
5.07 E8 J
7.14 E9 J
4.24 E13 J

2.02 E14 J
5.33 E15 J
1.99 E15 J
1.53 E14 J


1.54 E4
8.89 E3

1.90 E4
1.40 E10
4.19 E9
2.36 E4
6.23 E2
4.10 E4

2.36 E4
1.90 E4
1.40 E10
4.19 E9

4.11 E4
1.90 E4
1.40 E10
4.19 E9

4.11 E4
1.90 E4
1.40 E10
4.19 E9
4.70 E6

3.98 E4
5.30 E4
4.80 E4
3.50 E4








Table 4. continued.

Raw Trans-
Units formity Emergy
Note" Name (units/yr) (sej/unit) E18 sej/yr

15 ELECTRICITY (1983) 4.58 E14 J 1.59 E5 72.8
16 GOODS & SERVICES (1983)
Direct 2.10 E8 $ 3.00 E12 630.0
Imports 4.80 E7 $ 3.80 E12 182.4
Taxes 2.96 E16 3.00 E12 8.9
17 TOTAL INPUT 7539.5

sej = Solar equivalent joules
'Refer to numbered notes and calculations given in the appendix.

Table 5. Emergy flows of primary productivity (1960s).

Raw Trans-
Units formity Emergy
Note* Name (units/yr) (sej/unit) E18 sej/yr

3 TIDE 6.90 E16 J 2.36 E4 1625.9
2 Chemical Potential 4.90 E16 J 1.54 E4 756.5
2 Kinetic Energy 2.88 E14 J 8.89 E3 2.6
12 Phosphate 5.95 E8 gm 1.40 E10 8.3
12 Nitrate 2.08 E9 gm 4.19 E9 8.7

6 Geopotential 2.29 E15 J 2.36 E4 54.0
10 Phosphate 3.77 E10 gm 1.40 E10 630.0
10 Nitrate 2.11 Ell gm 4.19 E9 1227.7

7 Chemical Potential 1.91 E16 J 4.11 E4 784.4
11 Phosphate 5.07 E8 J 1.40 E10 7.1
11 Nitrate 7.14 E9 J 4.19 E9 29.9

7 Chemical Potential 5.50 E14 J 4.11 E4 22.6
11 Phosphate 1.50 E7 gm 1.40 E10 0.2
11 Nitrate 2.19 E8 gm 4.19 E9 0.9

9 PRIMARY PRODUCTION 4.75 E17 J 1.09 E4 5158.8

sej = Solar equivalent joules
aRefer to numbered notes and calculations given in the appendix.

1920's 1960's 1980's



Figure 9. Average annual EMERGY inflowing to the Sea of Cortez for temporal periods 1920s,
1960s, and 1980s. Data are from Tables 2-5.



1920's 1960's 1980's



Average annual EMERGY inflowing to primary production in the Sea of Cortez for the
temporal periods 1920s, 1960s, and 1980s. Data are from Tables 2-5.

Figure 10.

1950 1955 1960 1965 1970 1975 1980



r /
I | 1I / / / I
7~ ew111111 I
Ile, //
I* ell' /
r /o<,/*/
eo/ / /

C~-p CM N/ q3 9 ;2

1950 1955

1960 1965 1970 1975


The number of new fishing boats commissioned each year that are still fishing (top) and
cumulative number of boats (bottom). Data are from records of Delegacion Federal de
Pesca en Sonora.

X1I 1






P n /
/ / /









Figure 11.

Figure 12. Summary diagram of the Sea of Cortez shrimp fishery showing driving energies inflowing
from left and bought goods and services and the economic sector to the right. N =
nutirents, Sed. = sediments, B = benthic organisms

Emergy costs and shrimp yield per year: Shrimp Trawlers.

formity* Emergy
Footnote" Name Actual Units (sej/unit) E15 sej/yr

1 Fuel 7.2 E12 J 53000 sej/J 380

2 Misc. Goods & Svcs $6.6 E4 2.9 E12 sej/$ 200

3 Salary $1.7 E4 2.9 E12 sej/$ 50

4 Boat $4.1 E3 2.9 E12 sej/$ 10

5 Engine $4.1 E3 2.9 E12 sej/$ 10


6 Shrimp 3.8 E10 J 8 E6 sej/J 300

Catch/effort ratio:

300 E15 sei/vr
650 E15 sej/yr

= 0.46/1 (Net Emergy yield ratio)

*Transformities for fuel, dollars, and shrimp are from Odum et al. (1986). The transformity for dollars is the
total Solar Emergy driving the Mexican economy divided by the GNP in U.S. dollars.

"Refer to numbered notes and calculations given in the appendix.

Table 6.

Emergy costs and shrimp yield per year: Small boats (Pangas).

Trans- E15 sej/yr
Footnote' Name Actual Units formity* (sej/unit)

1 Fuel 1.35 Ell J 53000 sej/J 7.2

2 Misc. Goods & Svcs $ 879 2.9 E12 sej/$ 2.6

3 Salary $2400 2.9 E12 sej/$ 6.7

4 Boat $ 50 2.9 E12 sej/$ 0.1

5 Engine $ 271 2.9 E12 sej/$ 0.8


6 Shrimp 1.1 E10 J 8 E6 sej/J 88.0

Catch/effort ratio:

88.0 E15 sej/yr
7.4 E5 sej/yr = 5.1/1 (Net Emergy yield ratio)
17.4 E15 sej/yr

*Transformities for fuel, dollars, and shrimp are from Odum et al. (1986). The transformity for dollars is the
total Solar Emergy driving the Mexican economy divided by the GNP in U.S. dollars.

"Refer to numbered notes and calculations given in the appendix.

Table 7.

Figure 13. Summary diagrams of EMERGY and dollar flows for the large boat shrimp fishery (top) and
pangas shrimp fishery (bottom) in the Sea of Cortez. Data are from Tables 6 and 7. P =
production, C = consumer organisms



In this section we develop a synthesis overview of the Sea of Cortez, its driving energies, its storage and
processes, and its place in the Mexican economy. We examine public policy implications of present and past
resource management and suggest alternatives that may maximize long-term economic vitality. Of greatest
concern is the issue of sustainable economic development. Throughout the development world, the single most
important issue facing public officials is related to the long-term consequences of selling raw resources abroad
and thus in essence supporting the economy of other nations at the expense of the local economy. The methods
and results of emergy analysis highlight this issue and may make policy decisions more easily understood.
Consider first the way the Colorado River and tidal inputs to the Sea of Cortez support primary production
and food chains leading to fisheries that have immense value to the economy.

The Effect of the Colorado River Diversion

The discharge rates of the Colorado River during the 1920s were taken as a baseline for the era preceding
heavy influences by humanity. Since 1935, discharge of the Colorado has been significantly altered (Figure 2).
Both low flows and annual peak discharges have been reduced. The average flows during the 1980s represent
current flow rates and are about 33 % of those recorded during the 1920s.
The effects of diversion and decreased discharges of the Colorado River on the Sea of Cortez have been a
source of speculation for a number of years. With such a large discharge, it has been speculated that the
diversion and losses of river water as agriculture and damming increased should have had a deleterious impact
on the Gulf. Indeed, when comparisons among Tables 2, 3, and 4 are made, the magnitude of river diversion
is significant. The contribution of river-derived phosphorus, nitrogen and organic matter, as well as chemical
potential of freshwater, were a significant portion of the northern Gulf's yearly net emergy inflow (40%) during
the 1920s. The energies given in the last column of the tables are calculated by determining net inflows from
all outside driving energies. The loss of discharge during the 1960s resulted in a loss of almost 40% of the net
yearly emergy flux, and present day discharges still contribute only about 70% of the original net emergy to the

The single greatest emergy input to the northern Gulf during the 1920s (Table 2) is the emergy of the
chemical potential of the freshwater input from the Colorado discharge. Indeed, Alvarez-Borrego (1983) felt
that "the greatest changes in the upper Gulf...[are due to] the decrease of Colorado River fresh-water input
[that] has drastically changed the ecological conditions of what used to be an estuarine system, and is now an
area of the highest salinities of the whole Gulf." Copeland (1966) suggests that the most important
hydrobiological parameter in estuaries is salinity, and if river flow is diminished by activities in the upper
watershed, salinity in the receiving estuary may increase to levels that are detrimental to biological communities.
However, he also questions whether the loss of freshwater input actually results in lessened productivity in the
estuary or only in changes in the channels of productivity.
Budgets of Water, Organic Matter, and Nutrients
While the energy analysis suggests that significant changes in the total emergy of the upper Gulf resulted
from the diversion of the Colorado River, comparison of the year fluxes and storage of water, organic matter,
PO -phosphorus and N -nitrogen lend additional insight. The magnitudes of inputs resulting from the Colorado
and those from net tidal flux and overall storage within the upper Gulf are shown in Figures 7 and 8. In
general, they suggest that internal cycling and tidal flux may account for more importance than the inflows
resulting from the Colorado.
Fresh Water. Figure 7a gives the water balance in the upper Gulf during the 1920s. Comparison of
the magnitudes of inflowing water from the river and net tidal inflow indicates how small the river
input actually is. Calculated evaporation is more than 10 times the inflow of the river. Yearly
rainfall over the Gulf is half of the inflow from the Colorado. Just in terms of volume of the
exchange of the tidal prism, the yearly exchange of water is three orders of magnitude greater than
the yearly input from the river. Yet the influence of the Colorado's fresh water, when considered
relative to its energy input as chemical potential energy (Table 2) was the greatest single input
during the 1920s era.
Organic Matter. The yearly fluxes and storage of organic matter in the northern Gulf as shown in
Figure 7b indicate that the Colorado River's contribution is nearly 3% of the total storage. Tidal
flux of organic matter is difficult, at best, to calculate, since it depends in part on the effects of
mixing resulting from currents around the mid-riff. So comparisons between river input and net
tidal flux may be inappropriate. Yet if the net tidal flux shown in Figure 7b is an indication of the
relative magnitudes, river inputs of organic matter were six times greater than the net tidal flux.
Comparison between river inflow and total tidal exchange, on the other hand suggests that the river
represents approximately 3 % of the overall balance of inflows and outflows. In terms of the total
flux of organic matter, the Colorado contribution seems small, but may have been extremely
important in the yearly budget of organic matter.

Nutrients: The determination of net tidal flux of nutrients between the upper and lower Gulf
depends on how well mixed the zone between these two water masses is, since the exchange occurs
over this relatively small interface. The currents in the mid-riff area of the Gulf are exceptionally
complex, thus determination of actual exchange of nutrients is further compounded in complexity.
Nevertheless, if a simplifying assumption (complete mixing at the interface) is made, relative
comparisons between magnitudes of river inputs of phosphorus and nitrogen and those resulting from
tidal exchange can be made. Figures 8a and 8b suggest that river inputs of P04-P and NO3-N are
quite small when compared to internal cycling. The effects of river diversion on nutrient budgets of
the upper Gulf would seem to be of lesser importance than those of organic matter and the chemical
potential energy of its fresh water, since the volume of these materials and internal cycling seem to
be at least three orders of magnitude greater than river inputs.
Summary: Impacts of the Colorado Diversion
It is somewhat surprising that apparently there was not a decline in the fishery recorded in the northern
Gulf after the diversion in the 1960s as a result of the loss of emergy of this magnitude. The reason for a lack
of measurable decline in productivity over large areas of the Gulf (Zeitzschel 1969 concluded, after
measurements in 1968, that productivity in the northern Gulf was approximately 0.6 g C/m2 day) may be related
to the nature of the emergy inputs. The major components of the emergy inflowing to the Gulf as a result of
the Colorado River discharge were the chemical potential energy of freshwater and organic silts, both of which
would have their strongest impact at the delta and immediate surrounding areas. The loss of emergy of
estuarine upwelling that was generated by the chemical potential (of the order of ten times the river water input
[Gross, 1982]) would probably have a direct impact on the primary production in areas relatively close to the
river discharge. Direct impacts on the benefits and protection derived by benthic filter feeders and a few
notable species of fish such as totoaba (Cynoscion macdonaldi [Flanagan and Hendrickson, 1976]), from the
organic silts and salinity fluctuations would be local as well.
Aside from these local effects, the lack of a more pervasive impact on the productivity of the northern Sea
of Cortez may be related to the buffering capacity of the large storage of nutrients and organic matter within
deep waters and sediments of the Gulf and their availability via upwelling and tidal resuspension. When the
river inflows during the 1920s are compared to the storage of each material within the northern Gulf and the
yearly flux of each as a result of tidal exchange and ocean currents, the amounts of river-derived organic matter
and nutrients are minor (Figures 7 and 8). Yearly fluxes shown in Figures 7 and 8 are for the "unaltered
condition," prior to intervention by humanity, that is represented by the 1920s data. During this time, discharge
of the river represented only about 0.01% of the total volume of water in the northern Gulf, and yearly organic
matter contribution was about 0.4% of the total volume of organic matter. The contributions of phosphorus and
nitrogen in river water were small when compared to their volumes (about 0.01% and 0.02%, respectively).

Thus, when the river was diverted during the 1960s, the loss of these constituents was buffered by the enormous
storage within the northern Gulf and exchanges with the Pacific.

Primary Production

A major part of the ecosystem is primary production of the phytoplankton which supports food chains.
Figure 6 shows the way the rest of the system interacts. A separate analysis was performed for the euphotic
zone subsystem. Given in Table 5 is an emergy analysis of primary production for the Sea of Cortez during the
1960s. Data on primary production were available for the 1960s (Zeitzschel, 1969), thus the 1960s emergy data
(Table 5) were used to calculate emergy input to primary production. The area for which primary production
calculations were made is comprised of the surface of the northern Gulf to a depth of roughly 40 meters (the
photic zone). Therefore, not all the emergy inputs to the northern Gulf are used in the calculations of emergy
for primary production. Those like sunlight, wind, and hurricanes that are already embodied in rainfall are not
double counted. Organic matter that must sink below the photic zone and decompose before upwelling as
nutrients is not included since the upwelled nutrients are included, and seismic activity, which is much below
the photic zone, is not included.
The emergy column in Table 5 expresses the various energy inputs to primary production in the northern
Gulf in common units of Solar Emergy. The single largest input is the physical energy in tides, followed in
order of importance by nitrate in sea water, chemical energy in runoff from the surrounding lands, and the
chemical potential energy in rainfall. During the 1960s, the relative contributions from the Colorado are quite
small. Figure 9 illustrates the relative importance of the inputs derived from the Colorado. Emergy inflows
derived from the Colorado during the 1920s were nearly half of the total emergy budget, were nearly absent
during the 1960s, and represent about 20% of the total emergy budget during the 1980s.
Theory suggests that with the loss of emergy contribution from he river discharge after the 1920s, there
could have been a corresponding decline in primary production. The change in primary production over time
and how it has been affected by the decline in river flow and consequent decline in emergy input is still open to
speculation, since there are no data during the earlier years when the Colorado discharges were greater.
However, if we assume that there is a direct relationship between the total emergy input and primary production
in the northern Gulf, then the annual emergy inputs for the three time periods that are illustrated in Figure 9
might be used to suggest changing primary production from the 1920s through the 1980s. From emergy
contributions in Figure 9, we might speculate that current primary production in the northern Gulf is about 75%
of that which was characteristic of the area when the Colorado River discharged unimpeded by the works and
uses of humanity.

Fisheries in the Sea of Cortez

The shrimp fishery of the northern Sea of Cortez is the single largest fishery of the entire Mexican
economy, contributing more than $350 million. In the same year, the total commercial fishery catch for all
species from the Sea of Cortez contributed over 55% of the total value of the Mexican commercial fishery.
In recent years the Mexican government has been monitoring the shrimp fishery and, as a result, much
data on total catch have been collected. However, it still remains to be seen if these data can be used to relate
catch to population size and then to outside influences like changes in the discharge rates of the Colorado. The
response of the fishery to changes in the Colorado may be overridden by changes in the intensity of fishing by
the Mexican fleet (Flanagan and Hendrickson, 1976).
To better understand these trends in the shrimp fishery of the northern Gulf, we examine the emergy
analysis of the costs and yield of shrimp trawlers (i.e., more energy intensive equipment) and the costs and
yields of small boats. Figure 12 is a summary diagram of the shrimp fishery showing the driving energies,
gross production, the simplified estuarine food chain, and harvesting efforts using boats and equipment
purchased from outside. Tables 6 and 7 summarize the emergy analysis for large and small boats. The shrimp
trawler is typically of a size class of about 100 tonnes, driven by a 400 hp diesel engine. The small boat is a
fiberglass boat called a "panga" typically about 5 meters in length with a 42 hp outboard motor. Currently the
shrimping fleet of the northern Gulf is comprised of about 587 shrimp trawlers and about 1600 to 1800 pangas.
An important index calculated in the emergy analysis is the ratio of catch to effort. By comparing the
emergy of the shrimp caught per year with the sum of the total emergy costs of operation, maintenance, labor,
and boat replacement for each of the two types of boats, a catch to effort ratio is calculated and shown at the
bottom of Tables 6 and 7. The ratio relates the total emergy of the shrimp catch with the total emergy cost of
the effort. For the shrimp trawlers, the ratio is 0.46/1, indicating that for one joule of emergy in shrimp caught
roughly 2 joules are utilized in fishing effort. The ratio for the pangas fishermen is about 5/1, indicating that
for each joule of emergy used in fishing effort, 5 joules of shrimp emergy are caught. While there may be
some question concerning the reliability of the data for the pangas fishing system because the data are based on
dockside interviews of fishermen, the analysis suggests, unless our estimates from interviews are off by two
orders of magnitude, that the smaller boats are more efficient.
From a larger scale perspective, if the differences between these two methods of fishing are as dramatic as
indicated by these data, policy that encourages larger boats may in the long run be counterproductive, as the
large boats require nearly 12 times the energy to harvest the same shrimp as the smaller boats. Other factors
affect these decisions, however. First, the larger boats can fish for shrimp in areas where it would be difficult
or impossible with the smaller boats that are confined to the relatively calm coastal waters. Second, the large

boats can fish a more dilute fishery; the smaller boats require a more concentrated fishery, since their methods
are not those of dragging nets for hours at a time in deep waters. Third, the larger boats are better able to
preserve their catch, thus ensuring a high quality product for the export market.
Policy also needs to consider the effects of the shrimp fishery on the economy. As we have shown, the
shrimp fishery of the northern Gulf is important to the economy of Mexico, contributing over a 55% share of
the total income derived from fishing nationally. Figure 13 summarizes the two methods of shrimp fishing and
relates each to the economy. The top diagram summarizes the flows of emergy and money for the shrimp
trawlers, and the bottom diagram summarizes the flows for the pangas. The striking difference between the two
diagrams is the relative proportions of the dollar budgets that are spent on fuels, goods and services compared
to labor. Almost 70% of the total income derived from the export of 100% of the catch from the shrimp
trawlers (top diagram) is used to purchase fuels, goods, and services, while about 33 % of the pangas' income is
used to purchase those inputs. The remaining income for each type of boat is spent in salary and considered as
direct inputs to the local economy. In other words about 66 % of the pangas' income is spent as salary, while
only 30% of the shrimp trawler income is salary, an interesting consequence since recent government policy has
been to encourage the larger boats because of the number of individuals they employ.
A second difference is related to income generated from the sale of shrimp. The emergy per dollar of
catch from shrimp trawlers is about 3.3 E12 sej/$, while the emergy per dollar of the catch from the pangas is
about 24.4 E12 sej/$. This is a reflection of the difference in price obtained by the pangas fisherman as a result
of lower quality catch and local market conditions. Interestingly, though, the local economy benefits more from
the sale than does the external buyer.
When goods are purchased from the U.S. economy with the income earned from the sale of shrimp, the
net trade balance favors the U.S. economy since the emergy per dollar ratio for the U.S. economy is 2.4 E12
sej/$, while that for shrimp caught by shrimp trawler is 3.3 E12 sej/$.
Other aspects of the shrimp fishery that may have implications and affect policy decisions are related to
the environmental impacts of the two methods of fishing. It was estimated by Delegacion Federal de Pesca En
Sonora personnel that the by-catch (the other fish caught in nets during shrimping) is at times twice the weight
of shrimp caught. Our observations were that as much as 90% of a haul was by-catch at the end of the 1986
fishing season. Most of the by-catch dies on the decks of the shrimp boats before being returned to the Gulf
waters. If the average weight of the 50% by-catch is that of the shrimp caught over the entire shrimping
season, adding the by-catch to the emergy costs in Table 6, decreases the catch to effort ratio from 0.46/1 to
0.32/1. The by-catch of the pangas fishermen is minor, and any commercial fish in the by-catch may get into
the local economy at day's end. In essence, the smaller boats have a smaller environmental impact. Pauly and
Neal (1985) have found the same is true in Southeast Asian fisheries.
Mathews (1974) estimated that every square meter of the shrimp grounds in the Gulf are passed over 7
times each year by the nets of the shrimping fleet. In August 1986, we used data gathered from the Delegacion

Federal de Pesca En Sonora and determined that the total area dragged for the entire fleet was 1.2 Ell m2 for
the previous fishing season. And, if we assume that 1/4 the area of the northern Gulf (1.97 E10 m2) is dragged
for shrimp, this would mean that, on the average, each square meter would be dragged 6.1 times. In reality,
the area of shrimp harvesting is probably smaller than 1/4 of the northern Gulf, and some areas are dragged
more frequently than others, so that the number of times the shrimp nets pass over these areas may be much
The summary diagram of large boat shrimp fishing in the northern Gulf, given in Figure 14, shows the
relationship of emergy flows driving productivity (flow from the left) of the fishing area for an average large
boat, and the emergy associated with fishing effort (flow from the right). Combining these two flows of
emergy as a ratio, where the renewable emergy from nature is the denominator and the emergy in human effort
is the numerator, yields the investment ratio, which relates the emergy "invested" to the renewable emergy
driving a system. Put another way, it is a measure of environmental loading, the "load" of input stresses that
the environment must handle during the course of a particular human activity. A high ratio suggests high
environmental loading, while a low ratio suggests low environmental loading. The investment ratio for shrimp
fishing using large boats is about 0.25/1. Investment ratios for other food systems are also given in Figure 14
for comparison.
The investment ratio for shrimp fishing when compared to other food systems suggests that the
environmental loading is significantly less than that of other food technologies. Data on the area of shrimping
grounds for the smaller boats were not available and comparisons between these technologies were therefore not
possible (although using an estimate of area per small boat of 1/100th that of the large boat would yield an
investment ratio of almost 0.07/1).
When viewed in the context of the maximum emergy principle, these data suggest efficiency is not the
primary principle by which selective processes operate to allocate resources, but rather they operate so as to
maximize the rate of resource use. In so doing, the larger system (in this case, the economy) maximizes
emergy flow. Clearly, the data suggest that the panga is the more efficient fishing boat, but much less
"productive" than the shrimp trawler, since a trawler can catch a larger amount of shrimp in a shorter period of
time. All other things being equal, and as long as the costs of energy and machinery remain low, trawlers
make "good economic sense." On the other hand, good economic sense does not address sustainability or the
future availability of energy and machinery. Overfishing, in the long run, may undermine the capacity of the
population to regenerate. Without a productive, balanced population, the fishery cannot sustain high catch rates
nor support the high economic investments in trawlers that are currently being made. Current costs of energy
and machinery and the present abundance of shrimp in the northern Gulf favor energy intensive processes for

~- -~--


Shrimp Investment Ratio +

Other Investment Ratios

Brazilian Cacao
USA Ind. Corn
Texas Agriculture
New Zealand Sheep
Rainforest Pulp Plantation
Rainforest Wood Power Plant
Subsistance Corn




Figure 14. Diagram summarizing the investment ratio for the large boat shrimp fishery in the Sea of Cortez.
Data are from Table 7. Investment ratios for other resource extraction and food systems are given
for comparison.


Shrimp Fishery
(1 boat)

E17 sej/yr.

= 0.25/1

Yet, if either of these two factors change (i.e., if energy costs rise or populations decline), the ability of
the fishery to sustain high economic investment is diminished. Conditions may then favor the smaller, more
efficient pangas; however, in spite of the higher total investment costs for shrimp trawlers, as compared to
pangas, the investment ratio (0.25/1) is low compared to other land based food systems (Figure 14). This
should not be surprising since land based agriculture requires purchased energy input for cultivation, protection,
and harvest while fishing relies on free services and emergy for most population support functions and only
requires purchased energy for harvest.

The Sea of Cortez and the Economy of Mexico

The total emergy flow of the present Sea of Cortez from Table 4 is about 7540 E18 sej/year, which is 2%
of the Mexican National emergy from Table 1. The total emergy driving primary production in the northern
Sea of Cortez during the 1980s is about 6.4 E21 sej, while the total emergy budget for the Mexican economy as
a whole was about 34.6 E22 sej (Table 1). Thus primary production in the northern Sea of Cortez represents
approximately 1.5% of the national economy. The importance of the Colorado discharge in terms of its values
to the overall economy, then, represents about 0.4% of the national economy (20% of 2%). The gross effect of
the loss of Colorado River water between the 1920s and 1980s (where the contribution of the discharge in the
1920s would have been approximately 0.8% of today's economy) is a loss of 0.4% of the emergy driving the
economy, or a reduction in economic activity of 0.4%. The magnitude of loss when related to the national
economy suggests, its importance can (and did) go unnoticed in light of other more significant factors perceived
to affect the national economy in a more direct manner.
The importance of primary production in the northern Gulf to the economy of coastal regions of Sonora
and the Baja Peninsula is more significant. Comparison among the emergy inflows to the region given in Table
4 shows that of the total emergy inflowing more than 80% is from sources directly related to the northern Gulf.
In other words, the energies associated with the northern Gulf account for more than 80% of the local
economy, and, as a result, they are by far the most important constituent of the local economy. While seemingly
unimportant to the national economy of Mexico, primary production in the northern Sea of Cortez represents
80% of the resource base of the coastal region of Sonora and the Baja peninsula. Policy decisions and
management alternatives that affect the northern Gulf should be concerned with and reflect regional implications
first and national concerns only secondarily.
To effectively manage the Sea of Cortez fishery, the trends of primary production are especially
important. With increasing pressure to use the Colorado for irrigation, thus lowering discharges and increasing


salinities in the Northern Gulf, the impacts on the fishery and consequently on the economy of the Gulf States
and, for that matter, the whole of Mexico, are unknown, yet they may be significant.

Local Use of Fisheries Versus Export Sales

The shrimp fishery of the northern Sea of Cortez has been increasingly exploited by a larger and more
energy intensive fishing fleet within the last decade, anrd the local and national economy have been increasingly
affected. In the old pattern of resource use, small boats with small nets harvested shrimp for local
consumption, while in the modern pattern, large boats and large nets harvest the resource primarily for export.
Recently there have been expressions of concern that the growing shrimping fleet of the northern Gulf (see
Figure 11) may be overexploiting the resource. Combined with unknown impacts of decreased Colorado River
flow, the increasing fleet size may increase the likelihood of a collapse of the fishery.
Generally, as a resource, like the shrimp population in the northern Gulf, is increasingly exploited, local
markets are not large enough or developed enough to accommodate the increasing supplies, and thus the price
falls. If sales were limited to the local markets, the size of the fleet would rapidly adjust and exploitation would
track the ability of the local market to demand (or consume) the resource. However, where large outside
markets can be found, demand, can remain high, external prices will be higher than local markets can sustain,
and as production is increased to meet the demand a cycle of increasing dependence on external markets is
Once the external dependence cycle begins, it is difficult if not impossible to break because the local
demand of the resource is kept low by the high price buoyed up by the outside markets. The costs associated
with exploiting the resource increase as the technology increases and eventually, one can no longer "afford" to
sell the resource locally since the local economy cannot support the price that must be demanded.
On the other hand, the local economy is expanded as local people are involved in exploiting, processing,
and transporting the product, leading most policy makers to believe that the net effect is positive even though
external markets become increasingly influential. The money derived from exports of the resource is used to
purchase external goods, services and energy that in turn increase the ability to exploit the resource even
further. In the rush to increase the economic cycles of exports and imports, often the local economy suffers as
the emergy of the harvested resource contributes less to the home economy than to the economy that imports it.
The increasing externalization of economies throughout the developing world can lead to serious instability
in local production and economies, as well as short-run problems for national economies. Throughout Central
and South America there is a trend of changing local agricultural production from crops with food value grown
for local consumption to "specialty" crops grown exclusively for export to the United States and Europe. The


best agricultural lands are given over to these crops, sometimes greatly encouraged by well-intentioned
governments, and marginal lands are used for local food production. Monies earned from the sale of exported
crops are used to purchase consumer goods and food that are usually not locally produced. Increasingly,
fisheries are developed with external investments for the sole purpose of exporting them to help with
international balance of payments. The net effect is to drive the price so high that the local population can no
longer afford to eat the fish themselves. In many cases, they turn to lower quality sources of protein, or do
without altogether.
It is difficult to fully measure the consequences of these trends; however, in recent analysis (Odum, 1984;
Odum et al., 1986; Odum et al., 1987) we have suggested that the trading partner receiving raw materials
benefits far more than the partner who receives highly refined or manufactured goods. The emergy per dollar
spent is much higher for raw materials and resources than for finished goods. Given in Figure 15 is a summary
of the benefits to the Mexican economy versus the United States economy that are derived from the sale of
shrimp. The top diagram illustrates shrimp caught by small boats and sold in the local economy, while the
bottom diagram shows the benefits from shrimp caught using the larger shrimp trawlers and exported to the
United States. In both diagrams the amount of money that circulates is $1 and the emergy is taken from Figure
13. The net benefit to the Mexican economy is derived by dividing the emergy received (the flow to the right)
in the economy by the emergy invested (the flow to the left).
The greatest net benefit is derived from the sale of shrimp caught by traditional pangas and sold within the
Mexican economy. In this case the net benefit to the Mexican economy is about 8.6 to 1. In contrast to this
relatively large net benefit, the benefit to the Mexican economy through export of shrimp caught using shrimp
trawlers is negative (in other words, more emergy is exported to the United States than is received). This is
illustrated in the lower diagram where the trading advantage favors the United States and net benefit to the
United States is 1.4 to 1. These net benefits are based on fishing boats and trawlers that are of Mexican origin,
so that the benefits derived from sales of shrimp accrued to the Mexican economy. If the fishing trawlers are
foreign owned and only pay taxes on tonnage of shrimp or fish caught, the net benefit to the economy is much
less. While we did not evaluate this condition, it is relatively easy to visualize that the only benefit to the
Mexican economy comes from what emergy might be purchased with the taxes received.


to Mexican Economy

Figure 15. Net benefits resulting from the sale of shrimp, within the Mexican economy (top diagram) and
exported sale to the U.S. economy (bottom diagram). The upper diagram (a) illustrates the pangas
shrimp fishery and sale within the local economy where feedback is calculated using the Mexican
EMERGY/dollar ratio (from Table 1). Export sales of shrimp caught using Mexican shrimp
trawlers is illustrated in the lower diagram (b) where feedback is calculated using the
EMERGY/dollar ratio of the U.S. economy. Shrimp exported represent a net EMERGY loss to
the Mexican economy.


Analysis of the resource base of the economy of Mexico (Table 1) suggests that its largest, single, driving
energy is fossil fuels, contributing more than 80% of the total energy driving the economy. Comparison with
the evaluation of the resource base of the Sea of Cortez reveals its importance to the economy of Mexico. The
driving energies of the Sea of Cortez represent almost 3 % of the total resource base of the economy and more
than 14% of the natural resource base. Its importance is reflected in the fact that the upper Sea of Cortez is
Mexico's most productive fishery.
During the 1920s the Colorado River discharge alone represented over 8 % of the natural resource base of
the Mexican economy. Today, since its emergy has been reduced by almost 66%, its contribution to the natural
resource base of the economy has diminished to less than 4%. Concern at the national level is certainly
warranted in light of the overall contribution the Colorado River makes to the Mexican economy.
Energy analysis overview of the Sea of Cortez suggests that the northern Gulf, while having great
buffering capacity against the loss of the Colorado River discharge (because of its large volume and because of
the large volume of water exchanged with the lower Gulf and the Pacific), has still lost about 30% of the total
emergy driving the system when compared to the total emergy that may have been characteristic during earlier
periods of high discharge. The decreased emergy flow is caused more by the loss of chemical potential energy
of the freshwater in Colorado River discharge than by the losses of organic matter or nutrients. The single
largest emergy inflow to the northern Gulf during the 1920s era of high river discharge was its chemical
potential energy. Today, while the chemical potential energy of the river is high, it is exceeded by tidal energy.
Much research is needed to better understand the relationship of the Colorado discharge and continued
primary production and fishery production within the northern Gulf. While past measurements have shown very
high productivity, little is understood of this relationship. The maintenance of a viable fishery may well depend
on how well these relationships are understood so that catches might be limited during times of low flow to
ensure that overfishing is minimized.
To determine public policy relative to the Colorado River, detailed emergy analysis of the alternative uses
of freshwater for irrigation and for urban uses needs to be related to northern Gulf productivity. Optimum
configurations of agricultural, urban, and estuarine uses might be defined to ensure long-term maximum benefits
to the economy as a whole. Without question, a better understanding of the relationship of the Colorado River
to northern Gulf productivity and the value of river water to such competing uses as agricultural irrigation and
urban uses should guide policy in determining its optimum use.

Current governmental policy favors a large mechanized shrimp fishing fleet, which may be the proper
posture in light of the relatively low investment ratio compared to other food technologies. Recently there has
been much concern over other nations using highly mechanized fishing techniques and competing with the local
Mexican fleet. When a fishery is underused, as it might be if only small boats worked the shallow coastal
areas, the resource draws investment from outside sources. The best way to protect the fishery is to
competitively exclude foreign competition by "intensifying" one's own methods of fishing. Of course, this must
be managed so that the more intensive rate of exploitation is sustainable. This rate can only be determined by
thorough research on the target species and its supporting ecosystem. In the case of the Sea of Cortez,
overdevelopment may drive shrimp populations too low, and combined with an unknown relationship to the
discharge of the Colorado River, overexploitation could result. Much caution is warranted.
As we have seen in the economies of other developing nations, as they exploit their resources, their
economies become more and more externalized, relying to a larger extent on outside sources of goods and
services. This is another way of saying that the world economy is becoming more and more integrated.
However, in the rush to develop these resources, their emergy is sold for a nominal price and goods and
services bought with the proceeds have a relatively high price. The raw resources that are sold contribute much
more to the economy that purchases them than the "home" economy receives with the purchase of finished and
highly refined goods. Once the system for exploitation is in place, the overall issue that must be considered is
acknowledging the high emergy value of one's resources so as to develop a sustainable balance between export
and supporting the growth or sustainability of economies. We believe that the emergy analysis approach
presented here may help in achieving such a balance.




1. Rainfall: (0.81 m/y)(1.97 E12 m2)(1 E6 g/m3)(5 J/g) = 7.97 E18 J/yr.

2. Tides (Miller, 1980).

3. Waves (Miller, 1980).

4. Oil use, production minus exports:
[(2.7 1.5) E6 bbl/day](365 d/yr)(6.28 E9 J/bbl) = 2.75 E18 J/yr.

5. Natural gas use: production minus export.

6. Imports for 1981 (Brown, 1985). Expressed in U.S. dollars.

7. Exports for 1981 (Brown, 1985). Expressed in U.S. dollars.

8. Export of oil and gas from Mexico (273 E6 cu ft/day)(1.1E6 J/cu ft)(4.8 E4 sej/J)(365 d/y) = 0.53 E22
(250 E6 bbl/y)(6.3 E9 J/bbl)(5.3 E4 sej/J) = 8.3 E22
Total oil and gas export: 8.8 E22 sej/y

9. Electric power, coal equivalents: (239 E12 Btu/yr)(1013 J/Btu) = 2.4 E17 J/yr.

10. Total of independent import items 1,2,4,5, and 6.

11. 1982 GDP, $98.6 E9 + $23.1 E9 imports = 121.7 E9 $/yr.


1. Sunlight. Average sunlight over Gulf taken as 170 Kcal/m2 yr (Woldt and Jusatz, 1965). Area = 78700 km2
(Roden 1958).

Sun energy = 170 Kcal/m2 yr 4.187 E3 J/Kcal 10 E9 cm2/km2
78700 km2 = 560.14 E18 J/yr.

2. Rainfall. Average rainfall over northern Gulf taken as 126 mm/yr (Roden, 1958).

Velocity = 762 cm/sec (Odum et al. 1983).
Chemical potential energy: 126 mm/yr .1 cm/mm .5 1 gm/cm3
(762 cm/sec)2 2.38 E-11 Cal/erg = 87.062 E-6 Kcal/cm2
4.1867 E3 J/kCal 78700 km2 1 E9 cm2/km2 = 786.86 E12 J/yr.

3. Tide. Average tidal height taken as 109 cm over 200 m depth limit (Alvarez-Borrago, 1983).
Assumed 3/8 of energy absorbed over area of 200 m depth (43700 km2).

Tidal energy: 3/8 43700 km2 .5 x 706 tides/yr (109 cm)2
(0.01 m/cm)2 1.0253 E3 kg/m3 9.8 m/sec2
(1000 m/km)2 = 6.9 E16 J/yr.

4. Wind. Eddy diffusion coefficient = 8.4 m2/sec.

Vertical wind velocity gradient: 4.29 E-3 (m/sec)/m (Odum et al., 1983).
Wind energy = 1000 m 1.23 kg/m3 8.4 m2/sec 3.154 E7 sec/yr
[4.29 E-3 (m/sec)/m]2 78700 km2
(1000 m/km)2 = 4.72 E17 J/yr.

5. Hurricanes. Average energy per storm 5 E5 Kcal/m2 day (Odum et al., 1983); 3% kinetic energy; 10%
dispersed to surface (Odum et al. 1986); residence time/day, 1 in 10 yrs reached 20 N Lat. (Roden 1964); average
area of a hurricane = 20,000 km2 (Odum et al., 1983). Assumed area affected in Sea of Cortez is that of one
hurricane diameter.

Hurricane energy = .1/yr 1 yr/365 days 5 E5 Kcal/m2 day .003
20,000 km2 1 E6 m2/km2 4186.7 J/Kcal = 3.44 E14 J/yr.

6. Ocean Current. Net current inflow assumed equal to difference between inflows and volume of water evaporated
(2500 mm/yr) (Alvarez-Borrego, 1983).

Footnotes to Tables 2 through 5 (continued).

Colorado River inflow:
(1920s) 18.379 E9 m3/yr (USGS, 1954);
(1965-1970) 0.115 E9 m3/yr (USGS, 1976);
(1980-1984) 6.229 E9 m3yr (McCleary, 1986).

Runoff excluding Colorado River: 3.9 E9 m3 yr (Byrne and Emery, 1960);
Rainfall: 9.92 E9 m3/yr (Roden, 1958);
Evaporation: 2500 mm/yr 7.87 E10 km2 1 E-3 m/mm
= 196.75 E9 m3/yr.

Net ocean current inflow:
(1921-1930): 196.75 E9 m3 18.38 E9 m3 3.9 E93 9.9 E9 m3 = 164 E9 m3.
(1965-1970): 196.75 E9 m3 .115 E9 m3 3.9 E9 m3 9.9 E9 m3 = 182 E9 m3.
(1980-1984): 196.75 E9 m3 6.23 E9 m3 3.9 E9 m3 9.9 E9 m3 = 176 E9 m3.

Geopotential energy integrated over one year:
(1921-1930): 164 E9 m3 2500 mm 1 E-3 rm/mm 1/2 1027 kg/m3 9.8 m/s2 = 2.07 E15 J.
(1965-1970): 182 E9 m3 2500 mm 1 E-3 m/mm 1/2 1027 kg/m3 9.8 m/s2 = 2.29 E15 J.
(1980-1984): 176 E9 m3 2500 mm 1 E-3 m/mm 1/2 1027 kg/m3 9.8 m/s2 = 2.22 E15 J.

7. River (Chemical Potential.) Salinity in 1920s taken as approximately 400 mg/L (Applegate,
1986); in 1960s approximately 1000 mg/L (USGS, 1976); in 1980s approximately 800 mg/L
(Applegate 1986).
Other runoff: 3.9 E9 m3 -- assume salinity of 400 mg/L (Byrne and Emery, 1960).

Chemical Potential:
1920s: 18.379 E9 m3/yr 8.33 J/mole 300 K 1 mole/18 gm
1 E6 gm/m3 Ln [(1 E6 400)/9.65 E5] = 89.89 E15 J/yr.
1960s: .115 E9 m3/yr 8.33 J/mole 300 K 1 mole/18 gm
1 E6 gm/m3 Ln [(1 E6 1000)/9.65 E5] = .55 E15 J/yr.
1980s: 6.229 E9 m3/yr 8.33 J/mole 300 K 1 mole/18 gm
1 E6 gm/m3 Ln [(1 E6 800)/9.65 E5] = 30.12 E15 J/yr.

Other Runoff:
3.9 E9 m3 138.83 E6 J/m3 Ln [(1 E6 400)/9.65 E6] = 19.07 E15 J/yr.

8. River (Organic Matter). Sediments are 27% silt and 5% of that is organic (Byrne and Emery, 1960).

Sediment Load (Byrne and Emery, 1960; Fortier, 1928; McCleary, 1986):
1920s: 180 E6 T/yr;
1960s: .007 E6 T/yr;
1980s: .55 E6 T/yr;

Using data from McCleary (1986) for sediment load during 1970-1979, the following relationship between
sediments and discharge was regressed.
Sediments (T/y) = 1.778 E-9 discharge (m3/yr) 14.
Sediments from other runoff sources approximately 30 E6 T/yr (Byrne and Emery 1960).

Footnotes to Tables 2 through 5 (continued).

Colorado River Organic Matter:
1920s: 180 E6 T/y .27 .05 1 E6 gm/T 5.4 Kcal/gm 4186.7 J/Kcal = 54.94 E15 J/yr.
1960s: .007 E6 T/y .27 .05 1 E6 gm/T 5.4 Kcal/gm 4186.7 J/Kcal = 2.14 E12 J/yr.
1980s: .55 E6 T/y .27 .05 1 E6 gm/T 5.4 Kcal/gm 4186.7 J/Kcal = 1.67 E14 J/yr.

Other Runoff Organic Matter:
30 E6 T/y .27 .05 1 E6 gm/T 5.4 Kcal/gm 4186.7 J/Kcal = 9.15 E15 J/yr.

9. Primary Productivity (1968).

North Gulf (average December) .572 gm C/m2 d (C14 method by Zeitzschel, 1969).
South Gulf (average December) .737 gm C/m2 d (C14 method by Zeitzchel, 1969).
South Gulf (average May) .308 gm C/m2 d (C14 method by Zeitzchel, 1969).
For southern Gulf, spring productivity is 42% of winter. If same drop is assumed for the
northern Gulf, then May productivity is approximately
.42 .572 gm C/m2 d = .24 gm C/m2 d.
Average for year = (.572 + .24)/2 gm C/m2 d = .41 gm C/m2 d.

C14 method underestimates gross production (Mann, 1982; Valiela, 1984). Estimates range from 1/5 to
1/15 actual productivity, however, we will be conservative and assume 3 times
this productivity:
3 x .41 gm C/m2*d = 1.23 gm C/m2 d.
(7.87E 10 2)(1.23 gc/m2/d)(365 d) = 3.53 E13g C/yr.

10. Nutrients Carried by Current.

Pacific equitorial current: 2.6 AM PO4 (Warsh et al., 1972).
Average Gulf concentration: 1.8 /M PO4 (see Footnotes to Figs. 7-8, No. 3).
2.6 uM 1 E3 L/m3 1 E-6 mole/umole 95 gm/mole = 0.25 gm/n3.
1920s: 0.25 gm/m3 164 E9 m/yr = 40.5 E9 gm/yr.
1960s: 0.21 gm/m3 182 E9 m3/yr = 45.0 E9 gm/yr.
1980s: 0.21 gm/m3 172 E9 m3/yr = 42.5 E9 gm/yr.

Nitrate: Regression for nitrate /M NO3 = 16.2 pM PO4 16.2 pM (Alvarez-Borrego, 1983).
Therefore, 2.6 /M PO4 predicts have 25.9 MM NO3.
Average Gulf concentration: 13 AM NO3 (see Footnotes to Figs. 7-8, No. 4).
25.9 AM 1 E3 L/m3 1 E-6 mole/mole 62 gm/mole = 1.61 gm/m3.
1920s: 1.61 gm/m3 164 E9 m'/yr = 263.4 E9 gm/yr.
1960s: 1.61 gm/m3 182 E9 m/yr = 293.0 E9 gm/yr.
1980s: 1.61 gm/m3 172 E9 m3/yr = 276.9 E9 gm/yr.

Organic Matter: Approximately 7.1 mg C/L assumed for incoming current. This number is from
Mississippi coastal waters where P04 and NO3 concentrations were comparable to those above
(Costanza 1983).
Average Gulf concentration: 1.5 mg C/L (see Footnotes to Figs. 7-8, No. 2).
7.1 gm C/m2 1.72 gm OM/gm C 6.5 Kcal/gm 4816.7 J/Kcal = 3.8 E5 J/m3.
1920s: 1.4 E5 J/m3 164 E9 m/yr = 62.7 E15 J/yr.
1960s: 1.4 E5 J/m3 182 E9 m/yr = 69.6 E15 J/yr.
1980s: 1.4 E5 J/m3 172 E9 m/yr = 65.8 E15 J/yr.

Footnotes to Tables 2 through 5 (continued).

11. Nutrients in Colorado River and Other Runoff.

Colorado River: PO4 is about .13 mg/L = .13 gm/3 (USGS, 1970).
NO3 is about 1.9 mg/L = 1.9 gm/m3 (USGS, 1970).

Other Runoff is assumed to be close to these values.

1920s: .13 gm/m3 18.38 E9 m3/yr = 2.39 E9 gm/yr.
1960s: .13 gm/m' .115 E9 m'/yr = 1.5 E7 gm/yr.
1980s: .13 gm/m3 6.23 E9 m/yr = 8.1 E8 gm/yr.

Other Runoff: .13 gm/m3 3.9 E9 m3/yr = 5.1 E8 gm/yr.

1920s: 1.9 gm/m3 18.38 E9 m3/yr = 34.9 E9 gm/yr.
1960s: 1.9 gm/m3 .115 E9 m3/yr = 2.19 E8 gm/yr.
1980s: 1.9 gm/m3 6.23 E9 m/yr = 11.84 E9 gm/yr.

Other Runoff: 1.9 gm/m3 3.9 E9 m3/yr = 7.41 E9 gm/yr.

12. Nutrients in Rain.

PO4 = .06 mg/L (Hendry and Brezonik, 1980; Graham, et al., 1979);
NOx = .21 mg/L (Hendry and Brezonik, 1980); Chapin and Uttormarsh, 1973);
Org C assumed to be 1 ppm (1 mg/L).

Phosphate: .06 gm/m3 9.92 E9 m/yr = 5.95 E8 gm/yr.

Nitrate and Nitrite: .21 gm/m3 9.92 E9 m3/yr = 2.08 E9 gm/yr.

Organic Matter: 1 gm/3 Org C 1.72 gm OM/gm C 5.4 Kcal/gm 4186.7 J/Kcal
9.92 E9 m3/yr = 3.8 E14 J/yr.

13. Seismic Activity (Earthquakes).

Effective Peak Acceleration = .5 X (force of gravity) (Odum et al., 1983).
Frequency 613.8/100 yrs (Odum et al., 1983).
Fault Length approximately 530 km (Alvarez-Borrego, 1983).
Fault Width approximately 3 m (Alexander, 1978).
Energy = k, A2 f (k, = 4168) (Odum et al., 1983).

Es = 4168 (.5)2 6.138 4186.7 J/Kcal = 2.68 J/m2 *yr.
2.68 E7 J/m2eyr 3 m 530 km 1 E3 m/km = 4.26 E13 J/yr.

14. Fuel Use in Coastal Region (based on percent of Mexico's population).

Total population (1983) 75,103,000 (UN, 1985).
Coastal population: Guamos (1969) 60,981; Puerto Penasco (1970) 10,245; estimate for the rest of the
northern gulf coastal area 29,000. Total approximately 100,000 (Webster's Geographical Dictionary,

Footnotes to Tables 2 through 5 (continued).

Population increased at a rate of 2.6% per year (UN 1985). This yields an increase of
40% from 1970 to 1983.

100,000 + (.4 100,000) = 140,000.
(140,000/75,103,000) 100% = 0.19% of total population.

Fossil Fuel Use (1983) (UN, 1985);
Coal: 3.346 E6 T coal eq/yr 3.18 E10 J/T coal eq 0.0019 = 2.02 E14 J/yr.
Oil: 88.270 E6 T coal eq/yr 3.18 E10 J/T coal eq 0.0019 = 5.33 E15 J/yr.
Gas: 32.914 E6 T coal eq/yr 3.18 E10 J/T coal eq 0.0019 = 1.99 E15 J/yr.
Wood: 2.525 E6 T coal eq/yr 3.18 E10 J/T coal eq 0.0019 = 1.53 E14 J/yr.

15. Electricity Use (based on percent of population).
66.954 E9 kWh/yr 3.6 E6 J/kWh 0.0019 = 4.58 E14 J/yr.

16. Goods and Services (assume fisheries are the major industries).

Mexico's GDP: 1.4274 Ell $US/yr (UN, 1985);
Mexico's fish production: 1.07 E6 T/yr (UN, 1985);
Emergy Dollar Ratio for Mexico: 2.86 E12 sej/$US (Odum 1984);
Transformity for fish: 8 E6 sej/J (Odum 1984);
Fish are .2 dry/wet weight and 5 Kcal/gm (dry) (Parsons et al., 1977; Kemp et al., 1975).
1.4274 Ell $US/yr 3 E12 sej/$US = 4.28 E23 sej/yr.
1.07 E12 gm/yr .2 dry/wet 5 Kcal/gm (dry) 4186.7 J/Kcal
8 E6 sej/J = 3.58 E22 sej/yr.

Fishing is (3.58 E22/4.14 E23) 100% = 8.7% of Mexico's economy.
Assume 1/4 of this is from Sea of Cortez.

17. Total Emergy Imput is sum of emergy of rain, tide, ocean currents, river inflow, other runoff: seismic activity,
fossil fuels, and goods and services. Other emergies shown in the table are not added to minimize double counting.


General Note: All data were provided by Delegacion Federal de Pesca En Sonora, Departamento de Flota E Industria,
Guaymas Sonora, Mexico. From data collected during the month of July, 1986, and for the 1984-1985 shrimping year.

1. Fuel use = 1,200 I/day. Total days calculated as 160 days/yr by dividing total working days (55006) by
number of boats (343) in the shrimping fleet.
Energy in Fuel = 1200 I/day 160 days 3.75 E7 J/l = 7.2 E12 Joules.

2. Miscellaneous Goods and Services = 7.4 E6 pesos/boat/month of operation, about 83 % of which is fuel costs.
Misc. costs = 7.4 E6 peso 5.33 mo = (3.95 E7 peso)/(600 peso/$) = $6.6 E4/yr.

3. Salary = 1.12 E6 peso/ton of catch. Average catch per boat is 8.95 tons per season (see footnote 6).
Total Salary = 1.12 E6 peso/ton 8.95 tons/yr = (1.0 E7 peso)/(600 peso/$) = $1.7 E4.

4. Boat Replacement. Boat costs 98 E6 peso (1985) and has an expected life of 20 years, and is used 1/2 of the fishing
year for shrimp.
Boat Replacement = (98 E6 peso 0.5)/20 yrs = (2.5 E6 peso)/(600 peso/$) = $4.1 E3/yr.

5. Engine Replacement. Engine costs 20 E6 peso (1985) and has an expected life of 4 years and is used 1/2 of the
fishing year for shrimp.
Eng. Replacement = (20 E6 peso 0.5)/4 yrs = (2.5 E6 peso/yr)/(600 peso/$) = $4.1 E3/yr.

6. Shrimp harvest. From data collected by Delegacion Federal de Pesca En Sonora, Departamento de Flota E
Industria, Guaymas Sonora, Mexico, for the year 1984-1985. Total shrimp catch = 3.07 E6 Kg. Total number of
boats = 343. (Dry weight is 20% of wet weight.)
*Average catch/boat = (3.07 E6 Kg)/343 = 9.0 E3 kg wet wt/boat.
Energy in shrimp = 9.0 E6 g 0.2 5 cal/g 4186 J/Cal = 3.8 E10 J/yr.


General Note: Data from interview of Pangas Fishermen, July 1986. Generally the shrimp season is 3 months (Sept.,
Oct., & Nov.). During this time they fish approximately 70 days, harvesting an average of 60 Kg/day of shrimp.

1. Fuel use estimated as 25 I/day on a slow day, and 90 I/day on a good day. Assume average of 40 I/day.
90 days 40 I/day 3.75 E7 J/l = 1.35 Ell J/season.

2. Miscellaneous Goods and Services is the dollar costs of fuel, net, and incidental expenses. Incidental expenses were
calculated as difference between boat and motor replacement costs and money allocated to boat (see footnotes 3, 4,
and 5). Dollar costs of fuel were as follows:
Fuel = 3600 1/yr $0.155/1 = $558.

Dollar costs of net were calculated using cost of net and useful life as follows:
Net = 250,000 peso/2 yrs = (125,000 peso)/(600 peso/$) = $208.

Incidental expenses are difference between boat allocation (.33 of $4.2 E3 = $1400) and fuel and net costs, and
boat and engine costs as follows:
Incidental expenses = $1200 (698 + 208) (50 + 271) = $113.

3. Salary is equal to 2/3 of total value of catch. Total value is distributed as follows: 1/3 to boat, 1/3 to Owner, and
1/3 to helper(s).
Total catch value = 3.6 E3 Kg 600 peso/Kg
= (2.16 E6 peso)/(600 peso/$) = $3.6 E3/season.
Salary = $3.6 E3 0.667 = $2,400.00.

4. Boat replacement costs were estimated using a new boat cost of 600,000 pesos, an average life span of 5 years and
25% of use per year for shrimp season.
Boat replacement = 600,000 peso/5 yrs 0.25 = (3 E4 peso/yr)/(600 peso/$) = $50/season.

5. Engine replacement costs were estimated using new engine costs of 1.3 E6 peso, 2 year life span and 25% of use
per year for the shrimp season.
Engine replacement = 1.3 E6 peso/2 yrs 0.25 = (1.625 E5 peso)/(600 peso/$) = $271.

6. Average catch is 30 Kg/day wet weight during season, assume dry weight is 20% of wet weight.
Energy in shrimp = 30 Kg/day 0.2 90 days 5 Cal/g 4186 J/Cal 1 E3 g/Kg = 1.1 E10 J.


Storages and Gross Flows:

1. Volume of Sea of Cortez (average depth approximately 450 m [Roden, 1958]).
78700 km2 .45 km (1 E9 m3)/km' = 3.54 E13 m3.

Tidal prism exchange: 109 cm 78700 km2 1 E-2 m/cm 1 E6 n2/km2
.5 706 tides/yr = 30.300 E9 m'/yr.

Evaporation: 2.5 m/yr 7.87 E10 m2 = 196.75 E9 m'/yr

Net tidal prism exchange is excess of evaporation, 197 E9 m3/yr minus inflows (river, 18.4
E9; rain 10 E9; other inflow, 3.9 E9) m3/yr = 164.7E 9 m3/yr.

2. Organic Matter (average concentration 1.5 gm C/mn [Mann, 1982]).

Storage: 1.5 gm C/m2 1.724 gm OM/gm C 3.54 E13 m3 = 9.15 E13.

River (1920s; see Footnotes to Tables 2-5, No. 8):
180 E6 T/yr .27 .05 1 E6 gm/T = 2430 E9 gm/yr.

Other runoff (1920s; see Footnotes to Tables 2-5, No. 8):
30 E6 T/yr .27 .05 1 E6 gm/T = 405 E9 gm/yr.

Rain (1920s; see Footnotes to Tables 2-5, No. 12):
1.0 gm/m3 1.72 g OM/gm C 9.92 E9 m3/yr = 17 E9 gm/yr.

Net tidal inflow (1920s; see Footnotes to Tables 2-5, No. 10):
1.5 gm C/m3 1.72 g OM/gm C 164.7 E9 m3/yr = 425 E9 g/yr.

Tidal exchange: (30,300 E9 m'/yr 1.5 gC/m3 1.72 gO.M./gC = 78,174 E9 g/yr.

Inflow = 425 E9 g/yr + 78,174 g/y = 78,599 g/yr

Outflow = concentration volume of water
1.5 gC/m3 1.72 gO.M./gC 30,300 E9 m3/y = 78,174

Production: (see footnotes to Tables 2-5, No.9).
7.87 E10 m2 1.23 gC/m2/d. 365 d. 1.72g O.M./gC = 60,772 E9 gO.M./yr.

Consumption: assume equal to production.

3. Phosphorus (average concentration approximately 1.8 AM [Alvarez-Borrego, 1983]).
1.8 pM (1 E3 L)/m3 (1 E-6 mole)//Mole 95 gm/mole = .17 gm/m3.

Storage: .17 gm/m3 3.54 E13 m3 = 6.0 E12 gm.

River (1920s; see Footnotes to Tables 2-5, No. 11): 2.4 E9 gm/yr.

Footnotes to Figures 7 and 8 (continued).

3. Phosphorus continued.

Other Runoff (1920s; see Footnotes to Tables 2-5, No. 11): 5.1 E8 gm/yr.

Rain (1920s; see Footnotes to Tables 2-5, No. 12): 5.95 E8 gm/yr.

Tidal prism exchange:

Inflow = volume of water integrated concentration of PO4 in flowing water (1.8 jLM)
30,464 E9 m/yr. 1.8 /M 1E3 L/m3 1E-6 Mole/tMole 95 gm/Mole
= 5209 E9 gm/yr.

Outflow = volume of water concentration of P04
30,300 E9 m3/y 1.8 IM 1E3 L/m3 1E-6 Mole/pMole 95 gm/Mole
= 5181 E9 gm/yr.

Sedimentation: assume 1% of CaCO3 deposition rate (1.5 gm/cm2 per 103 years; Broecker and Peng, 1987).
1.5 gm/cm2 1E4 cm2/m2 7.87 E10 m2 1E-3 yrs. 0.01
= 11.8 E9 gmP./yr.

Production: assume 1% of organic matter production
60,772 E9 gm O.M./yr 0.01 = 608 gm P/yr.

Consumption: assume equal production

4. Nitrate (Alvarez-Borrego, 1983).

13 jzM NO3 (1 E3 L)/m3 (1 E-6 mole)/pxmole 62 gm/mole = .81 gm/n3.

Storage: 0.81 gm/m3 3.54 E13 m3 = 2.87 E13 gm.

River (1920s; see Footnotes to Tables 2-5, No. 11): 34.9 E9 gm/yr.

Other Runoff (1920s; see Footnotes to Tables 2-5, No. 11): 7.41 E9 gm/yr.

Rain (1920s; see Footnotes to Tables 2-5, No. 12): 2.08 E9 gm/yr.

Tidal prism exchange:

Inflow = volume of water concentration of NO, in inflowing water (13 /AM).
30,464 E9 m3/yr 0.81 gm/m3 = 24,675 E9 gm/yr.

Outflow = volume of water concentration.
30,300 E9 m'/yr 0.81 gm/m3 = 24,543 E9 gm/yr.

Production: assume 10% of organic matter production
60,772 E9 gm O.M./y 0.10 = 6077 gm NO3/yr.

Consumption: assume equal to production.


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