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Technical Paper No. 38
HUME LIBRARY
APR 11 1o
LF.A.S.- Univ. of Florird
Cut vs
Survival
Hooked
in the
and Growth
Commercial
Florida Keys
of
Sponges
by
John Stevely
and
Don Sweat
FLORIDA SEA GRANT COLLEGE
OR
SURVIVAL AND GROWTH OF CUT
VS.
HOOKED COMMERCIAL SPONGES IN THE FLORIDA KEYS
John Stevely and Don Sweat
Florida Sea Grant Extension Program
117 Newins-Ziegler Hall
University of Florida
Gainesville, FL 32611
Project No. IR-82-15
Grant No. NA80AA-D-00038
Technical Papers are duplicated in limited quantities for specialized
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Program. Content is the sole responsibility of the author. This paper was
developed by the Florida Sea Grant College Program with support from NOAA
Office of Sea Grant, U.S. Department of Cmnnerce, grant number
NA80AA-D-00038. It was published by the Sea Grant Extension Program which
functions as a component of the Florida Cooperative Extension Service, John
T. Woeste, Dean, in conducting Cooperative Extension work in Agriculture,
Home Economics, and marine Sciences, State of Florida, U.S. Department of
Commerce, and Boards of County Commissioners, cooperating. Printed and
distributed in furtherance of the Acts of Congress of May 8 and June 14,
1914. The Florida Sea Grant College is an Equal Employment-Affirmative
Action employer authorized to provide research, educational information and
other services only to individuals and institutions that function without
regard to race, color, sex, or national origin.
TECHNICAL PAPER NO. 38
September 1985
INTRODUCTION
Until the 1940's, the sponge fishery was one of the most valuable
fisheries in Florida. However, a combination of the sponge blights of 1939
and 1946 and the introduction of synthetic sponges resulted in reduction of
the fishery to a small fraction of its former importance (Stevely, et al.,
1978). In recent years, increasing scarcity of sponges in the sponge beds off
of Tarpon Springs has threatened the continued existence of the remaining
Tarpon Springs sponge fleet.
Although an exploratory sponge fishing survey of state territorial waters
off of Monroe County (Florida Keys), Florida, had indicated that commercial
quantities of sponges were present (Sweat and Stevely, unpublished man-
uscript), Florida Statute (F.S. 370.17) prohibits use of "deep sea diving
apparatus to harvest sponges in this area." This Statute states, "No person
may use diving suits, helmets, or other apparatus used by deep sea divers in
taking commercial sponges from any waters within the territorial limits of
this state."
The purpose of the law was not to prohibit reasonable methods of
harvesting sponges but to protect young sponges. It was enacted to prevent
damage to young sponges caused by heavily weighted divers stepping on them.
Early sponge diving gear was of the deep sea variety. Scuba and hookah,
common gear today, did not become a viable method of extended underwater
diving until many years after enactment of the law. Light hookah gear with
rubber-soled, canvas athletic shoes has now replaced the heavy helmet and lead
boot-clad diver.
The Florida Saltwater Fisheries Study and Advisory Committee recommended
in 1982 that sponge diving be allowed in the state territorial waters off
Monroe County. However, objections were raised concerning the possibility of
overfishing due to increased fishing pressure following legalization of sponge
diving. Therefore, the present project was undertaken for the purpose of
establishing whether a change in harvesting technique -- cutting rather than
tearing the sponge loose -- could insure sponge regeneration and thus reduce
the possibility of overfishing. Sponges have remarkable regenerative ability;
and if even a small quantity of sponge material is left attached to the
substrate, the sponge may survive and grow back to a commercially valuable
size.
METHODS AND MATERIALS
During June, 1982, a commercial sponge fisherman assisted the project
by locating a bed of sheepswool sponges (Hippiospongia lachne) off of Vaca Key
(Marathon) in the Florida keys (Fig. 1). The site was marked with a buoy, and
Loran C coordinates were recorded to insure relocation of the study site. The
bottom of the site was marked off by laying out a grid of polyethylene line
held in.place-by rebar stakes driven into the substrate. Sponges were located
by swimming along the grid lines. Upon locating a sponge, its position was
marked by attaching a piece of brightly colored surveyor's flagging tape to
the line. The position was also recorded on a plastic chart of the grid
pattern. Large calipers (S & S standard radiological) were used to take two
measurements of the sponge's diameter and one measurement of the sponge's
height.
After being measured, alternate sponges were either cut loose using
a large, sharp knife or torn loose with a sponge hook on the end of a three-
foot handle. Sponges were cut as close to the substrate as possible while
attempting to leave a complete sponge base. In practice, this left 1/2 to 1
Monroe County. However, objections were raised concerning the possibility of
overfishing due to increased fishing pressure following legalization of sponge
diving. Therefore, the present project was undertaken for the purpose of
establishing whether a change in harvesting technique -- cutting rather than
tearing the sponge loose -- could insure sponge regeneration and thus reduce
the possibility of overfishing. Sponges have remarkable regenerative ability;
and if even a small quantity of sponge material is left attached to the
substrate, the sponge may survive and grow back to a commercially valuable
size.
METHODS AND MATERIALS
During June, 1982, a commercial sponge fisherman assisted the project
by locating a bed of sheepswool sponges (Hippiospongia lachne) off of Vaca Key
(Marathon) in the Florida keys (Fig. 1). The site was marked with a buoy, and
Loran C coordinates were recorded to insure relocation of the study site. The
bottom of the site was marked off by laying out a grid of polyethylene line
held in.place-by rebar stakes driven into the substrate. Sponges were located
by swimming along the grid lines. Upon locating a sponge, its position was
marked by attaching a piece of brightly colored surveyor's flagging tape to
the line. The position was also recorded on a plastic chart of the grid
pattern. Large calipers (S & S standard radiological) were used to take two
measurements of the sponge's diameter and one measurement of the sponge's
height.
After being measured, alternate sponges were either cut loose using
a large, sharp knife or torn loose with a sponge hook on the end of a three-
foot handle. Sponges were cut as close to the substrate as possible while
attempting to leave a complete sponge base. In practice, this left 1/2 to 1
inch of sponge tissue. The sponge hook was of the type used by commercial
sponge divers. When the sponge was removed, the type of harvesting method
used was recorded and measurements taken of the remaining sponge base (if
there was any left). The exact location of each sponge was marked by driving
Figure 1.
0, c, \
Sponge
\ Sites 7
Study Area
,, 1. 9 / *7
/ 'r /4
\ Ir SM 3 7
9** 9 B.r
6. .
a1 61 S" Kw...t
0 6 5 2 2 2
8 2
.- s\ S> 29 S 22 \ .
WSJ a 38 2 C.
"ia^ "^!^^3_^^ l ^/C-1^ ,^7^^ .6 ^ 3^ *>3^ 0>
a rebar stake into the substrate. A numbered, plastic bird band was wrapped
around these stakes for identification. Also, in those cases where sponge
base was left behind, the sponge base was marked by "sewing" a piece of
monofilament line through it and then attaching a plastic bird band. Ten
sponges were staked and tagged to serve as a control group. Growth and
survival data for experimental and control sponges were collected 12 months
(May '83) and 28 months (Nov. '84) after the study was begun.
RESULTS
Survival of Cut and Hooked Sponges
A total of 69 sponges were either cut (N=35) or hooked (N=34).
Approximately one-third of all the study sponges (control, cut, hooked) were
not found by the end of the experiment for a variety of reasons which are
discussed (Fig. 2). The percentages of found sponges for each group of
sponges were not significantly different (G-test; Sokal and Rohlf, 1969).
Twelve months after the study began, 70% of the found cut sponges were
alive and 39% of the found hooked sponges were alive (Fig.3). The percentage
of surviving cut sponges compared to that of surviving hooked sponges was
significantly different (G-test; P<.05).
Twenty-eight months after the study began, 71% of the found cut sponges
were alive and 41% of the found hooked sponges were alive (Fig. 3). Again,
the proportion of surviving sponges between the treatments was significantly
different (G-test; P<.05).
The slightly higher percentage of surviving cut and hooked sponges
found at 28 months compared to 12 months was not significantly different and
can be attributed to sampling error. Since fewer sponge sites were found at
28 months (Fig. 2.), the sample size used to calculate percentages of
surviving sponges was smaller (number of found cut and hooked sponge sites
was 55 at 12 months and 47 at 28 months).
On both sampling dates, 100% of the found control sponges were alive.
The percentage of surviving found control sponges was significantly different
from the percentage of surviving found cut and hooked sponges (G-test; P<.05).
Growth of Experimental and Control Sponges
Average increase of the maximum diameter of the cut sponge bas was 2.3
cm. (range: -1.5 to 5.0 cm.) after 28 months. Average increase of the maximum
diameter of the hooked sponge base was 2.1 cm. (range 0.0 to 4.00).
Only a small number of surviving cut sponges (7, or 39%) and hooked
sponges (3, or 33%) were judged to have regrown to a commercial size. Whether
sponges had or had not grown to a commercially harvestable size was a qual-
itative judgement. Although most of the surviving sponge bases had grown to
the point of exceeding 12.7 cm. (to be legal size a sponge must have, when
wet, a maximum diameter of at least 12.7 cm), they had not yet grown in height
sufficiently enough to be judged as a truly commercially valuable product by
the authors. Therefore, only sponges which could be crudely estimated to have
attained a height of at least 7.6 cm. were considered as commercial-sized
sponges. However, there is no legal requirement for a minimum sponge height.
The average natural growth rate of control sponges monitored during the
study (7 of the 10 original controls were found at the end of the study) was
1.7 cm./year.
a rebar stake into the substrate. A numbered, plastic bird band was wrapped
around these stakes for identification. Also, in those cases where sponge
base was left behind, the sponge base was marked by "sewing" a piece of
monofilament line through it and then attaching a plastic bird band. Ten
sponges were staked and tagged to serve as a control group. Growth and
survival data for experimental and control sponges were collected 12 months
(May '83) and 28 months (Nov. '84) after the study was begun.
RESULTS
Survival of Cut and Hooked Sponges
A total of 69 sponges were either cut (N=35) or hooked (N=34).
Approximately one-third of all the study sponges (control, cut, hooked) were
not found by the end of the experiment for a variety of reasons which are
discussed (Fig. 2). The percentages of found sponges for each group of
sponges were not significantly different (G-test; Sokal and Rohlf, 1969).
Twelve months after the study began, 70% of the found cut sponges were
alive and 39% of the found hooked sponges were alive (Fig.3). The percentage
of surviving cut sponges compared to that of surviving hooked sponges was
significantly different (G-test; P<.05).
Twenty-eight months after the study began, 71% of the found cut sponges
were alive and 41% of the found hooked sponges were alive (Fig. 3). Again,
the proportion of surviving sponges between the treatments was significantly
different (G-test; P<.05).
The slightly higher percentage of surviving cut and hooked sponges
found at 28 months compared to 12 months was not significantly different and
can be attributed to sampling error. Since fewer sponge sites were found at
28 months (Fig. 2.), the sample size used to calculate percentages of
DISCUSSION
Survival of Cut and Hooked Sponges
This study shows that both cut and hooked sponges can successfully regrow
to a commercially harvestable size. However, cut sponges have a substantially
higher chance for survival and consequently have a higher chance for regrowth
to a commercial size than do hooked sponges. The higher survival rate of cut
sponges can be attributed to the fact that cutting insures that some sponge
tissue is left attached to the substrate. Sponge tissue is sometimes left
behind when hooking the sponge; but often when the sponge is torn free, very
little tissue is left. If sufficient sponge tissue is not left, sediment can
easily smother the remaining sponge tissue.
It is probable that higher survival of cut sponges than that recorded in
this study could be realized if the sponges were cut so that a taller sponge
base was left behind, reducing the chances of the sponge being smothered by
sediment. However, this is economically impractical for a commercial sponger
at the present time since leaving an additional 3 to 5 cm. of sponge tissue
would substantially reduce the value of the harvested sponge. On the other
hand, the base of most sponges is embedded with rock and foreign material and
normally is trimmed and discarded before retail sale, so an educational,
voluntary program directed at sponge producers and buyers might be helpful.
Any management technique based on the requirement to leave a minimum height
would be unenforceable since it is impossible to determine at what level a
harvested sponge was cut.
If it is assumed that all "lost" sponges represent mortality due
to experimental treatment (cutting or hooking) then the survival of all
experimental sponges would be lower than that observed for only sponges (or
Figure 2.
Percentage of sponge sites found, (number of
sponge sites found/total number of sponge sites)
x 100, May 1983 and Nov. 1984.
100%-
90%-
80%-
70%-
60%-
50%-
40%-
30%-
20%-
10%-
MAY
1983
Rfln
70%
ITT
CONTROL
N-10
NOV.
1984
82%
77%
71%
1T]
65%
HOOKED
N-34
---~-
Figure 3.
Percentage of sponges found which survived,
(number living sponges/number sponge sites
found) x 100, May 1983 and Nov. 1984.
100% 100%100% Eli
M10 MAY NOV.
90%1983 1984
90%-
| 80%-
0 70% 71%
q 70%-
S60%-
50%
0 40 '41%
0 40%-
S 20%
10%-
CONTROL CUT HOOKED
N-10 N-35 N-34
the stakes marking their positions) which were found. Complete mortality
of "lost" sponges was not deemed likely by the authors for the following
reasons: 1) a similar portion (30%) of the control sponges were "lost"
compared to the experimental sponges; 2) the sponges were widely scattered
over a large area; and with the limitations of underwater visibility, it was
impossible to locate all sponges; 3) at times the area was heavily fished by
lobster trap fishermen and a number of marker stakes could have been
inadvertently dislodged by traps.
Therefore, a maximum estimate of survival would be 71% for cut sponges
and 41% for hooked sponges based on data on found experimental sponge sites
(N=47). A minimum estimate of survival would be 51% for cut sponges and 26%
for hooked sponges based on number of sponges in the initial experimental
group (N=69).
Growth of Experimental and Control Sponges
The results of this study demonstrate that at least 2 years are required
for the surviving sponge base to regrow to a minimum commercial size. The
observed growth rate would indicate that 1 or 2 additional years would be
desirable to insure that a higher percentage of sponges attained harvestable
size. The additional time would also allow the sponges to grow to a larger
and thus more valuable size.
Historically, several studies of sheepswool sponge growth (Moore,
1910; Crawshay, 1939; Storr, 1964) have measured sponge growth in terms of
volumetric increases (the number of times a sponge increases in volume during
a 1-year period). Variability in sponge shape and repeated attempts to obtain
reproducible measurements of sponge height were such that volumetric estimates
of sponge size were judged to be inappropriate. Therefore, in this study,
sponge growth was expressed in terms of increase in the maximum sponge
diameter. Based on repeated measurements of several sponges conducted at the
study's beginning, the maximum sponge diameter was the only measurement found
to be reproducible within 0.5 cm. These observations have been confirmed in
a recent study of sponge growth in Biscayne Bay, Florida (pers. comm., J.
Tilmant; Everglades National Park, Homestead, FL).
Although direct comparison is difficult, growth of control sponges
in this study appears to be somewhat slower than that recorded in older
studies. Storr (1964) measured a growth factor of 2.27 (number of times a
sponge increases in volume during a 1-year period) for sheepswool sponges
from Piney Point, Florida. Based on this growth rate, Storr estimated it
would require at least 3 years to reach a harvestable size. Moore (1910)
studied sheepswool sponge growth at Anclote Key and Sugarloaf Key, Florida,
and measured growth factors lower than Storr's data (1.91 and 1.86 respec-
tively). Smith (1973) studied a different species of commercial sponge, the
grass sponge (Spongia graminea), in Card Sound, Florida, and reported a growth
factor of 0.77. Studies of sheepswool sponges in the Bahamas and British
Honduras (Crawshay, 1939) found growth rates of 2.34 to 2.94.
Tilmant (pers. comm.) working on sheepswool sponge growth rate in
Biscayne Bay, Florida, reported a 2.0 cm./year increase in diameter. This
growth rate would produce a commercial sponge in approximately 6.4 years. The
growth rate measured in this study of 1.7 cm./year would produce a commercial
sponge in 7.5 years.
The variability of sheepswool sponge growth rates from different
locations is noted in the literature (Stevely, et al., 1978). Substantial
differences in growth rates of commercial grass sponges (Spongia graminea)
located on the same rock outcropping have been reported (Smith, 1973). It
is possible that this study was located in an area not conducive for rapid
sponge growth. However, sponges in the area were abundant and appeared to
be in healthy condition. Sponge fishermen were seen working the general area,
although most sponging activity was conducted closer to Vaca Key in shallower
water. Therefore, it seems reasonable to assume that the study site was
representative of commercially productive sponge bottom.
CONCLUSIONS
1. Sponge tissue left attached to the substrate after the sponge has been
harvested by either cutting or hooking can survive and grow.
2. Survival of remaining sponge tissue is substantially greater when sponges
are harvested by cutting compared to those sponges harvested by hooking, since
cutting insured that more regenerative sponge tissue was left attached to the
substrate.
3. The maximum estimate of sponge survival for cut sponges is 71% and
for hooked sponges is 41%. The minimum estimate of sponge survival for cut
sponges is 51% and for hooked sponges is 26%.
4. At least 2 years is required for surviving sponge tissue to regrow to
a commercially harvestable size. An additional 1 or 2 years is required for
more sponges to attain a more valuable size.
5. Any attempted management of the sponge fishery requiring, by statute,
a minimum height requirement to be left when cutting a sponge would be
unenforceable, and that this "recommendation" could be better addressed by
an educational program directed at both sponge producers and buyers.
located on the same rock outcropping have been reported (Smith, 1973). It
is possible that this study was located in an area not conducive for rapid
sponge growth. However, sponges in the area were abundant and appeared to
be in healthy condition. Sponge fishermen were seen working the general area,
although most sponging activity was conducted closer to Vaca Key in shallower
water. Therefore, it seems reasonable to assume that the study site was
representative of commercially productive sponge bottom.
CONCLUSIONS
1. Sponge tissue left attached to the substrate after the sponge has been
harvested by either cutting or hooking can survive and grow.
2. Survival of remaining sponge tissue is substantially greater when sponges
are harvested by cutting compared to those sponges harvested by hooking, since
cutting insured that more regenerative sponge tissue was left attached to the
substrate.
3. The maximum estimate of sponge survival for cut sponges is 71% and
for hooked sponges is 41%. The minimum estimate of sponge survival for cut
sponges is 51% and for hooked sponges is 26%.
4. At least 2 years is required for surviving sponge tissue to regrow to
a commercially harvestable size. An additional 1 or 2 years is required for
more sponges to attain a more valuable size.
5. Any attempted management of the sponge fishery requiring, by statute,
a minimum height requirement to be left when cutting a sponge would be
unenforceable, and that this "recommendation" could be better addressed by
an educational program directed at both sponge producers and buyers.
LITERATURE CITED
CRAWSHAY, L. R., 1939. Studies in the market sponges. 1. Growth from the
planted cutting. Jour. Mar. Biol. Assn. of the U.K. 23:553-574.
MOORE, H. F., 1910. The commercial sponges and the sponge fisheries. Bull.
U.S. Bur. Fish., Vol. 28, Part 1, 1908:399-511.
SOKAL, R. R., and F. J. ROHLF, 1969. Biometry: The principles and
practice of statistics in biological research. W. H. Freeman and Company,
San Francisco. 776 pp.
SMITH, R. L., 1973. Abundance and diversity of sponges and growth rates of
Spongia graminea in Card Sound, Florida. Master's Thesis, Univ. Miami, Coral
Gables, Florida. 66 pp.
STEVELY, J. M., J. C. THOMPSON and R. E. WARNER, 1978. The biology and
utilization of Florida's commerical sponges. Florida Sea Grant College
Program Tech. Rept. No. 8. 45 pp.
STORR, J. F. 1964. Ecology of the Gulf of Mexico commercial sponges and its
relation to the fishery. U.S. Dept. Interior, Fish. Wild. Serv., Spec. Sci.
Rept. No. 4666:1-73.
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