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Title: Assessment of conch densities in backreef embayments on the northeast and southeast coast of St. Croix, U.S. Virgin Islands
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Title: Assessment of conch densities in backreef embayments on the northeast and southeast coast of St. Croix, U.S. Virgin Islands
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Creator: Tobias, William
Publisher: Division of Fish and Wildlife, Department of Planning and Natural Resources
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SEAMAP-C FY-2004 Supplemental
St Croix BackreefEmbayment Conch Assessment
Final Report





Report

to the

Southeast Area Monitoring and Assessment Program Caribbean
(SEAMAP-C)


State


: United States Virgin Islands


Project Number

Study Number

Study Title


Report Written By




Date of Report

Project Staff




Report Reviewed By


: NA03NMF4350100

:3

: Assessment of Conch Densities in Backreef Embayments on
the northeast and southeast coast of St. Croix, U.S. Virgin
Islands.

: William Tobias, Fish and Wildlife Biologist ITI
Department of Planning and Natural Resources
Division of Fish and Wildlife
U.S. Virgin Islands

: January 20, 2005

: William Tobias, Fish and Wildlife Biologist III
Ivan Mateo, Fisheries Biologist II (resigned 2001)
Jennifer Valiulis, Fisheries Assistant (departed 2005)
Christine O'Sullivan, Fisheries Biologist I (resigned 2005)

: Barbara Kojis, Ph.D., Director
K. Roger Uwate, Ph.D., Chief of Fisheries
Shenell Gordon, Fisheries Biologist I
Monica Valle-Esquivel, Ph.D., University of Miami
Wes Toller, Ph.D., Fisheries Biologist III






SEAMAP-C FY-2004 Supplemental 2
St. Croix Backreef Embayment Conch Assessment
Final Report

SUMMARY

Data on conch abundance, density and habitat type were collected in six shallow backreef
embayments (1 to 7 m in depth) on St. Croix, three on the northeast coast (Cottongarden Bay,
Teague Bay and YellowcliffBay) from October 1998 to September 1999, and three on the
southeast coast (Turner Hole Bay, Robin Bay and Great Pond Bay) from July 2000 to September
2001. The conch data were collected as a secondary objective in determining the importance of
backreefembayments as fisheries nursery grounds (Mateo and Tobias 2001 and 2004). This
report analyzes the conch data collected and compares conch abundance, density and habitat type
in the six embayments.

The total conch density for the combined northeast (7.75 ha) and southeast (6.78 ha)
embayments was 43.8 conch/ha. Total conch density was higher in the northeast embayments
(52.6 conch/ha) than in the southeast embayments (33.6 conch/ha). Mean density of measured
conch less than legal harvestable size (<22.8 cm) from all bays was 32.9 conch/ha (SD = 15.13).
Mean density of measured conch of harvestable size (>22.8 cm) from all bays was 4.7 conch/ha
(SD = 2.65). Significant differences were found between embayments. Adult conch densities
were extremely low for reproduction (Stoner and Ray 1996).

The backreef embayments studied were found to contain predominately juvenile conch. Length-
frequency data show a mean conch size in all bays of 17.1 cm (SD = 1.21); 87% of the conch
measured were less than legal harvestable size (>22.8 cm).

Seagrass (Thalassia testudinum and Syringodiumfiliforme) was the dominant habitat type found
in the six embayments. A total of 98% of all conch observed were recorded in sand, algal plain
and seagrass habitats or combinations thereof Of this total, 79% of all conch <22.8 cm and 63%
of all conch >22.8 cm were found in seagrass or seagrass combination habitats. The substantial
numbers of juvenile conch found in seagrass habitats indicates that the backreef embayments
serve as important nursery habitat.

The bank-barrier reef structure may also be a physical barrier to the movement and
inshore/offshore migration of conch. This barrier effect could artificially enhance the numbers
of adult conch found within the embayments, if conch movement is restricted. This could
facilitate locating and harvesting of these resources.

Both juvenile and adult conch densities were lowest in Cottongarden Bay on the northeast coast.
On the southeast coast, Robin Bay and Great Pond Bay juvenile densities were low and adult
conch densities in all three southeast bays were uniformly low. These low conch densities may
be the result of an illegal and undocumented harvest, which targets legal as well as undersized
conch both in and out of season. Pressure on the resource may be greater in more geographically
isolated, unpopulated coastal areas with limited shoreline access.

Additional conch research in these embayments is recommended. Specific study topics include:
recruitment of conch larvae; currents/hydrodynamics within the bays; habitat for juvenile conch
<7.0 cm; habitat identification where conch were found during census surveys; conch lip







SEAMAP-C FY.2004 Supplemental 3
St Croix Backreef Embayment Conch Assessment
Final Report

measurements; conch tagging studies to identify movement; shoreline surveys to determine
recreational conch harvest; and seasonal abundance and distribution of conch egg masses.

It is also recommended that adult conch be seeded in protected "No-Take"embayments in the
East End Marine Park to increase inshore stock abundance. Also, enforcement of existing conch
regulations is needed.






SEAMAP-C FY-2004 Supplemental 4
St. Croix Backreef Embayment Conch Assessment
Final Report
INTRODUCTION

Queen conch (Strombus gigas) is a large marine gastropod found in the Caribbean Sea and
tropical Western Atlantic, ranging from Bermuda to northern Brazil (Valle-Esquivel 2002a).
The depth range of queen conch is from shallow subtidal waters to 76 m (Chakalall and
Cochrane 1996). Conch are benthic grazers, feeding on macroscopic and unicellular algae and
detritus where clear water and sandy substrate support algae and seagrass production (Valle-
Esquival 2002a; and Chakalall and Cochrane 1996). Preferred habitats for conch are shallower
than 18 to 24 m and include seagrass and sandy algal beds, gravel, coral rubble, smooth hard
coral and beach rock bottoms (CFMC 1996). Conch densities decrease significantly below 30 m
due to light limitations for plant growth (Randall 1964). Overfishing continues to deplete
available stocks throughout its range, reducing the economic importance of a once highly
valuable commercial resource (Appeldoorn and Rodriguez 1994).

Dammann (1969) and Clavijo et al. (1986) reported that the conch fishery was the third most
important fishery, behind fish and lobster, in the U.S. Virgin Islands. Available habitat to
support the conch fishery is limited to waters of the surrounding shallow insular shelf platform.
The approximate size of this habitat is estimated to be 34,300 ha for St. Croix and 162,925 ha for
St. Thomas and St. John (CFMC 1999). Despite a smaller shelf platform, the majority of conch
landings in the U.S. Virgin Islands are recorded from St. Croix (Tobias 1987; Garcia-Moliner
1997; and Tobias et al. 2000).

Wood and Olsen (1983) determined that the conch resources of the Virgin Islands had been
seriously depleted by the late 1970's. In an effort to uniformly manage conch resources in the
territory, conch regulations were approved in 1994, which established an annual closed season
(July to September), bag limits (150 conch/commercial fisher/day and six conch/recreational
fisher/day, not to exceed 24 conch/boat) and size limits (>22.8 cm total length or 9.5 mm lip
thickness). In addition, regulations required that conch be landed whole in the shell (VIRR
1994; and CFMC 2001) to make enforcement of minimum sizes practicable.

The queen conch fishery around St. Croix is artisanal. Most commercial vessels are outboard-
powered, fiberglass constructed and less than 8 m in length (Kojis 2004). Conch are collected by
hand using scuba or snorkeling gear. Wood and Olsen (1983) calculated the maximum
sustainable yield for conch from St. Croix at 60,000 ibs/yr. Valle-Esquivel (2002b) reported
dramatic changes in St. Croix conch landings since the late sixties, increasing to a maximum of
59,000 lbs in 1979, and fluctuating to a level of 20,000 to 30,000 lbs annually since then.
Rosario (1995) and Rivera (1999) identified 25 and 28 conch fishers, respectively, in their
studies of the commercial conch fishery from St. Croix. Kojis (2004) reported that 215
commercial fishers were registered in St. Croix during the fishing year of July 2003 to June
2004; 84 fishers (39.1%) reported harvesting conch. This suggested that fishing effort for queen
conch has increased while reported commercial landings have remained relatively constant.
Thus, an increased effort has not resulted in a significant increase in landings (Valle-Esquivel
2002a).

Gordon (2002) reported conch densities around St. Croix to be 72.3 juvenile conch/ha and 27.4
adult conch/ha. These density values were higher than in St. Thomas and St. John. The highest






SEAMAP-C FY-2004 Supplemental 5
St Croix Backreef Embayment Conch Assessment
Final Report

mean adult densities were found in the 19 to 24 m depth range. Juvenile conch abundance
decreased with increasing water depth. However, no surveys were conducted in shallow, inshore
waters (0 to 6 m depth range) during this 2001 survey.

This report presents data on conch abundance, density and habitat type in six shallow, backreef
embayments (1 to 7 m depth) on St. Croix, three on the northeast coast (Cottongarden Bay,
Teague Bay and YellowcliffBay) and three on the southeast coast (Turner Hole Bay, Robin Bay
and Great Pond Bay). The conch data presented here was collected secondarily during surveys
of fish communities in these embayments. The results from that study showed the ecological
importance and fishery value of the backreefembayments as nursery ground for recreationally
important finfish species (Mateo and Tobias 2001 and 2004). The presence of queen conch in
these areas, and the importance of this species as a fishery resource and as part of the benthic
community around the U.S. Virgin Islands, motivated field staffto collect detailed information
on presence, location, depth, size and density of conch individuals. A secondary objective of the
original backreef study thus became to collect conch data so that it would be available for later
analyses such as for size distribution, density, and abundance ofjuvenile and adult queen conch
and to characterize their preferred habitat types.


1VETHODOLOGY

Study Area

Six embayments were sampled in this study: Cottongarden Bay (CB), Teague Bay (TB), and
YellowcliffBay (YB) on the northeast coast, and Turner Hole Bay (THB), Robin Bay (RB) and
Great Pond Bay (GPB) on the southeast coast. The bays are part of the nearly continuous bank-
barrier reef system extending from Pull Point to Lamb Point on the northeast coast (commonly
referred to as the Teague Bay bank-barrier reef system) and from East Point to Vagthus Point on
the southeast coast of St. Croix (Figure 1). This extensive reef complex forms a protective
barrier against wind and wave energy for numerous backreef embayments (Mateo and Tobias
2001 and 2004). Embayments range in depth from I meter on their eastern and western
extremes to 7 to 8 m in the interior lagoons. The distance from shore to the bank-barrier reef in
the northeastern embayments varies from 500 to 700 m. The approximate embayment lengths
are 600 m, 1200 m and 900 m for Cottongarden Bay, Teague Bay and Yellowcliff Bay,
respectively. The southeast embayments of Turner Hole and Robin Bay are approximately 300
m wide and 1000 m long. Great Pond Bay, approximately 900 m wide and 2.5 km long, is
bounded on its landward side by a baymouth bar and on the seaward side by a contiguous coral-
algal reef(Bruce et al. 1989).

Burke et al. (1989) and Hubbard (1989) described habitat zonation patterns in embayments on
the northeast and southeast coast, respectively. In general, seagrass (Thalassia testudimnm and
Syringodiumfiliforme form beds of varying density) and sediment-dwelling organisms, such as
mollusks and echinoderms, dominate in the lagoon. Calcareous algal species, including
Halimeda spp. and Penicillus spp., and many other species of macroalgae are abundant in
seagrass beds. Deeper portions of lagoons consist of extensive sandy areas with sparse seagrass
cover. The bottom is extensively hummocked in these areas with sand mounds 10 to 20 cm in






SEAMAP-C FY-2004 Supplemental 6
St Croix BackreefEmbayment Conch Assessment
Final Report

height created by the burrowing shrimp Callianassa spp. An abrupt transition from lagoon to
backreefis marked by scattered coral colonies of Montastraea annularis, Porites astreoides and
Diploria spp., many of which have died since the descriptions of Burke et al. (1989) and
Hubbard (1989).


Survey Method

The transect methodology used to survey conch abundance and density was identical to that used
to survey fish species composition and abundance in these embayments (Mateo and Tobias 2001
and 2004). Monthly sampling was conducted in the northeast embayments from October 1998 to
September 1999 and in the southeast embayments from July 2000 to September 2001. Due to
bad weather and adverse sea conditions; no sampling was conducted during the months of
November 2000 and April 2001. Bad weather and adverse sea conditions also prevented
sampling Great Pond Bay in December 2000 and March 2001 and Robin Bay in December 2000
and August 2001.

For each bay, a 20 x 20 m grid was established over a nautical chart and the intersecting points
were given a consecutive number. Transect locations were then selected using random numbers
from intersecting points on the grid. Ten 50-m transects were randomly selected for location and
direction in each embayment. A weighted transect tape with buoys on each end to identify the
transect from the surface was deployed from a surface vessel while the vessel's captain
maintained the desired compass heading. Upon deploying the transect, two divers entered the
water at the starting point and simultaneously conducted the monthly conch censuses along a 2-
m wide belt transect on either side of the transect line (survey area 100 m2 per diver). When
only one diver was available, surveys were competed by the diver counting conch first on one
side of the transect and then on the other side. All queen conch encountered along the transect
were counted and total shell length (apex of the spire to the end of the siphonal canal) was
measured (mm) with a caliper and recorded.

Information on habitat type was also recorded. Percent habitat cover was estimated from linear
coverage along transects (Mateo and Tobias 2001 and 2004). The proportional composition of
the habitat covered in each transect was estimated by measuring the combined length of the
transect line overlying each substratum type and dividing it by the transect length. The benthic
habitat categories selected were similar to the habitat classification scheme used by the National
Oceanic and Atmospheric Administration's National Ocean Service (Kendall et al. 2001):

Patch reef: isolated, elevated calcareous structure (not part of the contiguous reef) with a
vertical profile that often, but not always contains live coral.
Rubble: low-relief calcareous structure composed primarily of dead/dying coral
fragments that are not attached to the substrate.
Sand: areas of open sand with very little or no (<10% cover) plants or coralline material
represented.
Algal plain: sand bottom dominated by Dictyota spp., Halimeda spp., and/or Udotea
spp., which may include sparse stands ofS. filiforme and T. testudimim.





SEAMAP-C FY-2004 Supplemental
St Croix Backreef Embayntent Conch Assessment
Final Report

Seagrass: monospecific or nearly moni
varying densities of S. filiforme.

The data collected were used to determine con
categories, total conch density, frequency of c
embayments. From October 1998 to February
embayments were not directly measured but re
and >200 mm). These data were omitted from
calculations of total conch density. All conch i
measured. Total conch density data were tested
Normality test and the Levene Median Test wi
data failed the normality test even after log (x
non-parametric statistics were used to analyze
ranks for unequal sample size was used to test
conch density. A Dunn's All Pairwise Multiplh
among embayments, following a probability ad


RESULTS

The total number of conch observed and total,
embayments on St. Croix in September 1998 t,
respectively, is shown in Table 1. A total of 6:
on the northeast coast and 228 on the southea&
14.53 hectares of bottom habitat, 7.75 ha in th
southeast embayments. The total conch density
embayments was 43.8 conch/ha. Total conch I
(52.6 conch/ha) than in the southeast embaymi

Table 2 shows the summary of conch number,
embayments on St. Croix in September 1998 t,
respectively. Northeast embayments averaged
conch/embayment. Of the conch measured in:
were <22.8 cm and 14.3 conch/embayment we

Southeast embayments averaged 226 transects
were measured in southern embayments. Ther
cm and 8.7 conch/embayment > 22.8 cm.

The number of conch observed and area survey;
St. Croix is shown in Table 3. A total of 775
embayments, 278 in Cottongarden Bay (2.78 1
YellowcliffBay (2.37 ha). The most conch w(
conch/100 m2) and the fewest conch in Cotton
YellowcliffBav had 133 conch (0.56 conch/I C


7


specific stands of T. testudimrm, mixed with


i length-frequencies, conch densities by size
ch by habitat type and by size for each of the six
999, some of the conch in the northeastern
Irded in size categories (<100 mm, 100-200 mm
onch length-frequency plots but included in
the southeast embayments were individually
for normality using a Kolmogorov-Lilliefors
used to test equal variance (Zar 1984). If the
.) transformation and the equal variance test,
ie data. A Kruskall-Wallis One-way ANOVA on
ir significant differences among embayments for
Comparison test was used to test for differences
stment for the number of comparisons.




inch density in the northeast and southeast
October 1999 and July 2000 to September 2001,
I conch were observed in the embayments, 408
coast. The combined survey area comprised
northeast embayments and 6.78 ha in the
for the combined northeast and southeast
asity was higher in the northeast embayments
ts (33.6 conch/ha).

d density in the northeast and southeast
October 1999 and July 2000 to September 2001,
58.3 transects/embayment and 136
irthern embayments, 94.0 conch/embayment
> >22.8 cm.

mbayment and 76 conch/embayment. All conch
was an average of 67.3 conch/embayment <22.8


d in the northeast and southeast embayments on
insects were surveyed in the northeast
), 260 in Teague Bay (2.60 ha) and 237 in
: observed in Teague Bay (170 conch; 0.65
Irden Bay (105 conch; 0.37 conch /100 m2).






SEAMAP-C FY-2004 Supplemental
St. Croix BackreefEEmbayment Conch Assessment
Final Report

A total of 678 transects were conducted in the
Turner Hole Bay (2.51 ha), 208 in Robin Bay (
The most conch were found in Turner Hole Ba
of conch were found in Robin Bay (38 conch; (
0.21/100 m2).

Conch density and conch size (in relation to thi
and southeast embayments are shown in Table
density in Cottongarden Bay was 37.76 conch/
>22.8 cm). Conch density for Teague Bay wa,
5.38 conch/ha > 22.8 cm). Conch density in Y
conch/ha <22.8 cm and 9.70 conch/ha > 22.8 c

In the southeast embayments, Turner Hole Ba)
conch/ha <22.8 cm and 3.98 conch/ha >22.8 ci
conch/ha (15.38 conch/ha <22.8 cm and 2.88 c
Bay was 21.00 conch/ha (16.43 conch/ha < 22

Mean density of conch <22.8 cm (measured cc
15.13) (calculated from Table 4). Mean densit
all bays was 4.7 conch/ha (SD = 2.65). A total
not directly measured and were not included in

A total of 83 conch from the northeast embayn
recorded in three size categories (<100 mm, 1(
were counted in Cottongarden Bay (11 conch
from Teague Bay (6 conch < 100 m, 23 conch
conch from YellowcliffBay (1 conch < 100 rn
mm).

Total conch density data was significantly diffe
way ANOVA, F = 4.878905, P = 0.000197, df
value was adjusted for multiple comparisons ol
Dunn's Method, the data did not show a signify

The length-frequency histogram for all conch f
is shown in Figure 4. A total of 553 conch wei
(minimum legal harvest size) and 12.5% (69 cc

Length-frequency histograms for the conch fou
Bay, Teague Bay and YellowcliffBay are shov
size was 16.5 cm (+/- SD = 3.75 cm); 92% oft
size in Teague Bay was 17.3 cm (+/-SD = 4.32
In YellowcliffBay, mean conch size was 19.2 <
conch were <22.8 cm.


8


autheast embayments (see Table 3), 251 in
08 ha) and 219 in Great Pond Bay (2.19 ha).
(144 conch; 0.57/100 m2). Similar abundances
18/100 m2) and Great Pond Bay (46 conch;


egal harvest size of 22.8 cm) in the northeast
and Figures 2 and 3, respectively. Conch
L (28.40 conch/ha <22.8 cm and 2.27 conch/ha
i5.38 conch/ha (44.23 conch/ha < 22.8 cm and
lowcliffBay was 56.11 conch/ha (38.81
).

onch density was 57.37 conch/ha (53.38
). In Robin Bay, conch density was 18.27
ach/ha >22.8 cm). Conch density in Great Pond
cm and 4.56 conch/ha > 22.8 cm.

;h only) from all bays was 32.9 conch/ha (SD =
of conch >22.8 cm (measured conch only) from
f 83 conch from the northeast embayments were
onch density calculations

nts were counted, but not directly measured, and
-200 mm and > 200 mm). Twenty four conch
100 mm and 13 conch = 100-200 mm), 41 conch
100-200 mm and 12 conch >200 mm) and 18
6 conch = 100-200 mm and 11 conch > 200


nt among embayments (Kruskall-Wallis One-
S5). However, when the probability or alpha
ix embayments and the data retested by the
mt difference among embayments.

tod in the northeast and southeast embayments
measured, 87.5% (484 conch) were < 22.8 cm
:h) were >22.8 cm.

I in the northeast embayments of Cottongarden
in Figure 5. In Cottongarden Bay, mean conch
e measured conch were <22.8 cm. Mean conch
m); 89 % of the measured conch were <22.8 cm.
k (+/- SD = 4.24 cm); 88% of the measured






SEAMAP-C FY-2004 Supplemental 9
St Croix BackreefEmbayment Conch Assessment
Final Report
Length-frequency histograms for the conch found in the southeast embayments of Turner Hole
Bay, Robin Bay and Great Pond Bay are shown in Figure 6. Mean conch size in Turner Hole
Bay was 15.6 cm (+/- SD = 4.40 cm); 93 % of the conch were <22.8 cm. Mean conch size in
Robin Bay was 16.7 cm (+/- SD = 4.8 cm); 84% of the conch were <22.8 cm. Mean conch size
in Great Pond Bay was 17.5 cm (+/- SD = 5.28 cm); 78% of the conch were <22.8 cm.

The distribution of the five major habitat types within each embayment (seagrass, patch reef
algal plain, sand and rubble) is shown in Figure 7 (data from Mateo and Tobias 2001 and 2004).
In the northeast embayments of Cottongarden Bay, Teague Bay and YellowcliffBay, the
dominant habitat type was seagrass (94%, 84% and 61%, respectively). Algal plain was the
second most abundant habitat type in YellowcliffBay (26%) and Teague Bay (12%). The
dominant habitat type in the southeast embayments was seagrass in Turner Hole Bay and Robin
Bay (80% and 85%, respectively) followed by sand (12% and 9%/o, respectively). Great Pond
Bay habitat was dominated by sand (60%), seagrass (19%) and algal plain (19%).

The number of conch recorded by habitat type is shown in Figure 8 for the northeast
embayments and Figure 9 for the southeast embayments. Most (97.7%) conch observed were
recorded from three habitat types (sand-S, algal plain-AL and seagrass-SG) and five
combinations of these habitat types (S/AL, SG/S, S/SG, S/AL/SG and AL/SG). In northeast
embayments (Figure 8), 98% of conch observed in Cottongarden Bay were found in seagrass
(92%) and algal plain/seagrass habitat (6%). In Teague Bay, 91% of conch observed were
found in seagrass combination (62% algal plain/seagrass and sand/algal plain/seagrass) and
seagrass (29%) habitat. In YellowcliffBay, 83% of conch observed were found in seagrass
combination (60%-algal plain/seagrass) and seagrass (23%) habitat.

In the southeast embayments (Figure 9), 81% of conch observed in Turner Hole Bay were found
in seagrass combination (42% seagrass and 39%-sand/algal plain/seagrass and sand/seagrass)
habitats. In Robin Bay, 85% of conch observed were found in seagrass (53%) and seagrass
combination (32%-sand/seagrass and sand/ algal plain/seagrass) habitats. In Great Pond Bay,
43% of conch observed were found in seagrass and seagrass combination habitats, 33% were
found in sand/algal plain habitats and 15% were found in sand habitats.

The distribution of conch by size and habitat type for the northeast and southeast embayments is
shown in Figures 10 and 11, respectively. In Cottongarden Bay, 99% of conch < 22.8 cm were
found in seagrass and 100% of conch > 22.8 cm were found in seagrass (Figure 10). In Teague
Bay, 47% of conch < 22.8 cm were found in seagrass combination habitats and 24% in only
seagrass habitat. The majority of conch >22.8 cm were found in seagrass (42%) and sand/algal
plain (25%) habitats. In YellowcliffBay, conch < 22.8 cm were found in algal/seagrass (47%),
seagrass (24%) and sand/seagrass (14%) habitats. The majority of conch >22.8 cm were found
in sand/seagrass (50%) and seagrass (25%) habitats.

In the southeast embayments (Figure 11), in Turner Hole Bay, 43% of conch <22.8 cm were
found in seagrass, 25% in sand/algal plain/seagrass and 17% in sand/seagrass habitats. All conch
>22.8 cm in Turner Hole Bay were found in seagrass. In Robin Bay, 57% of conch < 22.8 cm
were found in seagrass, 21% in sand/seagrass and 18% in sand/algal plain/seagrass habitats.
Most of the conch >22.8 cm (60%) were found in seagrass. The majority of conch <22.8 cm in






SEAMAP-C FY-2004 Supplemental 10
St Croix Backreef Embayment Conch Assessment
Final Report
Great Pond Bay, were distributed between sand/algal plain, sand/seagrass and sand habitats
(31%, 28% and 16%, respectively). Conch >22.8 cm were found predominately in sand/algal
plain (38%) and sand (25%) habitats.


DISCUSSION

This study represents the first assessment of conch populations in the shallow (I to 7 m depth),
protected embayments of St. Croix, U.S. Virgin Islands. Conch densities in this study (43.8
conch/ha combined study area; 52.6 conch/ha and 33.6 conch/ha for the northeast and southeast
embayments, respectively) were found to be greater than those determined by previous
researchers for St. Croix of 7.6 conch/ha (Wood and Olsen 1983) and for St. Thomas/St. John of
9.70, 12.25 and 22.6 conch/ha (Woodi and Olsen 1983; Friedlander et al.. 1994; and Friedlander,
1997, respectively) on the insular shelf platform. In relation to adjacent Caribbean waters, St.
Croix backreef conch densities were greater than those reported by Torres-Rosado (1987) and
Mateo (1997) for Puerto Rico (8.1 and 7.4 to 9.2 conch/ha, respectively). However, adult conch
densities may not be sufficient to sustain inshore populations. According to Stoner and Ray
(1996), adult conch densities <53 conch/ha adversely affect the ability of conch to locate a mate
and reproduce. Therefore, conch densities in backreefembayments are extremely low for
reproduction.

A more recent Virgin Islands conch study by Gordon (2002), designed to resurvey sites visited in
1981 by Olsen and Wood (1983), reported total conch densities around St. Croix to be 99.7
conch/ha (72.3 juvenile conch/ha and 27.4 adult conch/ha) on the insular shelf platform. The
highest juvenile and adult densities were found in the 7 to 12 m depth and 19 to 24 m depth
range, respectively. These results are significantly higher than conch densities previously
determined by Olsen and Wood (1983) for St. Croix, as well as the results from this study.

Only four of the 16 sites surveyed by Gordon (2002) contained high numbers of conch,
indicating the patchy distribution of the resource. One of these sites was in Buck Island National
Monument waters, where harvest is now prohibited.

It is also possible that conch density recorded by Wood and Olsen (1983) was underestimated
due to the methodology they used. Wood and Olsen (1983) used a surface vessel following a
compass course to tow a diver in an underwater sled. The diver maintained the height of the sled
above the substrate with controls on the sled and counted the conch observed through a portion
of the sled frame. The opening through the sled frame at a specific height above the substrate
was predetermined to be a specified area of bottom habitat. However, since the sled was not
stopped when conch were observed, the numbers of conch could have easily been
underestimated. Conch with heavily colonized shells or shells partially buried in the substrate
could have been overlooked.

Differences in methodology make comparison of the present study to Gordon (2002) difficult.
Surveys by Gordon (2002) covered an average of 1,869 m2 of bottom habitat per survey. The
sites were surveyed once, comprising 2.99 ha of total habitat. The present study utilized more
extensive sampling in the six embayments, averaging 2.58 ha and 2.26 ha surveyed in each of the






SEAMAP-C FY-2004 Supplemental 11
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Final Report

northeast embayments and southeast embayments, respectively. The sites were also resurveyed
many times (monthly for a one-year period). Habitat differences are evident between the two
studies (Gordon 2002 and this study). The shelf areas surveyed by Gordon (2002) comprised
predominantly pavement (50%) and algal (27%) habitats. In the present study, seagrass was the
dominant habitat type (71%) in embayments. Both studies show the importance of vegetative
material as conch habitat. In Gordon (2002), the density ofjuveniles was greater in algae and the
density of adults was greater in seagrass. In the present study, the abundance of both juvenile
and adult conch were greater in seagrass habitats or combinations thereof.

Conch mature at 2.5 to 3 years of age and first reproduction occurs in years 3 to 4. By that time,
the shell lip has formed and thickened to 5 mm (Appeldoorn 1996). Stoner and Ray (1996)
reported that sexual maturity of conch begins at 20 cm shell length. The backreef embayments
studied on the northeast and southeast coast of St. Croix were found to contain predominately
juvenile conch. Length-frequency data show a mean conch size in all bays of 17.1 cm (SD =
1.21); 87% of the conch measured were <22.8 cm, the legal harvestable size. Stoner (1996)
determined that conch nursery areas are shallow seagrass meadows from <5 to 6 m in depth.
However, not all seagrass beds are nursery areas. Vast areas of seagrass meadows in Bahamas,
Belize, Mexico and Florida have only small areas suitable as nursery grounds because they lack
important recruitment and benthic habitat features (Stoner and Ray 1996). The most important
nursery habitats appear to be determined by complex interactions of physical oceanographic
features, seagrass and algal communities, and recruitment of larvae (Stoner 1996). The
abundance ofjuvenile conch in the backreefembayments observed in this study would indicate
that these embayments appear to have the requirements necessary to serve as nursery areas.

Five major habitat types were identified in the embayments, seagrass, patch reef, algal plain,
sand and rubble (Mateo and Tobias 2001 and 2004). Seagrass (T. testudimim and
T. testudinu/S. filiforme) was the dominant habitat type. A total of 98% of all conch observed
were recorded in sand, algal plain and seagrass habitats, or combinations thereof, which
comprised 96.3% of habitat surveyed. Of this total, 79% of all conch <22.8 cm and 63% of all
conch R22.8 cm were found in seagrass or seagrass combination habitats. Friedlander (1997)
found adult conch were most abundant in similar habitats around St. John.

Conch larvae remain part of the zooplankton community for 16 to 28 days (Stoner and Ray
1996). Prior to metamorphosis, conch larvae can be dispersed significant distances and also
become trapped in current eddies or gyres and retained or transported back to their natal
environs. The Teague Bay bank-barrier reef system on the northeast coast of St. Croix and the
bank-barrier/calcareous algal ridge system on the southeast coast form a nearly continuous
seaward barrier to the backreefembayments where conch studies were conducted (Burke et al.
1989; and Hubbard 1989). Although this reef feature reduces wind and wave energy to backreef
environs, water exchange remains excellent from a predominantly easterly regime of tradewinds
and seas (Burke et al. 1989; and Hubbard 1989). Current reversals (the flow of offshore water
from a westerly to easterly direction) have also been recorded (Hubbard 1989). Strong tidal
currents or a good flow of oceanic water are important criteria for a viable conch nursery area
(Stoner 1996). The bays on the north and south coast (with the exception of Turner Hole Bay)
are interconnected and longshore currents passing water over the reef or through natural
passageways continually exchange water. The longshore current flows in an east-west direction






SEAMAP-C FY-2004 Supplemental 12
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(W. Tobias, personal observation). Turner Hole Bay is separate to and located east of Robin and
Great Pond Bays on the southeast coast and has a deepwater passage through the reef at its
eastern end. The longshore current flows east to west but reverses west to east in the outer
embayment (W. Tobias, personal observation). Water flow is reduced to the west where the reef
system shoals to meet the western headland of Turner Hole Bay (W. Tobias, personal
observation). As an oceanic island (not immediately surrounded by other land masses), St. Croix
may receive recruitment of conch larvae from other nearby gene pools (Saba Bank to the east,
Anguilla and the British Virgin Islands to the north, Puerto Rico to the west), as well as assist in
replenishing its own conch population.

Conch have the ability to move up to 9 km in six months and the natural migration of conch is
from inshore waters to spawn in the summer months to deeper offshore waters in the winter
months (Appeldoor 1996). Although the bank-barrier reef system affords great protection to
backreef waters, the reef structure may also be a physical barrier to the movement and
inshore/offshore migration of conch. Most of the embayments studied here are less than 1 km in
length. Movement of adult and sub-conch in the embayments may be limited to an east-west
direction. Access offshore is restricted to natural passageways or channels through the reef.

The bank-barrier reef structure becomes less continuous west of the study sites. This barrier
effect could artificially enhance the numbers of adult conch found within the embayments, if
movement is restricted. This could facilitate user groups in locating and harvesting the conch
resource.

Historical accounts by St. Croix residents indicate that adult conch were so abundant in backreef
embayments that they could be located in shallow water without a diving mask by feeling them
with your feet (T. Skov, personal communication). At low tide, conch were exposed with their
shells above the water surface. With increased demand and the use of outboard engines instead
of sail power and the use of scuba gear instead of free diving, commercial fishers depleted adult
conch resources in shallow inshore waters and now harvest conch in deeper water near the shelf
edge (Rosario 1995; and CFMC 1996).

Presently, recreational and commercial fishing pressure may reduce both juvenile and adult
conch densities in the backreef embayments. Both juvenile and adult conch densities were
lowest in Cottongarden Bay on the northeast coast. On the southeast coast, Robin Bay and Great
Pond Bay juvenile densities were low and adult conch densities in all three southeast bays were
uniformly low. Beach camping on St. Croix is extremely popular, particularly during holiday
periods. Recreational harvesting of marine resources is problematic for enforcement in general
and at this time in particular. Beach camping activities occur in Cottongarden Bay at Cramer
Park, a public park, and at Robin Bay and Great Pond Bay, more isolated areas where beach
shacks have been constructed. Recreational fishers have been observed harvesting undersized
conch in Teague Bay and conch shell middens occur on the shoreline in Yellowcliff, Robin and
Great Pond Bays (W. Tobias, personal observation). Juvenile conch densities may be lower in
Robin Bay and Great Pond Bay because these bays are more isolated and harvesting of juveniles
can persist without observation from enforcement. In the absence of fishing, the backreef
embayments would have more adult conch for stock replenishment.






SEAMAP-C FY-2004 Supplemental
St. Croix Backreef Embayment Conch Ass


CONCLUSION

The backreef embayments studied appear to be
However, adult conch density observed is insult
population. Shoreline conch middens show thE
juvenile and adults are removed (CFMC 1999)
Islands in 1994 (VIRR 1994; and CFMC 2001'
shelf waters, enforcement of the regulations is
isolated areas of the coastline. Increased enfor
facilities, and better monitoring of conch harve
of present management regulations. A public a
educate the public on the importance ofmanag
regulations.

There are over 2,000 registered boats in the U.
and it is estimated that approximately 10% oft
activities (Jennings 1992; and Mateo 1999). B
number of recreational fishers, how many of th
of this harvest on conch resources. A recreatic
from licensed fishers should be instituted to en;
fishing effort on the resource. Random shoreli
accuracy of data submitted by recreational fish

Fishing is not the only adverse impact on condc
has been lost in the Virgin Islands due to habit;
quality degradation from non-point source and
coastal waters and important essential fish habi
Islands should adopt uniform development reg

Cottongarden Bay, Teague Bay, YelloweliffB;
Bay lie within the St. Croix East End Marine P
established in 2002 (The Nature Conservancy :
EEMP's 27 km of shoreline. The waters ofthi
identified as designated use zones. With the pi
and the hiring of dedicated enforcement officer
protection can be afforded to the essential fish
backreef embayments.

With the restriction of fishing effort anticipated
from shelf waters in backreef embayments may
larvae. The adult conch may serve as a valuab]
replenish an inshore conch population.


13





nportant nursery ground for juvenile conch.
cient to support a once abundant inshore conch
the harvest of conch is opportunistic and both
While regulations established in the U. S. Virgin
appear adequate to sustain conch harvests from
united at best and may be lacking in more
:ment presence, particularly at boat access
ing is necessary to determine the effectiveness
,areness program should be established to
g conch resources and current rules and


. Virgin Islands (Eastern Caribbean Center 2002)
Population participate in recreational fishing
ever, no information is available on the exact
n are harvesting conch and the potential impact
al license system with mandatory data collection
le fisheries managers to determine landings and
surveys should be conducted to determine the
s.

resources. Important coastal fisheries habitat
destruction from coastal development and water
oint source pollution. To enhance protection to
.ts found therein, the Government of the Virgin
itions for shoreline and inland areas.

, Turner Hole Bay, Robin Bay and Great Pond
*k (EEMP), a 155 km territorial marine park
02). These embayments comprise part of the
e embayments and those offshore have been
mulgation of rules and regulations for the EEMP
and interpreters, it is anticipated that greater
ibitat and marine resources found in these


a the EEMP, the introduction of adult conch
elp to supplement the inshore supply of conch
source of conch propagules to once again






SEAMAP-C FY-2004 Supplemental 14
St. Croix BackreefEmbayment Conch Assessment
Final Report

Future conch studies should be conducted to obtain specific information relevant to stock
assessment. These studies in the backreefembayments should include information on the
following:

1. recruitment of conch larvae;
2. currents/hydrodynamics within bays;
3. habitat for juvenile conch <7.0 cm;
4. habitat where conch are found during census;
5. conch lip measurements;
6. conch tagging studies to identify movement;
7. estimates of recreational conch harvest; and
8. seasonal abundance and distribution of egg masses.


ACKNOWLEDGMENTS

Ivan Mateo assisted in the collection of conch data and statistical interpretation of the results.
Christine O'Sullivan formatted the figures for the report. Jennifer Valiulis entered date into a
database.


LITERATURE CITED

Appeldoornm, R.S. 1996. Status of the queen conch fishery in the Caribbean Sea. pp.40-59 In:
J.M. Posada and G. Garcia-Moliner (eds). 1997. Proc. of the International Queen Conch
Conference, San Juan, Puerto Rico, July 29-31, 1996. CFMC, San Juan, Puerto Rico. 155
PP-

Appeldoorn, R.S. and B. Rodriguez (eds). 1994. Queen conch Biology, Fisheries and
Mariculture. Fundacion Cientifica Los Roques, Caracas, Venezuela. 356 pp.

Bruce, G., J. Harkness, J. Hewlett, M. Hill, D. Hubbard, T. McGovern, C. Reed and H. Roberts.
1989. Sedimentary environments of Great Pond Bay, St. Croix, U.S. Virgin Islands.
pp.161-166. In: D. Hubbard (ed). 1989. Terrestrial and marine geology of St. Croix..
213 pp.

Burke, R.B., W.H. Adey, and I.G. MacIntyre. 1989. Overview of the Holocene history,
architecture and structural components of Teague Reef and Lagoon. pp. 111-117. In: D.
Hubbard (ed). 1989. Terrestrial and marine geology of St. Croix. 213 pp.

CFMC. 1996. Fishery Management Plan Regulatory Impact Review, and Final Environmental
Impact Statement for the Queen Conch Resources of Puerto Rico and the United States
Virgin Islands. Caribbean Fishery Management Council, NMFS. June, 1996.

CFMC. 1999. Queen conch stock assessment and management workshop. 105 pp.






SEAMAP-C FY-2004 Supplemental 15
St. Croix BackreefEmbayment Conch Assessment
Final Report

CFMC. 2001. Draft amendment 2 to the Fishery Management Plan, queen conch resources of
Puerto Rico and the United States Virgin Islands-including a regulatory impact review and
initial regulatory review and draft supplemental environmental impact statement.

Chakalall, B. and K. L. Cochrane. 1996. The queen conch fishery in the Caribbean an
approach to responsible fisheries management. pp.60-76 In: J.M. Posada and G. Garcia-
Moliner (eds). 1997. Proc. of the International Queen Conch Conference, San Juan, Puerto
Rico, July 29-31, 1996. CFMC, San Juan, Puerto Rico. 155 pp.


Clavijo, I.E., W. Tobias and C. Jennings. 1986. State/Federal Cooperative Statistics Program
Completion Report-Virgin Islands (April 1, 1983-March 31, 1986). 29 pp.

Dammann, S.E. 1969. Study of the fisheries potential of the Virgin Islands. Contrib. No.1
VIERS. 167 pp.

Eastern Caribbean Center. 2002. Telephone survey of boat-based marine recreational fishing in
the U.S. Virgin Islands, 2000. 51 pp.

Friedlander, A.M. 1997. Status of the queen conch populations around the northern USVI with
management recommendations for the Virgin Islands National Park. Report prepared for
USGS, St. John, USVI. 40 pp.

Friedlander, A.M., Appeldoorn, R.S. and J. Beets. 1994. Spatial and temporal variations in
stock abundance of queen conch, Strombus gigas, in the U.S. Virgin Islands. pp.51-60. In:
Appeldoorn, RS., B; Rodriquez (eds), 1994. Queen Conch Biology, Fisheries and
Mariculture. Fundcion Cientifica Los Roques, Caracas, Venezuela, 359 pp.

Garcia-Moliner, G. 1997. Status of the fisheries regulations regarding queen conch, Strombus
gigas, in the United States, including Florida, the Commonwealth of Puerto Rico and the
territory of the Virgin Islands. pp.124-135. In: J.M. Posada and G. Garcia-Moliner (eds).
1997. Proc. of the International Queen Conch Conference, San Juan, Puerto Rico, July 29-
31, 1996. CFMC, San Juan, Puerto Rico 155 pp.

Garcia-Moliner, G., W. R. Keithly, Jr. and I.N. Olivaras. 1999 Recreational scuba diving
activity in the U.S. Caribbean. Gulf& Carib. Fish. Inst. 52:363-371.

Gordon, S. 2002. United States queen conch assessment. Proceedings 57th Ann. Gulf& Carib.
Fish Inst. In press.

Hubbard, D. 1989. Depositional environments of Turner Hole reef complex. pp.155-161. In:
Hubbard, d (ed). Terrestrial and marine geology of St. Croix, U.S. Virgin Islands. Special
Pub. No.8, West Indies Lab., Teague Bay, St. Croix. 213 pp.

Jennings, C.A. 1992. Survey ofnon-charter boat recreational fishing in the U.S. Virgin Islands.
Bull. Mar. Sci. 50(2): 342-351.






SEAMAP-C FY-2004 Supplemental 16
St Croix Backreef Embayment Conch Assessment
Final Report


Kendall, M.S., M.E. Monaco, K.R. Buja, J.D. Christensen, C.R. Kruer, M. Finkbeiner and RA.
Warner. 2001. Methods used to map the benthic habitats of Puerto Rico and the U.S.
Virgin Islands. URL: http://biogeo.nos.noaa.gov/projects/mapping/caribbean/startup.htm.

Kojis, B. 2004. Census of the marine commercial fishers of the U.S. Virgin Islands. CFMC
rept. 86 pp.

Mateo, 1. 1997. Spatial variations in stock abundance of queen conch Strombus gigas in the
west and east coasts of Puerto Rico. MS thesis, University of Puerto Rico, Mayaguez,
Puerto Rico.

Mateo, I. 1999. Annual report recreational fishery assessment project F-8-9 Job 7: Angler
telephone household survey. Division of Fish and Wildlife. 10 pp.

Mateo, I. and W. Tobias. 2001. Distribution of shallow water coral reef fishes on the northeast
coast of St. Croix, USVI. -Carib. J. Sci. 37:210-226.

Mateo, I. and W. Tobias. 2004. Survey ofnearshore fish communities on tropical backreef
lagoons on the southeastern cost of St. Croix. Carib. J. Sci. 40:327-342.

Randall, J.E. 1964. Contributions to the biology of the queen conch, Strombusgigas. Bull.
Mar. Sci. GulfCaribb. 14:247-295.

Rivera, J. 1999. Queen conch cpue assessment in Puerto Rico and the U.S. Virgin Islands:
preliminary report to CFMC. 18 pp.

Rosario, I. 1995. Queen conch stratification survey. SEAMAP-C report to CFMC.
34 pp.

Stoner, A.W. 1996. Status of queen conch research in the Caribbean. pp.23-39. In: Posada,
J.M. and G. Garcia-Moliner (eds). 1997. Proc. of the International Queen Conch
Conference, San Juan, Puerto Rico, July 29-31, 1996. CFMC, San Juan, Puerto Rico
155 pp.

Stoner, AW. and M. Ray. 1996. Queen conch, Strombusgigas, in fished and unfished locations
of the Bahamas: effects of a marine fishery reserve on adults, juveniles and larval
production. Fish. Bull. 94:551-565.

The Nature Conservancy. 2002. St. Croix East End Marine Park management plan. 111 pp.

Tobias, W. 1987. Biostatistical data on commercially harvested queen conch, Strombus gigas,
from the insular shelf around St. Croix, U.S. Virgin Islands. CFMC Tech. Rept. 20 pp.

Tobias, W., R. Gomez and B. Kojis. 2000. Three-year summary report, 1 April 1997-






SEAMAP-C FY-2004 Supplemental 17
St Croix BackreefEmbayment Conch Assessment
Final Report

31 March 1999, Cooperative Statistics Program, NA77FT0093. NMFS Cooperative
Statatistics Program Rept. 10 pp.

Torres-Rosado, Z.A. 1987. Distribution of two mesogastropods, the queen conch, Strombus
gigas Linnaeus, and the milk conch, Strombus costatus Gmelin, in La Paguera, Lajas,
Puerto Rico. MS thesis, University of Puerto Rico, Mayaguez, Puerto Rico. 37 pp.

Valle-Esquivel, M. 2002a. U.S. Caribbean queen conch data update with emphasis on the
commercial landings statistics. NOAA/NMFS/SEFSC Miami Laboratory SFD-01/02-169.
118 pp.

Valle-Esquivel, M. 2002b. Standardized catch rates and preliminary assessment scenarios for
queen conch (Strombus gigas) in the U.S. Caribbean. NOAA/NMFS/SEFSC Miami
Laboratory SFD-02/03-184. 63 pp.

Virgin Islands Rules and Regulations (VIRR). 1994. Amended rules and regulations "conch and
whelk harvesting" for the United States Virgin Islands, Subchapters 301-307, 316 and 325.
Title 12, Chapter 9A. Rules and Regulations Commercial Fishing.

Wood, R.S. and D.O. Olsen. 1983. Application of biological knowledge to the management of
the Virgin Islands conch fishery. Proc. Gulf& Carib. Fish. Inst. 35:112-121.

Zar, J.H. 1984. Biostatistical Analysis 2nd ed. Prientice Hall, New Jersey. 718 pp.






SEAMAP-C FY-2004 Supplemental 18
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"TB











RB

-GPB sSt. Croaix





Figure 1: Location and site map of the back reef embayments sampled for conch on the northeast and southeast coasts of St. Croix,
US Virgin Islands. CB Cottongarden Bay, TB Teague Bay, YB YellowcliffBay, THB Turner Hole Bay, RB Robin Bay,
GPB Great Pond Bay.







SEAMAP-C FY-2004 Supplemental
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Total Conch Density

0 Recorded Conch


80




d








ce ra Ye Re i



Figure 2: Total conch density for the back reef embayments. CB Cottongarden Bay, TB -
Teague Bay, YB Yellowcliff Bay, TIB Turner Hole Bay, RB Robin Bay, GPB Great
Pond Bay.


Conch Density by Size Categories
so

70 1>22.8an

80



40
30
d
10

20



Co-- -B YB TH RB .
CS TB YB TH RB GP


Figure 3: Conch density by size category for the back reefemrbayments. CB Cottongarden Bay,
TB Teague Bay, YB YellowcliffBay, THB Turner Hole Bay, RB Robin Bay, GPB -
Great Pond Bay.






SEAMAP-C FY-2004 Supplemental 20
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Total Conch All Bays


50


40-

30-
S-
O




20



10


0-
20-


IAlf 11 1 1 J J11'r I 1 '.. t r11VI


<1 T Ito
r r r
N (4 4 1
r r r r


M^Q4^pz l3- cy%/g re ueeL
i/ = 553 conch


minimum harvest size = 22,8 cm




Hnnfnn


F] _,


o N Ce) Mr to (a G- o Go
C N MN N N N 2 N N N
a) 0 M ;4 4r
T- N N N


Shell Length (cm)

Figure 4: Length-frequency distribution for all conch found in the northeast and southeast embayments of St. Croix, U.S. Virgin
Islands, in September 1998-October 1999 and July 2000-September 2001.


ttO1I


.. E .


' ' ' ' "


I `


-


v C
Cb








SEAMAP-C FY-2004 Supplemental
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Final Report





20
Cotton

18-
16 -

14

12

10


9s


4-

2 -

20

1a- Tea





c 12-

10-





4

2 -
'20 n- "


eS1 YelloN






10




8

4-
1c *








2 -
10 -



6.








She

Figure 5: Length-frequency data for conch foL


21







SEAMAP-C FY-2004 Supplemental
St Croix BackreefEmbayment Conch Assessment
Final Report


Turner Hole


Robin Bay


n'zl44conch


n = 144 conch
251 transects






minimum hardest size= 22,8 cm
f 1


n n


H n n n n


n = 38 conch
200 transacts


minimum harvest size 22.B cm








Great Pond Bay


n = 48 conch
219 transects


minimum harvest size= 22.5 cm






nnnnnnn~nnnnnnp


Figure 6: Length-frequency data for conch found in the southeastern embayments.


nih


2-





.0-

16B

14-
8-
120
108


6
4
2


G O Nr A V M V 6 40 r E M c r M LO t oA
SChl C4 CN 4 4 emN
Shell Length 4cm)


7~"-~~-TI*~7-~L-C~-L-+l`-`--f~--


_I


0 4-


--------------






SEAMAP-C FY-2004 Supplemental
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Habitat Distribution


CB TB YB TH RB GP
Site


I IOSeagrass OIPatch Reef EAlgal Plain USand BRubble I
Figure 7: Percent cover of habitat in the back reef embayment study sites (from Mateo and Tobias 2001, 2004).
CB Cottongarden Bay, TB Teague Bay, YB YellowcliffBay, THB Turner Hole Bay, RB Robin Bay, GPB Great Pond
Bay.







SEAMAP-C FY-2004 Supplemental
St. Croix Backreef Embayment Conch Assessment
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no. transects 28
no. conch = 105


go no. itnaect 241
n 10 conch


go] no. Irans*ct 201
n= 131 conch


Cottongarden Bay Habitat


Teague Bay Habitat


Yellowcliff Bay Habitat


S ASL S/AL SG/S S/SG S/AUSG ALSG SO
Habitat Typ*
Figure 8: Number of conch by habitat type in the northeastern embayments. S = Sand, AL =
Algal plain, S/AL = Sand / Algal Plain, SG/S = Seagrass / Sand, S/SG = Sand / Seagrass,
S/AL/SG = Sand / Algal Plain / Seagrass, AL / SG = Algal Plain / Seagrass, SG = Seagrass.








SEAMAP-C FY-2004 Supplemental 25
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,00.------------------------------
na. rans..cr-25 Turner Hole Bay Habitat
o9 n 144 cnch

eo -

70



50-

40






I03 I I,

no. tran.t.o= 0o Robin Bay Habitat

BD









20-
0 -
=219







sa n--4"canch Great Pond Bay Habitat



n -
60




40 *





to
t 0 .......... ... I 1 I- -- I
S AL S/AL SG/S S/SO S/AL/SG ALSG SG
Habtat Type

Figure 9: Number of conch by habitat type in the southeastern embayments. S = Sand, AL =
Algal plain, S/AL = Sand / Algal Plain, SG/S = Seagrass / Sand, S/SG = Sand / Seagrass,
S/AL/SG = Sand / Algal Plain / Seagrass, AL / SG = Algal Plain / Seagrass, SG = Seagrass.
Fiue9 ubro oc yhbtttp n h otesenebyet.S=SnA

Ala liSA ad/Aga liS/ egas/Sad /G=Sn egas






SEAMAP-C FY-2004 Supplemental
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Final Report.
10 Cottongarden Bay Conch Size
90 m Canch<22.8 cm (n 75)
WO Conch>22.B cm (n = )


Teague Bay Conch Size


- r---L. ] l
a conch<22.a cm(n= ail) Yellowcllff Bay Conch Size
f Conch>22.S cm (n = l2)


FL.FL


S ,l L ........ .. [ ...... I .6 I
S AL S/AL SGS S/SG S/AL/SG ALSG SO
Habitat Type
Figure 10: Number of conch by size and habitat type in the northeast embayments. S = Sand,
AL = Algal plain, S/AL = Sand / Algal Plain, SG/S = Seagrass / Sand, S/SG = Sand /
Seagrass, S/AL/SG = Sand / Algal Plain / Seagrass, AL / SG = Algal Plain / Seagrass, SG =
Seagrass.


oConch<22.8 cm fn= 10o7)
mConch>22. crm (n=: 12)







SEAMAP-C FY-2004 Supplemental
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J hcscoc<2za m (n 12) Turner Hole Bay Conch Size
M Conch>22.B cm (n 4)
s0


I_-ri_. -_ _.-.-__


Doneah=2.aocm(n r 28) Robin Bay Conch Size
I Conch>22.B cm (n 5)














. .. ........ .. . .. ................. .... .. .... .. . .. .... . .. ... ....
Ccnnch>22.e m(n=32) Great Pond Bay Conch Size
lCanch>22.B cm (n 8)


m"-1


'I


AL S/AL


S01S S/SG
Habitat Type


S/ALSO ALUaSG


Figure 11: Number of conch by size and habitat type in the southeast embayments. S = Sand, AL
= Algal plain, S/AL = Sand / Algal Plain, SG/S = Seagrass / Sand, S/SG = Sand / Seagrass,
S/AL/SG = Sand / Algal Plain / Seagrass, AL / SG = Algal Plain / Seagrass, SG = Seagrass.


IF


__._ _rLI-III_I~IILII_


| i II _ -






SEAMAP-C FY-2004 Supplemental 28
St. Croix BackreefEmbayment Conch Assessment
Final Report

Table 1. Total number of conch observed and total conch density in the three northeast and
three southeast embayments of St. Croix, U.S. Virgin Islands, September 1998-October 1999
and July 2000-September 2001, respectively._
Northeast Southeast Combined Study Area
Embayments Embayments (Northeast + Southeast
Embayments)
Total Number of Conch 408 228 636

Total Area Surveyed (ha) 7.75 6.78 14.53

Total Density (total conch/ha) 52.6 33.6 43.8









ia






SEAMAP-C FY-2004 Supplemental
St. Croix Backreef Embayment Conch Assessment
Final Report


Table 2. Summary of conch number and density in the three northeast and three southeast embayments
Virgin Islands from data collected in September 1998-October 1999 and July 2000-September 2001, re
Number Number of Conch** Dens
of Area Surveyed
Site Transects* (m2 ha) Total <22.8 cm >22.8 cm Total
Northeast Embayments -
Total 775 77,500- 7.78 408
Average/embayment 258.3 25,833 2.58 136 94.0 14.3 52.6

Southeast Embayments
Total 678 67,800 6.78 228
Average/embayment 226.0 22,600 2.26 76 67.3 8.7 33.6
* Transects = 50 m x 2 m = 100 m.
** The total number of conch represents the total conch recorded. All measured conch were placed
22.8 cm which represents the minimum harvest size. A total of 83 conch from the northeast embi
the nearest millimeter but placed in size categories (18 conch <100 mm, 42 conch = 100-200 mm
Therefore, the calculations of the average number and density of conch <22.8 cm and > 22.8 cm f
may be approximately 10-20% low.
*** Total conch density was determined from the total number of conch recorded.






SEAMAP-C FY-2004 Supplemental
St Croix Backreef Embayment Conch Assessment
Final Report


Table 3. Number of conch observed in the northeast and southeast embayments of St. Croix, U.S. Virgin Islands, September 1998-
October 1999 and Jul 2000-September 2001, respectively.
Number Total Transect Depth No. Range of
of Area Surveyed Conch Depth (m) Range Conch/Transect Individuals/
Site Transects* (m2 ha) Observed (Mean +/- SD) (m) (Mean +/- SD) Transect
Northeast Embayments
CottongardenBay 278 27,800- 2.78 105 3.0(0.84) 1.2-5.5 0.37 (0.917) 0-6
Teague Bay 260 26,000 2.60 170 4.5 (1.65) 1.2 6.7 0.65 (1.893) 0-20
YelloweliffBay 237 23,700 2.37 133 4.8 (1.54) 0.9 7.3 0.56 (1.629) 0-17
subtotal 775 408
Southeast Embayments
Turner Hole 251 25,100 2.51 144 2.9(1.01) 0.9 7.0 0.57 (2.144) 0 29
Robin Bay 208 20,800- 2.08 38 1.9(0.89) 0.6-6.7 0.18 (0.569) 0-5
Great Pond Bay 219 21,900 2.19 46 2.6 (0.72) 0.9 5.1 0.21 (0.508) 0-3
subtotal 678 228
Total: 1,453 636


* Transects = 50 m x 2 m = 100 m2






SEAMAP-C FY-2004 Supplemental
St. Croix Backreef Embayment Conch Assessment
Final Report


Table 4. Density of conch calculated in the northeast and southeast embayments on St. Croix, U.S. Virgin Islands from data
collected in September 1998-October 1999 and July 2000-September 2001, respectively.
Number of Area Surveyed Number of Conch** Density (conch/ha)***
Site Transects* (m2 ha) Total <22.8 cm >22.8 cm Total <22.8 cm >22.8 cm
Northeast Embayments ______________
CottongardenBay -278 27,800 -2.78 105 75 6 37.76 28.40 2.27
TeagueBay 260 26,000- 2.60 170 115 14 65.38 44.23 5.38
YellowcliffBay 237 23,700- 2.37 133 92 23 56.11 38.81 9.70
subtotal: 775 408
SoutheastEmbayments
Turner Hole 251 25,100 2.51 144 134 10 57.37 53.38 3.98
Robin Bay 208 20,800-2.08 38 32 6 18.27 15.38 2.88
Great Pond Bay 219 21,900 2.19 46 36 10 21.00 16.43 4.56
subtotal: 678 228
Total: 1,453 636_______________
* Transects = 50 m x 2 m = 100 m.
** The total number of conch represents the total conch recorded. All measured conch were placed in size categories of< or > 22.8
cm which represents the minimum harvest size. A total of 83 conch from the northeast embayments were not measured to the
nearest millimeter but placed in size categories (18 conch <100 mm, 42 conch = 100-200 mm and 23 conch >200 mm).
Therefore, the calculations of the average number and density of conch <22.8 cm and > 22.8 cm from the northeast embayments
may be approximately 10-20% low.
*** Total conch density was determined from the total number of conch recorded.




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