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Title: A population survey of the West Indian topshell of whelk (Cittarium pica) in the U.S. Virgin Islands
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Title: A population survey of the West Indian topshell of whelk (Cittarium pica) in the U.S. Virgin Islands
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Language: English
Creator: Toller, Wes
Publisher: Division of Fish & Wildlife, Department of Planning and Natural Resources, Government of the U.S. Virgin Islands
Place of Publication: St. Croix, USVI
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Bibliographic ID: CA01300926
Volume ID: VID00001
Source Institution: University of the Virgin Islands
Holding Location: University of Florida
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A POPULATION SURVEY OF THE WEST INDIAN
TOPSHELL OR WHELK (CITTARIUM PICA)
IN THE U.S. VIRGIN ISLANDS






Wes Toller, Ph.D.

and

Shenell Gordon


Bureau of Fisheries
Division of Fish and Wildlife
Department of Planning and Natural Resources
Government of the U.S. Virgin Islands


January, 2005






SEAMAP-C: USVI Whelk Survey Final Report


Abstract

Populations of the West Indian topshell, Cittarium pica (Gastropoda: Trochidae), were surveyed
at 41 areas in the U.S. Virgin Islands between June 2003 and May 2004. The size and density of
C. pica, known locally as whelk, varied substantially among sites, but was not significantly
different between northern islands (St. Thomas, St. John, associated cays) and the southern
island (St. Croix). Average size was significantly different between island groups and showed a
non-significant negative relation to density. Observed spatial variability was partly explained by
habitat exposure: whelk at windward sites (offshore cays, exposed points) had larger average size
and occurred at lower density, whelk at leeward sites (bays, semi-protected coasts) had smaller
average size but occurred at higher density. Larger adult C. pica were rare or absent at most sites
although their densities were comparatively high within two marine protected areas, a restricted-
entry area, and at a number of sites characterized by exposure to high wave energy. Comparison
to limited historic USVI data for C. pica suggests a decline in the relative abundance of large
individuals. Together, these observations suggest that harvesting is a major influence upon, if not
the primary determinant of, C. pica population structure in the USVI. Data from paired-sampling
(leeward and windward sides) indicate that whelk young-of-the-year (YOY) are more abundant
on leeward coasts, which suggests that local patterns of whelk recruitment may be influenced by
nearshore oceanographic processes. A peak in YOY density was observed in spring and the
significance of this observation is discussed in relation to periods of annual spawning.
Recommendations for additional studies are presented.


Introduction

The West Indian topshell, Cittarium pica, is a trochid gastropod that inhabits rocky shorelines
which are exposed to wave action (Randall 1964). It is commonly found in the intertidal and
shallow subtidal areas the yellow and pink zones (Lewis 1960, Kaplan 1988) where it grazes
on a variety of predominantly filamentous forms of algae (Randall 1964). C. pica is distributed
throughout the Caribbean and Bahamas, with comparatively recent extinctions reported from
Bermuda and Florida (Abbott 1976). It attains a relatively large size of about 10 to 12 cm and
Fisher (1978) reports a maximum length of 13.6 cm. Owing to its edible qualities (Clench and
Abbott 1943), C. pica is commonly harvested for food throughout much of its range (Fisher
1978). Near human population centers, larger individuals are rare (Clench and Abbott 1943) and
overexploitation has become a concern throughout much of its range (Carter 2002).

In the United States Virgin Islands (USVI), West Indian topshells are also a popular food item,
known locally as whelks (Randall 1964), and humans have harvested whelks from local
shorelines since pre-Columbian times (R. Boulon pers. comm.). Presently, whelks are also
harvested commercially in the USVI and whole animals (in the shell) are sold for about US$10
per pound (Holt and Uwate 2004, R. Gomez pers. comm.). Although commercial, recreational,
and subsistence harvesting occurs in the USVI (Clavijo et al. 1984), little is known of the fishery
and less still is known about the impact of harvesting upon C. pica populations. In the late
1980's, concerns over declining whelk stocks (deGraaf and Moore 1987) prompted Territorial






SEAMAP-C: USVI Whelk Survey Final Report


regulations on whelk harvest, including a minimum harvest size and a 6-month closed season.
However, the efficacy of these policies to protect and restore C. pica stocks was never evaluated.

This study was undertaken to collect baseline information on C. pica populations in the USVI.
Our objectives were to quantify the abundance and size structure of C. pica across a large spatial
scale, to compare populations between island groups, to evaluate results in light of existing
information, and to identify significant data needs. The expansive spatial scale of sampling
necessarily led us to quite different locales within the USVI. It became apparent during our
surveys that some of the variability in C. pica population structure was related to differences in
physical attributes among habitats. Therefore, an attempt was made to incorporate observations
on habitat into the findings of this study.


Materials and Methods

Study Location

This study was conducted in the U.S. Virgin Islands (USVI). The northern USVI are composed
of two large islands St. Thomas and St. John and numerous smaller associated islands or cays
(Dammann and Nellis 1992) which arise from the Puerto Rico-Virgin Islands Platform (Nagle
and Hubbard 1989). St. Croix lies on a separate platform situated about 40 miles to the south. St.
Croix is separated from the northern USVI by a deep oceanic trench and it has four associated
cays. Collectively the USVI has about 380 km of shoreline distributed roughly as follows: St.
Croix with 113 km, St. Thomas with 85 km, St. John with 80 km, and the outlying cays and
islands with another 98 km (Dammann and Nellis 1992). Only about 80 km of shoreline is sand
beach located in bays and between headlands. The linear amount of shoreline which is
potentially available as whelk habitat (i.e. intertidal hard substrate) is unknown. Tidal exchange
is generally small (< 20 cm) in the USVI and of mixed semi-diurnal nature (Hubbard 1989).

Fisher Interviews and Site Selection

In an attempt to focus our sampling efforts to suitable whelk habitat, and to minimize sampling
from inappropriate habitats, DFW staff sought advisement from USVI commercial fishers.
Between March and July of 2003, a query was made of those fishers who harvest whelk, as
identified through a review of reported commercial landings from 1998 to 2003 (commercial
catch report database maintained by DFW). An announcement describing the study was also
prepared and distributed. Each fisher was asked to identify substantial whelk populations by
marking areas on a map. There were 10, 18 and 3 respondents on St. Croix, St. Thomas, and St.
John, respectively. Typically, fishers identified large stretches of rocky coastline, headlands, or
offshore cays (Table 1). These responses guided the selection of specific survey sites. Additional
sites were included for comparison to historic data (see below) and/or to increase the geographic
coverage of the study.






SEAMAP-C: USVI Whelk Survey Final Report


Body Size Measurement

Whelk body size has been reported in terms of shell length (Randall 1964), shell height (Debrot
1990a), and shell width (Schmidt et al. 2002). To standardize our data collection in a manner
most useful for management, we used a measure of shell width: the maximum diameter obtained
as measured with calipers across the base of the shell (Debrot 1987). Because minimum harvest
size for whelk in the USVI is 2-7/16ths inches (61.92 mm) or 62 mm shell size (I. Mateo cited in
Schmidt et al. 2002), we used a value of 62 mm shell width to delineate harvest-size whelks in
our samples. However a more accurate interpretation is noted here. USVI regulations specify
minimum whelk harvest-size as the inability of a shell to pass through a measuring loop of
nominal diameter 2-7/16ths inches (see USVI Code 1994). This differs substantively from a linear
measure of maximum shell width. For example, a whelk of 62.5 mm shell width will not pass
through such a loop when oriented with the shell base parallel to the plane of the loop but, due to
its 3-dimensional nature (conical, irregular), the same shell will easily pass through the loop if
oriented at an angle (J. Aubain pers. comm.). Strict adherence to the latter definition would
specify whelk of a substantially larger minimum size (perhaps as large as 65-70 mm shell width).
Exactly how to measure the legal harvest-size of whelks should be clarified for the public and
resource managers alike.

Evaluation of Field Sampling Protocols

Previous researchers have used a number of different survey methods to study C. pica
populations (e.g. Randall 1964, Clavijo et al. 1984, Boulon 1987, Debrot 1987, 1990a, 1990b,
Bell 1992). We sought a quantitative survey method that was applicable across a wide variety of
habitats. Two protocols were evaluated here: a quadrat method (Debrot 1990b modified from
Hughes 1971) and a cross-shore "strip transect" method (Boulon 1987). The quadrat method is
described below. Boulon's (1987) cross-shore transects are linear swaths (1.0 m wide) oriented
perpendicular to the shoreline. Their length is not pre-defined. Instead, cross-shore transects
begin at the highest intertidal zone and extend to a specified depth (1 m) in the shallow subtidal
zone. Cross-shore transects are advantageous because in each replicate whelk are sampled from
all intertidal zones. Their primary disadvantage is that the length of each cross-shore transect will
be determined by shoreline topography (i.e. by the width of the rocky intertidal zone itself).
Width of the intertidal zone may vary considerably within and among sites in the USVI
depending upon slope and substrate composition (Toller pers. obs.).

In May-June of 2003, preliminary surveys were conducted at Sprat Hall (SPH), St. Croix, using
both methods. SPH site lies on the western shore (leeward shore) where wave action is usually
moderate during summer months, making it amenable to studies. At SPH, whelks inhabit a short
(-150 m in length) contiguous stretch of rocky coastline. Results from the cross-shore transect
method and the quadrat method are shown in Table 2. The two methods yielded
indistinguishable size frequency distributions for C. pica (not shown). Estimates of abundance
from cross-shore transects were approximately twice those estimates derived from quadrats but
quadrat estimates had lower variance. When scaled to total habitat area, the two estimates
showed good agreement (Table 2). Given an overall similarity of results obtained from these
methods, the quadrat method was selected because: 1) density was considered a preferable unit






SEAMAP-C: USVI Whelk Survey Final Report


of measure for comparisons among sites, and 2) the quadrat method was more practical for
sampling from a diversity of habitats, often under challenging sea conditions.

Field Sampling Methods

The quadrat method was as follows. A 100 m transect tape or a 100-m rope (marked at 1 m
intervals) served as a reference line running parallel to shore. It was affixed in the littoral zone
and was stretched haphazardly through suitable C. pica habitat the yellow-to-pink zones of
intertidal substrate (Lewis 1960, Kaplan 1988). The reference line was secured to intermediate
tie-down points to resist wave action, usually resulting in a zigzag pattern that traversed
emergent and submerged littoral zones multiple times within each site. At pre-selected random
distances, a 1.0 m2 PVC quadrat was placed over appropriate C. pica habitat. All whelks found
within the quadrat frame were collected and shell width was measured to the nearest mm using
calipers. The area within each quadrat was searched visually (with the aid of a mask for subtidal
portions) and by probing crevices and running hands through macroalgae until no more whelks
were encountered. Between 8 and 17 replicate quadrats were done per survey site depending
upon C. pica abundance and prevailing sea conditions.

From initial observations (at SPH and elsewhere) and previous reports (e.g. Boulon 1987), it was
anticipated that harvest-size C. pica (> 62 mm shell width) would occur in very low densities at
some USVI sites. To adequately sample this rare, but economically important, part of the
population, a belt transect method was employed. Duplicate belt transects (50 m2) were
conducted parallel to the shoreline. Two divers surveyed 0.5 m on either side of a reference line
(a 1.0 m-wide swath) for 50 m, collecting all individuals estimated at > 62 mm shell width.
Shells were measured (as above) and whelks were returned to their site of capture. The belt
transect method was included to sample from a larger area than would be possible using 1.0 m2
quadrats its use serves a different purpose than the cross-shore transect method of Boulon (1987)
that was discussed previously (see above).

Placement of the reference line was the same for quadrats and belt transects. In principle, this
could result in double sampling. In practice, however, the actual overlap of sampling areas was
relatively limited (see Results). This was due to: substantial 3-dimensional habitat complexity at
most sites, habitat width > 1 m (typically over 2 m), and ever-present wave action that caused
inshore-offshore sway of the reference line. Nonetheless, at each survey site belt transects were
conducted prior to quadrat sampling to eliminate confounding effects of the latter on the former.

Field observations suggested that whelk population structure was influenced by the physical
energy of their habitat (sensu Debrot 1990b). This was examined further in two ways. First, we
did apost-hoc analysis of our dataset in which each site was placed into one of three categories
(Bays, Points and Cays) based upon predominant coastal morphology and a subjective
assessment of exposure to prevailing seas. Second, we utilized a deliberate sampling strategy at a
limited number of sites to test the hypotheses that whelk populations would have greater average
size and lower population density in habitats exposed to high wave energy, and that whelk would
have smaller average size and greater population density in comparatively sheltered habitats. Our
paired-sample design consisted of 1) a sample from a relatively exposed coastline (e.g. rocky






SEAMAP-C: USVI Whelk Survey Final Report


headland) and 2) a matched sample from an adjacent but relatively protected coastline (e.g. bay).
For each pair, the two samples were taken less than 600 m apart. Six replicate sites (four on St.
Croix and two on St. John) were surveyed by paired-sampling: Hughes Point (HP-1 and HP-2),
Europa Bay (EU-1 and EU-2), Buck Island (BI-1 and BI-2), Whistling Cay (WST-1 and WST-
2), Pull Point (PP-1 and PP-2), and Long Point West (LPW-1 and LPW-2). Replicate sites
(independent pairs) were separated by > 5 km, and each represents a unique combination of
exposure to wind, seas, and swell. The difference in physical energy within and among pairs was
not measured.

Data Analysis

Raw survey data were entered into Microsoft Excel for manipulation and graphical analyses.
Statistical analyses were performed with Statistica (Statsoft, Inc., Tulsa, OK). For inter-island
comparisons, data were pooled by island group (northern vs. southern islands) and tested with a
Students t-test (two-tailed, assuming unequal variance). For inter-habitat comparisons of size and
abundance, data were pooled by group and tested with a one-way ANOVA. Data for paired-site
comparisons were pooled by group and tested with a two-tailed Students t-test, assuming unequal
variance.

To estimate the number, density and percentage of reproductively mature individuals in samples,
an estimate of C. pica size at first reproduction was required. Review of the literature showed
great inconsistency. For the USVI, Randall reported that the smallest male and female C. pica
she observed were, respectively, 32.4 mm and 33.7 mm shell length (as measured from tip of
spire to distal lip). In Costa Rica, Schmidt et al. (2002) calculated C. pica mean size at first
maturity to be 29.2 + 1.1 mm shell length (as measured across widest diameter at base of shell).
Debrot (1990b) presented gonadal index data for C. pica from the Bahamas that compounds the
discrepancies among reported measures. In the absence of a clear consensus, an intermediate
value of 30.5 mm shell width was selected and applied to the data for this analysis (i.e., all C.
pica> 31 mm shell width were considered reproductively mature).

In order to make comparisons to historic data from Henley Cay and Cockroach Island (Clavijo et
al. 1984), our datasets for HEN and CRI were modified as follows. For each, quadrat data was
scaled proportionally to belt transect survey area (100 m) and the two types of data were pooled
to generate a combined frequency distribution. Because historic data for Henley Cay and
Cockroach Island did not contain information on whelks < 20 mm shell width (Clavijo et al.
1984), these size classes were excluded from contemporary data sets to generate comparable size
frequency distributions. We note that the historic collections done at Henley Cay and Cockroach
Island were not quantitative (a CPUE method was used, but amount of effort was not reported).
This precludes comparisons of absolute abundance or density.


Results

Between June of 2003 and May of 2004, whelk populations were surveyed at 41 areas in the
USVI (Figures 1 and 2, Table 3). In the northern islands (St. Thomas and St. John), 26 surveys






SEAMAP-C: USVI Whelk Survey Final Report


were conducted at 24 areas. In St. Croix, 21 surveys were conducted at 17 areas. Six of the
survey areas were paired-site comparisons conducted at St. Croix (4 pairs) and St. John (2 pairs).

In quadrat surveys, a total of 4,722 C. pica were observed (1,880 on St. Croix and 2,842 on St.
Thomas and St. John). In belt transects, a total of 593 individuals were observed (249 on St.
Croix and 344 on St. Thomas and St. John). Undersized individuals (<62 mm shell width) were
also incidentally collected in belt transects on St. Croix (n = 6) and on St. Thomas and St. John
(n = 103). These data were excluded from subsequent analyses but are presented in Appendices.

Whelks were common in most quadrat samples. Average density by island group was 7.5 and 8.9
individuals per m2, for southern and northern islands, respectively. These densities were not
significantly different between island groups (Table 4). Density estimates varied considerably
among sites, both within and between island groups, as indicated by a high variance-to-mean
ratio (9.9 to 20.4, Table 4).

Harvest-size whelks (> 62 mm shell width) were comparatively uncommon in belt transect
surveys. Average density of harvest-size individuals by island group was 7.3 and 6.6 individuals
per 50 m2 for southern and northern groups, respectively (Table 4), or about 1/50th of the total
population density (as estimated from quadrats). Differences in density of harvest-size C. pica
between island groups were not significant (Table 4) and the data were also characterized by a
high variance-to-mean ratios (>15, Table 4).

Whelk body size also varied considerably among sites. Based upon quadrat data, this difference
was significant between island groups (P < 0.001, Table 4). Size frequency distributions (Figure
3A,B) for data pooled by island group show that St. Croix populations are characterized by both
a smaller median size (- 20 mm shell width; Table 4) and a proportionately broader size range of
large whelks (> 70 mm shell width) at low frequency. A marked decline in the relative
abundance of 35-40 mm size classes was observed for both island groups (Figure 3A,B),
suggesting that mortality of whelks increases substantially in this age group. Collectively,
reproductively mature individuals ( 31 mm) comprised 16.3 % and 24.5 % percent of these
samples for southern and northern island groups, respectively. Although pooling data (e.g. Figure
3) largely obliterates the identification of annual cohorts, whelk size distributions from
individual sites (see Appendices 3-5) often showed two or more distinct size class peaks.

Results from belt transect surveys showed a significant difference in whelk body size between
island groups (P < 0.001, Table 4). On average, harvest-size adults were larger on St. Croix (85.3
mm) than in the northern islands (78.6 mm). Size frequency distributions of harvest-size whelk
are shown in Figure 4A,B).

Site-to-site variability in C. pica size and abundance was pronounced (e.g. Appendices 1 and 2)
and a negative (though not significant) relation was observed between average body size and
average density (Figure 5A,B). A comparison across three broad habitat types (bays, points,
cays) revealed significant differences (Table 5) in whelk population structure. In bays, whelks
were more abundant and had a smaller average size than at points or cays. Harvest-size whelks
were rare in bays (0.65 individuals/50m2) and were most abundant at cays (11.4 individuals/m2;






SEAMAP-C: USVI Whelk Survey Final Report


Table 5). This relation was examined further in paired-sampling (Figure 6A,B). Whelk on
windward (exposed) sides of points and cays were larger, on average, than whelks on Leeward
(protected) sides. Total whelk density was higher on leeward sides than windward sides. At some
sites, the leeward side had substantially more whelk young of the year (HP-2, EU-2, WST-2,
LPW-2; see Appendix 6). At half the sites, the density of harvest-size whelk was greater on the
windward side [HP-1, EU-1, WST-1].

To examine the reproductive status of studied populations, we used belt transect data and quadrat
data for each site. The abundance of larger whelk (> 62 mm shell width, presumably all mature)
was compared to the abundance of small reproductive individuals (L31 mm shell width) as
derived from quadrat data. These measures showed a weak positive relation for northern and
southern island groups (St. Croix, r2 = 0.784; St. Thomas and St. John, r 2 = 0.21). Site
accessibility was plotted onto these data for whelk reproductive status (Figure 7). Sites that were
either restricted to casual access or to harvesting had whelk populations with a higher proportion
of reproductive individuals (Figure 7) compared to those sites where access was easy.

Sampling was conducted over the course of almost one year, enabling us to examine our data for
evidence of seasonal trends in abundance of C. pica young of the year (YOY). We did not
observe individuals smaller than 2 mm in our sampling. Assuming that C. pica recruits reach a
size of 4-5 mm at about 6 months of age (calculated from Randall 1964 and Bell 1992) we used a
minimum size of< 5 mm to identify YOY in our collections. On St. Croix, a single, distinct peak
in YOY density was observed during spring sampling (Figure 8A). Otherwise, in St. Croix
samples YOY were only observed at relatively low densities (< 0.2 individuals/m2). On St.
Thomas and St. John, a more pronounced abundance peak of YOY was also observed in spring
samples, with additional smaller peaks during the winter (Figure 8B). We note that small whelks
could be observed sporadically throughout most of the year-long study period (e.g. Appendix 1).

We compared historic USVI surveys of C. pica populations at Henley Cay [HEN] and
Cockroach Island [CRI] to data obtained in this study. Size frequencies of whelk from HEN were
comparable to data from c. 1981 (Figure 9A). Whelk size frequencies at CRI show pronounced
differences (Figure 9B), and suggest that average size has decreased substantially at this site.

Anecdotal Observations

Size-specific zonation of C. pica has been observed previously on St. John (Randall 1964,
Boulon 1987), Barbados (Lewis 1960), Bahamas (Debrot 1990a), and Costa Rica (Schmidt et al.
2002). Although not quantified in this study, we made similar observations. Generally, the
youngest size classes (2-8 mm shell width) were observed higher in the intertidal while larger
individuals (> 80 mm shell width) were observed below mean low water. Often these larger
whelks were deep within crevices or under boulders.

Evidence of predation on C. pica was seen rather infrequently at several sites during these
surveys. Shoreline feeding activities of American oystercatchers (Haemotopus ostralegus) were
deliberately interrupted to examine the size of whelk upon which they were feeding. Three
species of gastropods were observed preying upon C. pica in the intertidal zone: the wide-






SEAMAP-C: USVI Whelk Survey Final Report


mouthed rock drill (Purpurapatula), the deltoid rock drill (Thais deltoidea) and another
unidentified species of rock drill (Thais sp.). Octopus predation on C. pica was implicated by
shells found adjacent to octopus caves. Most observations indicated that predation was directed
towards young adult whelks (c. 25-35 mm shell width) and no instances of natural predation on
harvest-size individuals were observed.


Discussion

Randall (1964) stated that Cittarium pica is "probably the most common large gastropod of the
exposed rocky littoral region" in the West Indies. Our study confirms that small individuals of C.
pica may be locally quite common, especially in bays and semi-protected habitats. Our results,
however, do not indicate that "large" individuals of C. pica are particularly common in the USVI
and, similar to reports from elsewhere (e.g. Clench and Abbott 1943, Flores 1981, Schmidt et al.
2002), we found them to be a rare fraction of the total population at most sites.

The abundance and size of whelk was highly variable among sites. Whelk density was not
significantly different between northern and southern island groups in the USVI. Average size
was different between north and south, and although this observation might be attributed to
differing fisheries, a cautious interpretation is recommended. As discussed below, we feel that
habitat is such a powerful modifying factor on the structure of whelk populations that definitive
conclusions about inter-island size differences should adequately account for an unequal
distribution of habitat types among those islands.

In this study, we considered only one aspect of whelk habitat the relative degree to which an
intertidal shoreline is exposed to physical wave energy and this is clearly an oversimplification
of numerous biotic and abiotic factors influencing whelk populations. Nonetheless, the relation
between whelk size and exposure, as suggested previously (Randall 1964, Clavijo et al. 1984),
was quite evident along gradients of habitat exposure: sheltered bays had high densities of almost
exclusively small whelk, while at the other extreme, some exposed cays or points had remarkable
stands of large adult whelks. Debrot (1990b) also identified wave action as a significant factor
modifying Bahamian whelk populations; however he showed a negative relationship between
body size and exposure. We found the opposite: increased exposure was positively related to
whelk body size. It is highly likely that site exposure to high seas limits access by fishermen,
thereby creating harvest refugia which enable C. pica to reach a larger average size.

In comparison to exposed coastlines, juveniles of C. pica were relatively abundant on
leeward/protected shorelines. This observation suggests greater recruitment of whelk to leeward
shores. Caselle and Warner (1996) observed an increase in recruitment of reef fish larvae to
leeward sites on St. Croix which they attributed to physical transport processes. Alternatively,
whelk may suffer lower mortality rates during their early post-settlement period at such sites.
Large adult whelk could conceivably reduce densities of their conspecific recruits by incidental
grazing, as has been suggested for some species of abalone (Naylor and McShane 2001). A third
possibility still is that adult grazing modifies resident algal communities to which whelk larvae
are cued for settlement, but no such cues are presently known (Bell 1992).






SEAMAP-C: USVI Whelk Survey Final Report


The striking spatial variability that we observed may have implications for stock management.
Similar to abalone, whelk may exist as metapopulations (Mayfield et al. 2001). Whelk share
many life-history attributes that create sub-structuring of abalone populations, and not
coincidentally also contribute to their vulnerability to overharvesting. Whelk habitat is a narrow
intertidal band which is generally accessible to humans. Whelks have extremely low mobility -
in tagging studies, adults were observed to move < 100 m over 6 months (Randall 1964, Debrot
1990a). Their larvae have a very short planktonic duration of 2.5 to 5 days (Bell 1992) that
potentially greatly limits their dispersal capacity. Whelk may also be susceptible to an Allee
effect (Quinn et al. 1993) where fertilization success drops dramatically when adult density is
reduced below a threshold value, leading to catastrophic population collapses but presently too
little is known of whelk spawning [see below] to determine if such effects occur. Taken together,
these factors would indicate that C. pica might best be managed as a mosaic of partially isolated
groups.

The reproductive biology of whelk has not received much attention. It is assumed that sexes are
separate in C. pica. Their fertilization is external, and Bell (1992) gives an account of C. pica
spawning observed in aquaria in the Bahamas. Apparently, there are no seasonal or interannual
observations for whelk spawning in the USVI, although circumstantial evidence can be drawn
from recruitment patterns. Randall (1964) observed a pronounced recruitment of very small (-1
mm) C. pica in January. Boulon (1987) saw an influx of April "post-recruits" at Windswept
Beach, St. John. Bell (1992) observed a C. pica recruitment pulse in the Bahamas from January
to May, and used larval growth rates to show that recruits originated from a spawning in early
October. Bell (1992) also calculated that an October spawning date would explain the timing of
whelk recruitment observed by Randall on St. John. In our surveys, whelk young-of-the-year
(YOY) were most abundant in spring. Our data are not recruitment patterns per se, as spatially-
distributed sampling may confound temporal patterns. The data are nonetheless consistent with
an annual peak spawning of C. pica that occurs in autumn.

In the USVI, the annual 6-month closed season on whelk harvesting reopens on October 1 of
each year. The foregoing information indicates that this reopening date should be re-evaluated
carefully with data for USVI whelk populations. An October reopening date may be tragically
close to the annual peak spawning date for C. pica, and thus may be particularly ineffective in
protecting spawning stocks. The relation of reproductive output to body size has not been studied
in whelks (but see Debrot 1990b for gonadal indices), however it is assumed that large
individuals contribute disproportionately to total reproductive output (Boulon 1987). Adequate
protection of whelk stocks through their [actual] peak spawning period would add a measure of
security against recruitment failure.

Our quantitative whelk surveys are presented here as a baseline for population density in the
USVI. Over a timescale of four to five decades, it seems probable that our "baseline" whelk
populations have dropped precipitously from historic values a phenomenon called shifting
baseline syndrome (Pauly 1995). In southern California, for example, declines in average body
size of intertidal gastropods began almost 40 years ago (Roy et al. 2003) and our only available
comparisons (from 1980's, Figure 9B) also suggests a trend towards decreased body size in C.






SEAMAP-C: USVI Whelk Survey Final Report


pica. Accounts from the USVI dated earlier (c. 1960) suggest that whelk were once vastly more
abundant. "Whelks were so plentiful twenty years ago along the rocky edges of the north or
northwest shoreline off St. Croix, that it was dangerous to walk on the rocks; you would slip on
the whelks as they slid out from under your feet. Ten years ago, they were gone from above the
waterline, but you could catch them at night with a light. Today to find whelks, you must dive,
and then you are lucky to find any." (T. Skov quoted in deGraff and Moore 1987). In the 1950's
and 60's, a person could wade through the intertidal zone at Sprat Hall and easily fill a sack with
large whelk (H. Rivera, pers. comm.). Today these abundances seem almost unimaginable our
surveys at these same areas [NTP, MAH, SPH] revealed few large whelk. Unfortunately,
quantitative data for this time period do not exist and reconstruction of pre-exploitation
abundances (e.g. Rogers-Bennett et al. 2002) is probably not possible. It is unlikely we will ever
know how robust these historic whelk populations actually were.

Marine Protected Areas (MPAs) are an attractive possibility for management of C. pica
populations. In Costa Rica, C. pica populations within an MPA were substantially larger and
more abundant than at sites where harvesting is chronic (Schmidt et al. 2002). Three of our sites
were within MPAs (BI-1, BI-2, ROT) and densities of large C. pica were comparatively high
(Figure 7). The highest densities of large whelk, however, were observed outside of formal
MPAs, but in areas where harvesting is restricted or reduced. At Hovensa Breakwater (HOV),
fishers are excluded for shipping security reasons and robust populations of adult whelks were
found there. Similarly, Flanagan Island (FLA) had remarkable populations of large adult whelks.
FLA is thought to be only lightly harvested because of uncertainty over jurisdictional control,
distance from population centers, and exposure to seas (S. Gordon, pers. obs.). The latter two
sites (HOV, FLA) may function as defacto marine reserves, similar to reserves in British
Columbia where abalone populations benefited from inadvertent harvest restriction (Wallace
1999). These observations suggest that MPAs could protect whelk populations, adding a
safeguard against possible Allee effects (Quinn et al. 1993). However, some authors report that
the effective protection of desirable intertidal invertebrates requires that humans are physically
excluded from those environments (Castilla and Duran 1985, Keough and Quinn 2000, Roy et al.
2003). It is improbable that such strict measures would ever gain acceptance in the USVI.

How effective are existing whelk management policies of minimum harvest size and closed
season? Insufficient information exists to make any definitive conclusions. The dates for whelk
closed season should be re-evaluated after data are collected on spawning activities of whelk in
the USVI. Our data also suggest that the minimum harvest size is not widely observed. At the
majority of our sampling sites, size-frequency distributions showed an abrupt truncation in body
size at 35-40 mm shell width suggesting that, at many sites, whelk mortality increases sharply
in approximately their 3rd year. Natural mortality (due to predation) seems an unlikely
explanation as it was only infrequently observed and was apparently directed towards smaller
size classes of whelk. Harvest by fishers may be the primary source of mortality for larger size
classes of C. pica (Boulon 1987) and our data suggest that fishing mortality extends to
individuals that are considerably smaller than the legal minimum harvest size.

Worldwide, declines or collapses of fisheries for nearshore marine invertebrates are now
commonplace (Jackson et al. 2001, Leiva and Castilla 2002). Mannino and Thomas (2002)






SEAMAP-C: USVI Whelk Survey Final Report


reviewed a number of factors that influence the susceptibility of intertidal gastropods to stock
depletion. Two factors seem applicable to the persistence of whelk populations despite the as yet
unquantified level of harvesting. First, C. pica appears to attain reproductive maturity at a young
age (- end of its second year) and small size, whereas their meat yield is low until about their
third year (see Clavijo et al. 1984 for a shell width-meat weight curve). Second, harvest refugia
may have maintained pockets of large whelk at high density, ensuring successful spawning and
recruitment despite localized depletions of larger whelk from more accessible areas.


Data Needs

- There is a critical need to collect accurate information on seasonal reproductive patterns of C.
pica in the USVI. In particular, timing of annual spawning activity needs careful study. A
relatively straightforward study design (Bell 1992) conducted at a small number of sites among
islands would potentially yield vital information for evaluating the closed season on whelk.

- Further studies should be conducted on the reproductive biology of C. pica in the USVI,
including minimum size and age at reproductive maturity, the relation between reproductive
output and age/size, spawning behavior, and fertilization success in relation to population
density.

- There is a clear need for more information about the harvest of whelk in the USVI. Fishery-
dependent data from commercial and recreational sectors (see Clavijo et al. 1984) are needed to
estimate their relative contribution to C. pica harvest. As with many other rocky intertidal
invertebrates (e.g. Keough and Quinn 2000), other forms of take such as subsistence harvesting
or collecting for fishing bait may also be of considerable impact to C. pica populations.

- The degree of compliance with existing regulations should be evaluated. Action should be
taken to inform and educate groups that are prone to non-sustainable whelk harvesting practices.

- There is a need to understand the USVI whelk fishery in a wider geographic context. Only one
published account of a whelk fishery is available (Schmidt et al. 2002). Instances of localized
extirpations have been cited (Carter 2002) without detail. Resource managers would benefit from
a Caribbean-wide comparison to identify best- and worst-case scenarios for whelk management.

- Whelks present an unusual opportunity for an integrated study of recruitment/dispersal in
relation to population genetics (sensu Taylor and Hellberg 2003 but with a commercially
important organism). These data would be directly applicable to resource management.

- Establishment of a whelk monitoring program is considered a low-priority item. Usefulness of
monitoring data will depend critically upon prior quantification of whelk exploitation (known
fishing effort, harvest patterns, size preferences, etc.) and parallel advances in our knowledge of
C. pica biology (see above). Such basic biological information should inform study design. For
example, whelk generation time should dictate the sampling frequency of a monitoring study.
However, the maximum lifespan of C. pica is largely unknown [a minimum estimate of > 6.5






SEAMAP-C: USVI Whelk Survey Final Report


years comes from Randall's (1964) observations on a single individual of 93 mm shell length].
The design of future monitoring studies must recognize the limitations imposed by such
unknowns. Study design should also include sites within new or proposed MPAs and should use
explicit stratified sampling with survey sites chosen based upon specified monitoring objectives.
These objectives should be closely tied to realistic options for management action to conserve
whelk stocks.


Acknowledgments

This study was funded by grant No. NA03NMF4350100 from Southeast Area Monitoring and
Assessment Program Caribbean (SEAMAP-C) to Division of Fish and Wildlife. The essential
(oftentimes courageous) participation of many people in whelk surveys is gratefully
acknowledged: Ursula Anlauf, Larry Aubain, David Camoyan, William Coles, Ruth Gomez,
Michael Holt, Luke Johnson, Sharky Marin, Jennifer Messineo, Hector Rivera, Ron Sjoken,
William Tobias, Roger Uwate, Jason Vasques, Willy Ventura, Digna Washington, and Kim
Woody. Zandy Hillis-Star and Raphe Boulon helped obtain permits to conduct studies within
Buck Island Reef National Monument and Virgin Islands National Park, respectively. Dave
Watterson is gratefully acknowledged for coordinating access to Hovensa, L.L.C., East
Breakwater and for assisting with surveys there. This manuscript was improved by comments
from Barbara Kojis, Christine O'Sullivan, Roger Uwate, and Jason Vasques.






SEAMAP-C: USVI Whelk Survey Final Report


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SEAMAP-C: USVI Whelk Survey Final Report


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Mannino, M.A. and K.D. Thomas (2002) Depletion of a resource? The impact of prehistoric
human foraging on intertidal mollusk communities and its significance for human settlement,
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Publication No. 8, West Indies Laboratory, Teague Bay, St. Croix, USVI. 213 pp.

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iris (Mollusca: Gastropoda) caused by conspecific adults and wave exposure. New Zealand J.
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10:430.

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Amer. Zool. 33:537-550.

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topshell, Cittarium pica (Linnaeus). Bull. Mar. Sci. Gulf and Carib. 14(3):424-443.

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abundances of abalone in California for restoration. CalCOFI Rep., Vol. 43:97-111.

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and historical decline in body size of rocky intertidal gastropods of southern California.
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Schmidt, S., M. Wolff and J.A. Vargas (2002) Population ecology and fishery of Cittarium pica
(Gastropoda: Trochidae) on the Caribbean coast of Costa Rica. Rev. Biol. Trop. 50(3-4):
p.1079-1090.

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SEAMAP-C: USVI Whelk Survey Final Report


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SEAMAP-C: USVI Whelk Survey Final Report


List of Tables and Figures


Table 1. USVI whelk areas identified by commercial fishers

Table 2. Comparison of two methods at Sprat Hall: quadrats and cross-shore transects

Table 3. Survey sites

Table 4. Results of Inter-island group comparison

Table 5. Results of ANOVA to test for inter-habitat differences

Figure 1. Map of Cittarium pica survey sites on St. Croix

Figure 2. Map of Cittarium pica survey sites on St. Thomas and St. John

Figure 3. Size Distributions by Island, Quadrat Data
A. St. Croix B. St. Thomas and St. John

Figure 4. Size Distributions by Island, Belt Transect Data
A. St. Croix B. St. Thomas and St. John

Figure 5. Scatter plot of average size vs. average density
A. St. Croix B. St. Thomas and St. John

Figure 6. Cittarium pica at six exposed vs protected sites
A. Abundance B. Size

Figure 7. Relation of reproductive capacity to site access
A. St. Croix B. St. Thomas and St. John

Figure 8. Young of the Year
A. St. Croix B. St. Thomas and St. John

Figure 9. Comparison to historic data
A. Henley Cay B. Cockroach Cay

Appendix 1. Summary of quadrat data by site
Appendix 2. Summary of belt transect data by site
Appendix 3. Size distribution at St. Croix sites
Appendix 4. Size distribution at St. Thomas sites
Appendix 5. Size distribution at St. John sites
Appendix 6. Size distributions at paired sites






SEAMAP-C: USVI Whelk Survey Final Report



Table 1. Areas of abundant whelk (Cittarium pica) as identified by USVI commercial fishers.
Fisher Survey
Area Name Score* Site


St. Thomas Fishers 18 respondents
(13 areas) Salt and West Cays 10 +
Outer Brass (Rough Pt. and west side) 8
Dog Island 7 +
Saba Island (west & south side) 6 +
Cockroach Island 5 +
Little Hans Lollick (north-northeast side) 5 +
Sprat Point on Water Island 5 +
Savana Island (south-southwest side) 4
Coculus Rocks and Rotto Cay 2 +
Great Thatch Cay (north side) 2 +
Hassel Island (south side) 2 +
Little St. James (north side) 1
Mandal to Magens Bay Point 1 +

St. John Fishers 3 respondents
(6 areas) Flanagan Island 2 +
Leduck Island 2
Ram Head to Nanny Point 2 2 +
Reef Bay 2 +
Waterlemon Cay 1 +
Whistling Cay 1 +

St. Croix Fishers 10 respondents
(13 areas) East Point (a.k.a. Point Udall) 7 +
Hovensa Breakwater 5 +
Annaly Bay 3 +
Barons Bluff 2 +
Hams Bay 2 +
Hams Bluff to Maroon Hole 2 +
Hughes Point 2 +
Lamb Bay 2
Tidepools on NW Shore 2 +
Buck Island 1 +
Grassy Point 1 +
Grapetree Point 1 +
Sprat Hall to Butler Bay 1 +


* Fisher score refers to the number of fishers who said an area has or had a substantial population of whelk.
1 Little Hans Lollick was surveyed on the south side only
2 Ram Head was surveyed on the western (leeward) side only






SEAMAP-C: USVI Whelk Survey Final Report


Table 2. Comparison of methods for surveying Cittarium pica: cross-shore transects and quadrats.


Method
Cross-Shore Transect (Boulon 1987) Quadrat
General attributes
Primary Advantage Samples integrate across intertidal zones Values are comparable among different sites

Primary Disadvantage Cumbersome in rough seas Inshore-offshore quadrat placement is subjective
Transect length is not pre-defined

Unit of Observation 1.0 m-wide strip of variable length 1.0 m2 quadrat
Oriented perpendicular to shore Placed in zone of highest C. pica abundance

Unit of Abundance Linear (No. Individuals / m shoreline) Density (No. Individuals / m2)

Results from Sprat Hall Surveys
No. of Observations 20 cross-shore transects 20 quadrats
Total No. of Cittarium 149 70
Average Abundance 7.45 / m shoreline 3.50 / m2
St.Dev. 6.45 5.20
SEM 1.44 1.16
95% Confidence Interval 4.4 to 10.5 1.07 to 5.93
Range 0 to 25 0 to 19

Estimated Population Size* 745 Individuals 889 Individuals
95% Confidence Interval 442 to 1,046 271 to 1,506

* In order to compare cross-shore transect data (a linear measure) to quadrat data (a density measure), the observations had to be scaled to an appropriate
value. This was the estimated population size [EPS] of whelk within the 100 m-long study area at SPH. Cross-shore transect data were multiplied by 100 m
(i.e. the length of shoreline) to obtain EPS. For quadrat data, EPS was calculated as follows: whelk density x shoreline length x intertidal habitat width.
Intertidal habitat width was measured at each of the 20 quadrat sampling positions and yielded an average width of 2.54 m + 1.78 (St.Dev.







SEAMAP-C: USVI Whelk Survey Final Report


Table 3. Survey sites.
Survey Location
Site Name Site Code Survey Date Lat (N) Long (W)
St. Croix
Sprat Hall SPH 20 Jun 03 17 44.391' 640 53.533'
Hams Bay HAM 23 Jun 03 170 46.049' 640 52.893'
Barons Bluff BRB 15 Aug 03 170 46.990' 640 46.575'
Long Point, East LPE 3 Oct 03 170 40.931' 640 50.046'
Annaly Bay ANB 22 Oct 03 170 45.829' 640 50.602'
Knights Bay KNB 24 Oct 03 170 45.439' 640 35.425'
Grassy Point GRP 28 Oct 03 170 43.987' 640 36.596'
Grapetree Point GTP 29 Oct 03 170 44.710' 640 35.837'
Watch Ho WHP 31 Oct 03 170 41.931' 640 43.122'
East Point EPT 21 Nov 03 170 45.284' 640 33.883'
Buck Island-1 BI-1 25 Nov 03 17 47.255' 640 36.685'
Buck Island-2 BI-2 25 Nov 03 170 47.191' 640 36.729'
Hovensa Breakwater HOV 29 Dec 03 170 41.275' 640 44.416'
Hughes Point-1 HP-1 29 Mar 04 170 44.697' 640 35.126'
Maroon Hole MAH 5 Apr 04 170 46.140' 640 52.000'
NW Tidepool NTP 7 Apr 04 17 45.980' 640 51.515'
Long Point, West-1 LP-1 15 Apr 04 170 40.813' 640 50.263'
Long Point, West-2 LP-2 15 Apr 04 170 40.799' 640 50.333'
Hughes Point-2 HP-2 26 Apr 04 170 44.728' 640 35.213'
Pull Point-1 PP-1 28 May 04 170 45.918' 640 39.298'
Pull Point-2 PP-2 28 May 04 170 45.856' 640 39.296'

St. Thomas
Rotto Cay ROT 16 Oct 03 180 18.791' 640 51.924'
Dog Island DGI 17 Oct 03 180 17.698' 640 48.831'
Secret Harbor SEC 18 Oct 03 180 19.117' 640 51.193'
Thatch Cay THC 21 Oct 03 180 21.681' 640 51.173'
Salt Cay SLT 23 Oct 03 180 21.581' 650 03.024'
Stumpy Bay STB 23 Oct 03 180 21.802' 650 00.543'
Water Island WAT 30 Oct 03 180 19.076' 640 56.605'
Hassel Island HAS 30 Oct 03 180 19.539' 640 56.144'
Little Hans Lollick LHL 31 Oct 03 180 24.434' 640 54.493'
Inner Brass IBR 31 Oct 03 180 23.077' 640 58.526'
Saba Island SAB 4 Nov 03 180 18.336' 650 00.146'
Lovango LOV 20 Jan 04 180 21.765' 640 47.894'
Cockroach Island CRI 7 May 04 180 24.192' 650 03.543'
Mandal MAN 27 May 04 180 21.783' 640 53.951'

St. John
Turner Bay TUR 21 Oct 03 180 19.285' 640 47.694'
Flanagan Island FLA 24 Oct 03 180 19.636' 640 39.168'
Reef Bay RFB 13 Jan 04 180 19.402' 640 44.830'
Round Bay RND 14 Jan 04 180 19.769' 640 40.611'
Europa Bay-1 EU-1 16 Jan 04 180 18.947' 640 43.912'
Henley Cay HEN 16 Jan 04 180 21.176' 640 47.453'
Waterlemon Cay WLM 22 Jan 04 180 22.060' 640 43.404'
Whistling Cay-1 WST-1 9 Mar 04 180 22.218' 640 45.550'
Whistling Cay-2 WST-2 30 Mar 04 180 22.161' 640 45.409'
America Point AMP 30 Mar 04 180 21.479' 640 45.088'
Ram Head RAM 2 Apr 04 180 18.003' 640 42.220'
Europa Bay-2 EU-2 26 Apr 04 180 19.095' 640 43.512'






SEAMAP-C: USVI Whelk Survey Final Report


Table 4. Comparison of Cittarium pica density and size between northern and southern islands groups of the USVI.


Density


Quadrat (No./m2)


Belt (No./50 m2)


Size (shell width,
Quadrat Method


mm)
Belt Transect


Island Group1


STX


STT+J


STX


Mean


Variance

Var/Mean ratio

St. Dev.

Observations

df

t Statistic

P(T<=t) two-tail

t Critical two-tail

Significance


73.7

9.9

8.6


-1.535

0.125

1.964


180.8

20.4

13.4


113.7

15.5

10.7


STT+J

6.6

103.7

15.7

10.2


0.306

0.760

1.995


STX

20.7


STT+J

22.2


197.7 185.7


9.5

14.1

1880

3935

-3.448

0.001

1.961


8.4

13.6

2842


ns


Method


STX

85.3

160.6

1.9

12.7


STT+J

78.6

87.8

1.1

9.4


344


7.341


< 0.001


1.964


1 Data were pooled by island group: STX = St. Croix, STT+J = St. Thomas, St. John, and associated cays.
An asterisk (*) indicates a significant difference (P < 0.05) using Students t-Test (two-Sample, assuming unequal variances, hypothesized mean
difference =0, two tailed test).and an nii' indicates not significantly different at the 0.05 probability level.







SEAMAP-C: USVI Whelk Survey Final Report


Table 5. Results of ANOVA to test differences in Cittarium pica population structure among three types of coastline.


Comparison Groups'


Count Sum Avg Var Source
of Variation


df MS F P-value F crit


Abundance
(quadrats)


Abundance
(belt transects)


Body Size
(quadrats)


Body Size
(belt transects)


I. Bay
II. Point
III. Cay

I. Bay
II. Point
III. Cay

I. Bay
II. Point
III. Cay

I. Bay
II. Point
III. Cay


1446
1183
972


1446
1183
972

13
221
318

28453
25202
28709

996
18143
25433


10.63
6.65
5.25

0.65
8.50
11.36

19.68
21.30
29.54

76.62
82.10
79.98


186.97
43.35
65.88

2.13
128.10
138.68

64.23
242.46
272.28

80.26
152.50
105.97


Between Groups
Within Groups
Total

Between Groups
Within Groups
Total

Between Groups
Within Groups
Total

Between Groups
Within Groups
Total


2357.2
45035.4
47392.6

1380.9
6987.5
8368.4

60836.5
643784.0
704620.5

811.6
68106.9
68918.5


2
3598
3600


1178.6 12.981
90.8


690.4 7.016
98.4


30418.3170.003
178.9


405.8 3.271
124.1


0.000 3.014

*

0.002 3.126

*


0.000


2.998


0.039 3.012


An asterisk (*) indicates a significant difference (P < 0.05) and "ns" indicates not significantly different at the 0.05 probability level.

SFor this analysis, survey sites were classified by coastline morphology and sea exposure into one of three groups: I. Bay (embayments,
leeward or semi-protected coastlines, and tidepools), II. Point (points, headlands and exposed open coastlines) or III. Cay cayss and small
islands, offshore islands). Group I sites were: SEC, WAT, RFB, HAS, RND, TUR, STB, KNB, HAM, SPH, and NTP (n =11). Group II sites
were: LPE, WHP, MAH, GRP, HP-1, EU-1, HOV, EPT, AMP, GTP, ANB, RAM, BRB, PP-1, and LP-1 (n= 15). Group III sites were: LHL,
LOV, WLM, SAB, FLA, IBR, BI-1, WST-1, SLT, ROC, CRI, HEN, THC, and DGI (n = 14). Paired sampling sites (EU-2, PP-2, WST-2, BI-
2, LPW-2, HP-2) were excluded. MAN was also excluded because surveys there spanned two habitat categories (tidepools and exposed open
coastline).







SEAMAP-C: USVI Whelk Survey Final Report


Figure 1. Location of sites for surveying Cittarium pica populations on St. Croix, U.S. Virgin Islands. Sites are indicated with closed
circles and numbers (see text for site names). Four paired-sampling sites are shown with open circles. Map redrawn from Kendall et
al. (2001).


BI-1
BRB
- f1 BI-2


HOV


Legend


0 1 2 4 6 8


* sample sites
o paired sites


Kilom eters


. ..






SEAMAP-C: USVI Whelk Survey Final Report


Figure 2. Location of sites for surveying Cittarium pica populations on St. Thomas, St.John and associated cays of the northern U.S.
Virgin Islands. Sites are indicated with closed circles and numbers (see text for site names). Two paired-sampling sites are shown with
open circles. Map redrawn from Kendall et al. (2001).


ct LHL

z



1131


RAM


Legend
* sample sites
o paired sites


0 1 2 4 6 8
. .Kilometers


J b


SLT i


THC A,-LOV
TII C f ^' ,








SEAMAP-C: USVI Whelk Survey Final Report


Figure 3. Size distribution of Cittarium pica obtained in quadrats. Quadrat data were

pooled by island group. A. Southern island of St. Croix (21 surveys). B. Northern islands

of St. Thomas, St. John, and associated cays (26 surveys).


0.25



0.20



S0.15
U


0.10
LL


0.05



0.00










0.25



0.20



0.15

(,

0.10
LL


0.05



0.00


o 0 0 t 0 0 0 t 0 0 0 t 0 0 0 t o C
(I (- M- 04 0 (0 (0 o- N- CO CO 0) C C) 0 0
C) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 E

LO M 04 04 ( ) (' L t t e D N- C C M e

Shell Width (mm) 0


) o t o t o t o t o t o0 t 0 0 0 t 0o 0 )
- 4- 4- 0M 0M 'I 'I U) U t t (0 (0 N- N- CO CO ) C) 0 0
C) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 E 2

SM M 'IT 'T (Shell Width( 0 0 (mm)O
Shell Width (mm) 0









SEAMAP-C: USVI Whelk Survey Final Report







Figure 4. Size distribution of Cittarium pica obtained in belt transects. Only individuals

> 62 mm shell width (harvest-size) are presented. Belt transect data were pooled by

island group. A. Southern island of St. Croix (19 surveys). B. Northern islands of St.

Thomas, St. John, and associated cays (26 surveys).


0 20


U
S015

0*

010



0 05



0 00


A. St. Croix


0 LO

(D


0 LO
D
0 0
(D


0 LO
0) 0)
0 0
(DCo
0 Y0)


D 8
o o
M D


n249


D a)
0
0 E
Co 0
D


Shell Width (mm)


B. St. Thomas and St. John


8D
0 0

CO Co


Shell Width (mm)


0 30



0 25



S020


U
S015



S010



0 05



0 00


n=344


0 0

(0 (0


DD
0 0
co

T- (D







SEAMAP-C: USVI Whelk Survey Final Report




Figure 5. Relationship between size and abundance as observed for Cittarium pica in the
USVI. Average abundance (number per m2) is plotted against average shell width. Data
are from quadrat surveys. Results from linear regression are shown with r 2 values. A. St.
Croix. B. St. Thomas and St. John.



A. St. Croix y = -1.767x + 40.887
60 r2 = 0.4386



E

14U-

20 -





0
0 5 10 15 20
No. I m2



B. St. Thomas and St. John y = -0.4534x + 29.787
60 r2 =0.1652


*

40









0
oo- ---


20 -- - -




0 10 20 30 40
No. I m2







SEAMAP-C: USVI Whelk Survey Final Report


Figure 6. Differences in Cittarium pica populations between exposed and protected
sites. Data are from six different areas in the USVI where paired-site surveys were
conducted on the relatively exposed (windward) and relatively protected (leeward)
stretches of the same coastline (see text). Presented data are from quadrat surveys, error
bars represent standard deviation. A. Average abundance (number per m2). B. Average
size (shell width in mm).


40
Windward (exposed) A. Average Abundance

O Leeward (protected)
30



E
S20
6
z



10





Hughes Point Europa Bay Buck Island Whistling Cay Long Point Pull Point
St.Croix St.John St.Croix St.John St.Croix St.Croix



100
B. Average Size U Windward (exposed)

80 0 Leeward (protected)



E 60



40



20



0
Hughes Point Europa Bay Buck Island Whistling Cay Long Point Pull Point
St Crolx St John St Crolx St John St Crolx St Crolx







SEAMAP-C: USVI Whelk Survey Final Report




Figure 7. Accessibility of sites compared to reproductive attributes of Cittarium pica
populations. Data for abundance of harvest-size adults (> 62 mm shell width) are from
belt transects. Data for percentage of reproductively mature individuals are from quadrats
surveys done at the same sites, and assume that C. pica reaches reproductive maturity at
31 mm. Sites are classified as easy access (black circles), limited access (gray diamonds)
or restricted access (white circles). A. St. Croix. B. St. Thomas and St. John.


A. St. Croix
100% I


80%


* easy access
* limited access
O restricted access/harvest


40
No. Harvest-Size Adults/100 m2




B. St. Thomas and St. John


40 60
No. Harvest-Size Adults/100 m2


"o
> 60%


o 40%
C.


100%


80%
01


> 60%


O 40%
C.
ci


easy access
S* limited access

O restricted access/harvest






0 \

I


i':







SEAMAP-C: USVI Whelk Survey Final Report




Figure 8. Variation in the density of Cittarium young-of-the-year (YOY; < 5 mm shell
width) during 2003-2004 surveys at 41 areas in the USVI. Values are reported as the
average number of YOY per m2 observed during quadrat surveys. A. St. Croix (17 survey
areas). B. St. Thomas and St. John (24 survey areas). Note the different scales used for y-
axes.


A. St. Croix


1


0
o


I

*








B*o






B. St. Thomas and St. John


OSt. John
* St. Thomas


0


0 0
0-42----a ,


Cc o&~ ,~? K5


?N
B


0P
N
51


C,y"
N


,"* ,~""







SEAMAP-C: USVI Whelk Survey Final Report


Figure 9. Historic data for Cittarium pica size distribution compared to results obtained
in this study. Data from quadrats and belt transects were combined (see text) A. Henley
Cay, St. John. B. Cockroach Island, St. Thomas.





A. Henley Cay

0 40
35- - c.1981 (n = 222)
035

030 2004 (n = 58*)

>025

S020

015

010

005

0000 i "''' .




Shell Width (mm)


B. Cockroach Island


'9 ^ '9 ^ '9 N' 9 '9 '9'<(


Shell Width (mm)







SEAMAP-C: USVI Whelk Survey Final Report


Appendix 1. Cittarium pica survey results using the quadrat method.
No. Total Topshell Density (No./m2) Topshell Size (mm)
Site Name (code) Quads No. Avg StDev Max Min. Avg. StDev Max Min
St. Croix


Sprat Hall (SPH) 20
Hams Bay (HAM) 15
Barons Bluff (BRB) 15
Long Point, East (LPE) 15
Annaly Bay (ANB) 15
Knights Bay (KNB) 11
Grassy Point (GRP) 15
Grapetree Point (GTP) 13
Watch Ho (WHP) 10
East Point (EPT) 9
Buck Island-1 (BI-1) 15
Buck Island-2 (BI-2) 15
Hovensa (HOV) 8
Hughes Point-1 (HP-1) 11
Maroon Hole (MAH) 12
NW Tidepools (NTP) 9
Long Point, West-1 (LP-1) 8
Long Point, West-2 (LP-2) 8
Hughes Point-2 (HP-2) 12
Pull Point-1 (PP-1) 8
Pull Point-2 (PP-2) 8

St. Thomas
Rotto Cay (ROT) 17
Dog Island (DGI) 16
Secret Harbor (SEC) 8
Thatch Cay (THC) 12
Salt Cay (SLT) 15
Stumpy Bay (STB) 10
Water Island (WAT) 8
Hassel Island (HAS) 14
L. Hans Lollick (LHL) 10
Inner Brass (IBR) 10
Saba Island (SAB) 12
Lovango (LOV) 10
Cockroach Island (CRI) 13
Mandal (MAN) 9

St. John
Turner Bay (TUR) 13
Flanagan Island (FLA) 10
Reef Bay (RFB) 13
Round Bay (RND) 15
Europa Bay-1 (EU-1) 14
Henley Cay (HEN) 15
Waterlemon Cay (WLM) 16
Whistling Cay-1 (WST-1) 14
Whistling Cay-2 (WST-2) 11
America Point (AMP) 10
Rams Head (RAM) 15
Europa Bay-2 (EU-2) 10


70 3.5 5.2 19
65 4.3 4.7 20
118 7.9 4.9 18
201 13.4 7.7 25
143 9.5 6.0 25
175 15.9 8.6 28
55 3.7 4.9 15
29 2.2 4.1 15
95 9.5 6.6 20
7 0.8 1.3 4
41 2.7 4.9 15
77 5.1 7.3 24
12 1.5 2.5 6
28 2.5 3.8 13
53 4.4 3.5 14
119 13.2 10.1 33
90 11.3 7.6 25
156 19.5 17.7 58
110 9.2 10.2 27
97 12.1 7.2 24
139 17.4 14.5 45


72 4.2 5.4 16
18 1.1 1.8 6
261 32.6 18.1 68
29 2.4 2.4 7
72 4.8 7.2 20
55 5.5 4.8 15
242 30.3 26.2 71
119 8.5 10.2 27
120 12.0 11.2 34
52 5.2 8.3 25
84 7.0 8.6 20
113 11.3 10.3 27
53 4.1 5.6 21
358 39.8 33.9 93


91 7.0 5.9 19
63 6.3 13.8 45
157 12.1 14.5 45
92 6.1 10.3 42
24 1.7 2.1 7
51 3.4 5.3 15
152 9.5 11.2 47
52 3.7 8.1 29
121 11.0 8.1 25
109 10.9 6.1 19
122 8.1 6.2 18
160 16.0 13.4 33


0 16.6 6.1 41
0 23.2 8.4 37
0 20.8 14.1 59
1 16.2 8.8 78
2 20.2 9.2 56
0 19.0 4.8 48
0 39.9 23.8 105
0 32.7 13.5 60
0 20.7 7.5 41
0 34.9 14.1 64
0 36.4 8.6 57
0 33.2 17.2 92
0 69.0 13.6 93
0 58.8 20.8 78
1 19.0 12.2 55
2 26.5 11.7 80
4 20.5 7.5 37
1 12.5 8.0 29
0 13.5 13.4 55
6 13.9 9.2 57
0 11.4 4.1 22


0 45.3 15.5 97
0 54.1 21.3 85
9 16.2 6.9 57
0 25 13.2 47
0 30.5 15.9 64
0 11.9 6.6 29
5 20 6.3 57
0 23.2 6.5 58
0 11.2 4.6 36
0 14.3 11.3 58
0 36.1 12.8 64
0 28.8 10.6 56
0 27.2 19.8 58
0 18.3 11.9 55


0 19.0 5.9 41
0 29.9 11.0 62
0 17.9 9.5 42
0 23.3 5.1 34
0 38.8 12.1 57
0 25.5 16.6 52
0 34.5 15.5 60
0 34.9 11.7 58
0 12.0 9.6 51
0 13.4 8.8 51
0 17.8 15.7 52
0 25.4 8.9 52







SEAMAP-C: USVI Whelk Survey Final Report


Appendix 2. Cittarium pica survey results using the belt transect method.
No. Total No. Avg Density (No./m2) Size (mm)
Site Name (code) Belts All (>62) (<62) All (>62) Avg StDev Max Min
St. Croix


Sprat Hall (SPH) 2
Hams Bay (HAM) 2
Long Point, East (LPE) 2
Annaly Bay (ANB) 2
Knights Bay (KNB) 2
Grassy Point (GRP) 2
Grapetree Point (GTP) 2
Watch Ho (WHP) 2
East Point (EPT) 2
Buck Island-1 (BI-1) 2
Buck Island-2 (BI-2) 2
Hovensa (HOV) 2
Hughes Point-1 (HP-1) 2
Maroon Hole (MAH) 2
Long Point, W-1 (LP-1) 1
Long Point, W-2 (LP-2) 1
Hughes Point-2 (HP-2) 2
Pull Point-1 (PP-1) 1
Pull Point-2 (PP-2) 1

St. Thomas
Rotto Cay (ROT) 2
Dog Island (DGI) 2
Secret Harbor (SEC) 2
Thatch Cay (THC) 2
Salt Cay (SLT) 2
Stumpy Bay (STB) 2
Water Island (WAT) 2
Hassel Island (HAS) 2
L. Hans Lollick (LHL) 2
Inner Brass (IBR) 2
Saba Island (SAB) 2
Lovango (LOV) 2
Cockroach Island (CRI) 2
Mandal (MAN) 2

St. John
Turner Bay (TUR) 2
Flanagan Island (FLA) 2
Reef Bay (RFB) 2
Round Bay (RND) 2
Europa Bay-1 (EU-1) 2
Henley Cay (HEN) 2
Waterlemon Cay (WLM) 2
Whistling-1 (WST-1) 2
Whistling-2 (WST-2) 2
America Point (AMP) 2
Rams Head (RAM) 2
Europa Bay-2 (EU-2) 2


0.01
0.00
0.08
0.10
0.00
0.18
0.08
0.05
0.27
0.22
0.34
0.74
0.45
0.00
0.00
0.00
0.01
0.02
0.02


0.38
0.41
0.01
0.15
0.20
0.00
0.17
0.12
0.02
0.32
0.14
0.26
0.39
0.00


0.01
0.92
0.00
0.00
0.05
0.08
0.34
0.10
0.00
0.01
0.34
0.05


72

70.1 4.9
69.0 10.1

99.2 10.4
72.3 15.4
101.4 11.6
80.7 13.3
95.0 7.1
93.6 6.2
86.0 10.6
74.1 8.1



84.0
56.0
83.0


6.7
9.6

12.1
14.9

17.2
17.8
12.7
11.3
6.3
13.8
8.7


76
10.3 109


13.2 86
14.3 90
11.1 94
13.5 105

98
10.5 87
10.5 85


Note: Belt transect surveys were not conducted at Barons Bluff (BRB) and Northshore tidepools (NTP).









SEAMAP-C: USVI Whelk Survey Final Report





Appendix 3. Size distribution of Cittariumpica at St. Croix sampling sites as determined from

quadrat sampling (columns) and belt transect sampling (lines).

Sprat Hall
20 r02


MQuadrats (n = 70)
Belt Transects (n = 1)


















Shell Width (mm)




Hams Bay


Co
S10
E

















20








a

E


6





00-


Barons Bluff


SQuadrats (n =118)

30



20



10



00


Shell Width (mm)


M Quadrats (n = 65)
Belt Transects (n = 0)


















Shell Width (mm)


01
a





















o2
I-
01


E




























6
z



0








02




a

I-

01 |

E


z



0









SEAMAP-C: USVI Whelk Survey Final Report





Appendix 3 continued. Size distribution of Cittarium pica at St. Croix sampling sites as

determined from quadrat sampling (columns) and belt transect sampling (lines).


Long Point, East


M Quadrats (n = 201)
- Belt Transects (n = 8)


60 +


20


Shell Width (mm)


Annaly Bay


M Quadrats (n= 143)
--Belt Transects (n = 10)


Shell Width (mm)


Knights Bay


M Quadrats (n = 175)
- Belt Transects (n = 0)


Shell Width (mm)


08




06 ?


1-

04 |

E

02
z



o














I--
















6
Z



0
a1


















a




6
02 Z



0
0


004






40





a


'20
E

6
z




oo00






100


80



60



40



20









SEAMAP-C: USVI Whelk Survey Final Report





Appendix 3 continued. Size distribution of Cittarium pica at St. Croix sampling sites as

determined from quadrat sampling (columns) and belt transect sampling (lines).


Grassy Point


SQuadrats (n= 55)
-- Belt Transects (n = 18)


20








lo
a
-S
S10
E

o
6
z




00

















-o
20








Co
a
'10
E


6
z




00







40









'20
E


6
z




00


M Quadrats (n = 29)
- Belt Transects (n = 8)


Shell Width (mm)


Watch Ho


SQuadrats (n= 95)
- Belt Transects (n = 5)


Shell Width (mm)


Shell Width (mm)



Grapetree Point


02







I-

01

E


6
z



0















1--








t4




I-
01 o

E


6
z



0







04




03 ?
a
I

02

E

C.
01 6
z



00


---


m


o o








SEAMAP-C: USVI Whelk Survey Final Report




Appendix 3 continued. Size distribution of Cittarium pica at St. Croix sampling sites as
determined from quadrat sampling (columns) and belt transect sampling (lines).


East Point


20





PS
S10
E

6




00







40







Cr
E20
E

6
z



00


-U-


Shell Width (mm)


Hovensa


M Quadrats (n = 12)
-Belt Transects (n = 74)















Shell Width (mm)


M Quadrats (n = 7)
--Belt Transects (n = 27)


U-.


Shell Width (mm)




Buck Island-1

SQuadrats (n= 41)
--Belt Transects (n = 22)


30


10+


04



03
c
I-
02

E

01 6
z


00


02





I-

01

E

6
z


0







04






I-
02

E


z


0


A









SEAMAP-C: USVI Whelk Survey Final Report





Appendix 3 continued. Size distribution of Cittarium pica at St. Croix sampling sites as

determined from quadrat sampling (columns) and belt transect sampling (lines).



Hughes Point-1


M Quadrats (n = 28)
Belt Transects (n = 45)


















Shell Width (mm)



Maroon Hole


220

a

E

C10
z
6





00







20







Co
a
S10
E


6
z


Shell Width (mm)



NW Tidepool


SQuadrats (n= 119)


Shell Width (mm)


M Quadrats (n = 53)
- Belt Transects (n = 0)


03





02 c

I-
ca

E
01 1

6
z



0







02




a
CS
I-






6
0
Q.




o


30





S20



E

a 10
z



00









SEAMAP-C: USVI Whelk Survey Final Report




Appendix 3 continued. Size distribution of Cittarium pica at St. Croix sampling sites as

determined from quadrat sampling (columns) and belt transect sampling (lines).


Long Point, West-1


M Quadrats (n = 90)
- Belt Transects (n = 0)


Shell Width (mm)


Pull Point-1


I Quadrats (n = 97)
- Belt Transects (n = 1)


60 +


20


00






80



60



Co
a
'40
E

6
Z 20




00


08



06 ?

1-










06







02 6
z
o

I--













04

E

02 6
z


Shell Width (mm)









SEAMAP-C: USVI Whelk Survey Final Report





Appendix 4. Size distribution of Cittariumpica at St. Thomas sampling sites as determined from

quadrat sampling (columns) and belt transect sampling (lines).


Rotto Cay


20






a

S10
E
o.
6
z




00






20







ro
S10
E

6
z




oo


Dog Island


Shell Width (mm)


Secret Harbor


MQuadrats(n= 261)
--Belt Transects (n = 1)


Shell Width (mm)


02







1--
t01

0o
E


6
z






o0



-0
01







a,
a.


























6
z



















06






02 Z
I





































0


100


80


60


40


20


Shell Width (mm)









SEAMAP-C: USVI Whelk Survey Final Report





Appendix 4 continued. Size distribution of Cittarium pica at St. Thomas sampling sites as

determined from quadrat sampling (columns) and belt transect sampling (lines).



Thatch Cay


M Quadrats (n= 29)
--Belt Transects (n = 15)


20








a
10
E


z




00


Salt Cay


M Quadrats (n = 72)
Belt Transects (n = 20)


















Shell Width (mm)


Stumpy Bay


M Quadrats (n = 55)
- Belt Transects (n = 0)


Shell Width (mm)


Shell Width (mm)


02





a0
C
I-

01

E


6
z


20





a



S10
E
o.
6





00


02






I-

01

E


6
z



0











03 ?

I-

02

E

01 6
z



0


~888888~~









SEAMAP-C: USVI Whelk Survey Final Report





Appendix 4 continued. Size distribution of Cittarium pica at St. Thomas sampling sites as

determined from quadrat sampling (columns) and belt transect sampling (lines).


Water Island


M Quadrats (n = 242)
- Belt Transects (n = 17)


M Quadrats(n=119)
--Belt Transects (n = 12)


Shell Width (mm)


Little Hans Lollick


SQuadrats (n = 120)
- Belt Transects (n = 2)


160



120



80



40


00I-
CD


1



08



06



04 E


6
02 Z



0


Shell Width (mm)


Hassel Island


30+


10+


00







60






40



E

20



z

oo


04




03 ?




02

E


01 6
z



0
o




















02
06

z



0


Shell Width (mm)









SEAMAP-C: USVI Whelk Survey Final Report





Appendix 4 continued. Size distribution of Cittarium pica at St. Thomas sampling sites as

determined from quadrat sampling (columns) and belt transect sampling (lines).



Inner Brass


40




-30




' 20
E

6
Z10




00






20






Co
a
S10
E


6
z




00


Saba Island


SQuadrats (n= 84)
--Belt Transects (n = 14)


Shell Width (mm)


M Quadrats(n= 113)
--Belt Transects (n = 26)


Shell Width (mm)


04




03 ?




02

E
C





0
















016




z
0




a





E






0


Lovango Cay


30


10


04




03 ?

1-

02

E






0


Shell Width (mm)









SEAMAP-C: USVI Whelk Survey Final Report





Appendix 4 continued. Size distribution of Cittarium pica at St. Thomas sampling sites as

determined from quadrat sampling (columns) and belt transect sampling (lines).


Cockroach Island


SQuadrats (n= 53)
Belt Transects (n = 39)


















Shell Width (mm)


Mandal


M Quadrats (n = 358)
--Belt Transects (n = 0)


S60
a
E
40

6
z
Z
20



00


Shell Width (mm)


-30
to


a
' 20
E


6
Z n


04




03 ?

1-
02


















08
C
















I-0 6
02



0.
o

















04
o06





a


02 d
z



0









SEAMAP-C: USVI Whelk Survey Final Report





Appendix 5. Size distribution of Cittariumpica at St. John sampling sites as determined from

quadrat sampling (columns) and belt transect sampling (lines).


M Quadrats (n = 91)
- Belt Transects (n = 1)


Flanagan Island


H Quadrats (n = 63)
--Belt Transects (n = 92)


Shell Width (mm)


Reef Bay


M Quadrats (n = 157)
- Belt Transects (n = 0)


Shell Width (mm)


Turner Bay


06




a
04 =
I-



E
02

6




0


Shell Width (mm)


40







Co

720



6
z




00









40




030


2o
a
'20
E


6
S10




00


04




03 ?


I--

02

E


01




0









04




03 1
a,

I-






01 6
z



0


lO 8 O O


A









SEAMAP-C: USVI Whelk Survey Final Report





Appendix 5 continued. Size distribution of Cittarium pica at St. John sampling sites as

determined from quadrat sampling (columns) and belt transect sampling (lines).


Round Bay


SQuadrats (n =92)
- Belt Transects (n = 0)


Shell Width (mm)




Europa Bay-1

M Quadrats (n = 24)
Belt Transects (n = 8)


















Shell Width (mm)





Henley Cay


00








20







to

' 10
E


6
z




00








20












0o
a




z




00-


Shell Width (mm)


30


10


M Quadrats (n = 51)
- Belt Transects (n = 8)


04




03 ?



02

E

01 6
z



0








02




a
to



0a


















I-
01
E






























6
z



0








02







I-
01





z



0









SEAMAP-C: USVI Whelk Survey Final Report





Appendix 5 continued. Size distribution of Cittarium pica at St. John sampling sites as

determined from quadrat sampling (columns) and belt transect sampling (lines).


Waterlemon Cay


04




03 ?
a,
1-

02

E

01 6
z


Shell Width (mm)


Whistling Cay-1


SQuadrats (n= 52)
--Belt Transects (n = 10)


30


10+


Shell Width (mm)




America Point


I Quadrats (n = 109)
- Belt Transects (n = 1)


04




03 ?


01
02



0.
01 6
z












04




03 ?
a
I--

02




01 6
z



0


a"

ro
20



z10




00


Shell Width (mm)








SEAMAP-C: USVI Whelk Survey Final Report




Appendix 5 continued. Size distribution of Cittarium pica at St. John sampling sites as
determined from quadrat sampling (columns) and belt transect sampling (lines).


Ram Head


M Quadrats (n= 122)
--Belt Transects (n = 34)


40



-30



J20


o
E

6
S10-



00


04







02

E

1 o



0


Shell Width (mm)


'I ZJ \


888888~~








SEAMAP-C: USVI Whelk Survey Final Report




Appendix 6A. Size distribution of Cittarium pica at windward (exposed) and leeward (protected)

paired-sample sites at Hughes Point, St. Croix. Data are from quadrat sampling (columns) and belt

transect sampling (lines).


40






E
S20

6





00


W20
0

z


Hughes Point, Leeward M Quadrats (n= 110)
Belt Transects (n = 1)


Shell LO LWdth ( Lmm)
A N D (N N COD CO o o [,) 0) 0 0 M
Shell Width (mm)


02
to
-,





01
C
I--

m
01 E


d



0




02
t;
c,
C


m
01 E


d




0








SEAMAP-C: USVI Whelk Survey Final Report


Appendix 6B. Size distribution of Cittarium pica at windward (exposed) and leeward (protected)
paired-sample sites at Europa Bay, St. John. Data are from quadrat sampling (columns) and belt
transect sampling (lines).


Europa Bay,
Windward


60 -


"40

E
w
C.






00


M Quadrats (n= 24)
--Belt Transects (n = 8)


Europa Bay,
Leeward


I Quadrats (n= 160)
--Belt Transects (n = 5)


LO C LO O LD O LD O LD O CO LD O LD O LD O LD O L) S
A N- N- ( m ( m C LO LO (D (D [_ [_ O O G) G)
Shell Width (mm)


02









6
,-












0
I-


2




00


02



I-



01 E


z


0


_ Ch ~I\~







SEAMAP-C: USVI Whelk Survey Final Report



Appendix 6C. Size distribution of Cittarium pica at windward (exposed) and leeward (protected)
paired-sample sites at Buck Island, St. Croix. Data are from quadrat sampling (columns) and belt
transect sampling (lines).




Buck Island, MQuadrats (n= 41)
20 Windward -Belt Transects (n = 22)

20 02



C
o 6





Buck Island, MQuadrats (n= 77)
2 0 Leeward --Belt Transects (n = 34) 0







00 I






Shell Width (mm) B








SEAMAP-C: USVI Whelk Survey Final Report




Appendix 6D. Size distribution of Cittarium pica at windward (exposed) and leeward (protected)
paired-sample sites at Whistling Cay, St. John. Data are from quadrat sampling (columns) and belt
transect sampling (lines).


Whistling Cay,
Windward


Whistling Cay,
Leeward


M Quadrats (n = 52)
- Belt Transects (n = 10)


MQuadrats (n = 121)
--Belt Transects (n = 0)


SN (N C Shell Width ( mm) 0
Shell Width (mm)


40



S30
30
a

E 20


d
z
10


00 -


40



S30

a

E 20
0.

z
10



00


02

I,-




01 E

01
6
z



0



02

U

I-



01 E


d
z



0








SEAMAP-C: USVI Whelk Survey Final Report


Appendix 6E. Size distribution of Cittarium pica at windward (exposed) and leeward (protected)
paired-sample sites at Long Point-West, St. Croix. Data are from quadrat sampling (columns) and
belt transect sampling (lines).



1 08


Long Point-West,
Windward


Long Point-West,
Leeward


M Quadrats (n = 90)
- Belt Transects (n = 0)


MQuadrats (n = 156)
- Belt Transects (n = 0)


S CO LOShell Width ( CO mm) )
Shell Width (mm) A


-40



00





-o
C 20




00-


60




O40

E
w
C.
0 20 0


06 fl


I--

04

E

02 6
z



0
Ub



06 t


I-
04

E

02 d
z


ft=








SEAMAP-C: USVI Whelk Survey Final Report


Appendix 6F. Size distribution of Cittarium pica at windward (exposed) and leeward (protected)
paired-sample sites at Pull Point, St. Croix. Data are from quadrat sampling (columns) and belt
transect sampling (lines).


M Quadrats (n = 97)
- Belt Transects (n = 1)


MQuadrats (n = 139)
- Belt Transects (n = 1)


Pull Point,
Windward


60




O40










00
E




00-


60




-40




,
E
0.
0 20 0


04



I--




02

C
z
















2
0



U


I





z



0


Pull Point,
Leeward


SN N CO COShell Width ( mm) 0
Shell Width (mm) A


I




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