This report addresses stock assessment and monitoring, larval
surveys, stock restoration, reproductive failure in nearshore
conch, and additonal information and statistics.
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Queen Conch
Restoration
Robert Glazer
Associate Research Scientist
Florida Marine Research Institute
South Florida Regional Laboratory
Marathon, Florida
INTRODUCTION
Queen conch are found predominantly in south Florida, from the
Florida Keys to Key Biscayne. They once constituted significant
commercial and recreational fisheries in Florida, however, in 1975,
the commercial fishery was closed due to overfishing. This ban was
extended to the recreational fishery in 1985 in state waters
(Florida Administrative Code, Chapter 68b-16.003 http://fac.dos.state.fl.us/) and 1986 in
contiguous federal waters for those aboard vessels registered in
Florida (Florida Administrative Code, Chapter 68b-16.005). In 1986,
the State of Florida began a research program designed to monitor
the recovery of the conch stock and to determine how best to
rehabilitate the depleted population. The queen conch program has
taken a "community-based" approach; most of the laboratory and
field studies were conducted under partnerships involving the
State, the U.S. Fish and Wildlife Service, The Nature Conservancy,
and an extensive base of community volunteers.
RESEARCH RESULTS
Stock Assessment/Monitoring
In 1986, the State began a program to
monitor the recovery of the conch stock after the closure. From
1987 through 1993, we conducted surveys using towed-divers. These
surveys showed that the population was not recovering on its own
(Glazer and Berg, 1994; Berg and Glazer, 1995).
In 1992, we began to shift our focus towards the conch spawning
stock and stock restoration. The spawning stock surveys were
conducted using belt-transects at all spawning aggregations located
on the reef tract. These surveys examined up to 27 aggregations
from Key Largo to Key West on a yearly basis. The surveys
determined densities (conch per m 2) within the aggregations and
the area encompassed by each aggregation. The number of conch in
each aggregation was estimated by multiplying these two
parameters.
Through 1997, we observed an overall increase in the number of
adult conch within the aggregations (Figure 1). The minimum number
of adult conch we observed was approximately 5,750 in 1992, and the
maximum was 20,650 in 1997. In 2000, we estimated that there were
approximately 18,200 adult conch within spawning aggregations in
south Florida. We also observed an increase in the area encompassed
by the aggregations.
Larval Surveys
Conch recovery in south Florida has been slower than we
anticipated after the closure of the fishery. Since recovery is
dependant on the supply of larvae, we initiated a series of studies
designed to determine the origin of conch larvae supplying south
Florida's conch population. In 1990, we conducted experiments that
demonstrated that the conch population in south Florida was not
isolated from other populations in the Caribbean and that there was
a component of the Florida conch population that originated
elsewhere (Campton et al., 1992). The next step was to determine
the extent of the contribution to the south Florida conch
population from upstream sources in the Caribbean region (e.g.,
Mexico, Cuba, Belize). In 1996, we began a study to examine the
extent of the contribution from larvae recruiting to south Florida.
(Hawtoff et al., 1998). The results from this study showed that few
larvae were entering the Florida Keys and that the contribution
from Caribbean sources was minimal. Thus, we determined that
increasing the local spawning stock should result in increased
larval availability.
Two additional studies supported this conclusion. In 1992, we
conducted a study in conjunction with a NOAA partner, the Caribbean
Marine Research Center, to determine the larval supply to Looe Key
in the Florida Keys and to compare it with a population in the
Bahamas where conch are abundant. This study demonstrated that
larval conch abundance in Florida was an order of magnitude lower
than in the Bahamas (Stoner et al. 1996). In 1997, we repeated our
surveys at Looe Key. In this study, we demonstrated that the larvae
were an order of magnitude more abundant than in the previous
survey (Hawtoff et al., in press). The increase in larval abundance
occurred simultaneously to the increase in the spawning stock
(Figure 1). This led further support to our conclusions which
suggested that the local spawning population is a critical source
of larvae supplying south Florida.
Thus, based on our surveys of the spawning stock and on our
larval surveys, we believe that the slow rate of recovery of the
Florida conch population is due mainly to limited larval
availability. We also believe that the recovery of the local conch
stock will not occur rapidly until the local spawning stock
increases substantially beyond the current levels and that further
enhancement of the spawning stock is critical to rehabilitating the
south Florida conch population.
Stock Restoration
We conducted a series of field and laboratory experiments with the
goal of evaluating the efficacy of using hatchery-reared juvenile
conch to supplement the wild spawning stock. Specifically, we
examined the variables that limit post-release survival and
examined how to maximize that survival. All animals used in the
experiments were produced at our research-scale conch hatchery on
Long Key in the Florida Keys. Table 1 presents the variables that
were examined and the results from those experiments. Based on the
results of the experiments, we determined that we should release
10-cm (approximately 4 inches) conch in the fall on upcoming full
moons. Additionally we determined that the release site should be
distant from areas of high predator density. We determined that
exposing a hatchery-reared conch to a caged predator prior to
release resulted in development of optimal behavioral and
morphological characteristics that will result in significantly
greater survival than those conch that are not exposed. After these
experiments were complete, we coupled the cost of seed production
with post-release survival to determine the cost per 15-cm
(approximately 6 inches) survivor. We determined that a 10-cm conch
released in the fall on upcoming full moons and surviving to 15-cm
costs approximately $9.00 per individual.
ISSUES
Issue 1. Reproductive Failure in Nearshore
Conchark
Conch in the Florida Keys are distributed within two disparate
zones (Figure 2). In the offshore zone, conch are found in discrete
aggregations in coral rubble and sand environments in the back
reef. In the nearshore zone, conch are located in the hardbottom
community adjacent to the shoreline. Conch distribution within the
nearshore zone is, for the most part, widespread. Juvenile and
adult conch do not migrate between the two zones because the silt
which characterizes the bottom of Hawk Channel is poor habitat for
conch and effectively serves as a barrier (Berg and Glazer, 1995).
Therefore, conch that are transported as larvae from the offshore
zone and settle in the nearshore zone remain there.
Despite extensive surveys, we never observed conch
reproducing or spawning in nearshore aggregations; all spawning was
observed offshore (Glazer and Quintero, 1998). However, we have
received several anecdotal reports indicating that conch once
reproduced nearshore. In 1998, we conducted a study to compare
conch reproductive behavior and gonadal development between the two
zones (McCarthy et al., 2000). Our studies showed that conch in the
offshore zone developed normal gonads whereas those located
nearshore had distinct gonadal deficits and were unable to
reproduce (Figure 3). Our study also examined the reproductive
development of conch transplanted between the two zones. The
results indicated that conch transplanted from the nearshore zone
to the offshore zone developed fully functional gonads. Conversely,
those conch transplanted from offshore to nearshore showed rapid
loss of gonadal tissue.
Issue 2. Chronic Effects of Poor Water Quality on Larval
Fitness
The queen conch hatchery on Long Key was designed and constructed
in 1991. When hatchery production was initiated, we quickly
realized that the maximum larval density we could achieve was one
larva per 2 liters of seawater. Additionally, the time to
metamorphosis in our cultures was approximately 45 days. This
contrasted with conditions at a commercial conch hatchery in the
Turks and Caicos where they reported densities of 20 conch per
liter and time to metamorphosis of approximately 20 days. After
careful analysis, we implemented an ozone system for the treatment
of incoming water. Ozone, when applied to seawater, removes
dissolved organic materials. By adding ozone, we effectively made
the nearshore waters more closely resemble the water associated
with "reef" conditions. When the ozone system became functional, we
were able to culture conch larvae at densities approaching 10
larvae per liter and the time to metamorphosis dropped from
approximately 45 days to approximately 20 days. Since dissolved
organic materials may result from eutrophication, the results from
this study suggest that declining water quality associated with
nutrification may reduce the overall fitness of larval conch. This
observation has widespread implications for the effects of
nearshore coastal development on Florida's conch stock.
FUTURE DIRECTION
Monitoring and Larval Surveys
We will continue to monitor the spawning stock in order to assess
the recovery of the population. We will also expand the monitoring
program to include nearshore populations. We intend to continue
limited larval surveys to facilitate the evaluation of the impacts
of our restoration efforts.
Restoration Research
Beginning in the spring of 2001, we began implementing a
restoration program based on a two-part approach:
- We began transplanting conch as a method to increase the
spawning stock. Juvenile and adult conch are transplanted from
nearshore, non-spawning areas to offshore spawning aggregations. We
are receiving assistance in this effort from The Nature Conservancy
and our large base of community volunteers.
We prefer this strategy to ramping-up hatchery production because
it is far less costly (Glazer and Delgado, 1999). Additionally, the
conch that are used to enhance the population are wild and,
therefore, have genetic, morphological and behavioral advantages
over hatchery conch (Stoner and Glazer, 1998). Additionally, a
transplantation program fosters community involvement in the
management of this resource. Since this project began in May 2001,
we have transplanted 920 adult and late-stage juvenile conch. This
is equivalent to releasing at least 10,000 hatchery-raised
juveniles based on the expected mortality after release.
- Hatchery conch will be produced for release by our private
partners. We have developed strong public-private partnerships
with two not-for-profit organizations (Keys Marine Conservancy and
the Conch Research and Education Foundation) who have specific
charters to produce conch for a queen conch restoration program. We
have and will continue to provide technical assistance for the
culture of hatchery-reared conch and will define the protocols for
release. Conch produced by these organizations will be released
only under the guidance and supervision of the FMRI at no cost to
the state. These releases will augment our transplantation
efforts.
The effectiveness of these programs will be evaluated by
monitoring spawning aggregations for density, area encompassed by
the aggregations, and abundance of conch. We also intend to
continue monitoring larval supply as a mechanism for evaluating the
success of these initiatives. We will examine differences in
resource utilization and reproductive behavior between native conch
and their transplanted and hatchery-reared counterparts.
Additionally, we will examine the effects transplanting has on the
habitat from which, and into which, they are transplanted.
LITERATURE CITED
Berg, C. J., Jr., and R. A. Glazer. 1995. Stock assessment of a
large marine gastropod (Strombus gigas) using
randomized and stratified towed-diver censusing. - Rapp, P.-v.
Réun. Cons. int. Explor. Mer, 199:247-258.
Campton, D. E., L. Robison, C. J. Berg, Jr, and R. A. Glazer.
1992. Genetic patchiness among populations of queen conch
Strombus gigas in the Florida Keys and Bimini. Fish.
Bull., 90:250-259.
Delgado, G., R. A. Glazer, N. J. Stewart, K. J. McCarthy, and J.
A. Kidney. 2000. Modification of behavioral and morphological
abnormalities in hatchery-reared queen conch: implications for a
stock enhancement program (Strombus gigas, L.). Proc.
Gulf Caribb. Fish. Inst. 51:80-86.
Delgado, G., R. A. Glazer, N. J. Stewart, K. J. McCarthy, and J.
A. Kidney. In Prep. Predator Induced Behavioural and Morphological
Plasticity in the Tropical Marine Gastropod, Strombus
gigas L.
Glazer, R. A. and C. J. Berg, Jr. 1994. Queen conch research in
Florida: an overview. In: R. S. Appeldoorn (ed.) pp. 79-95. Proc.
1st Latin American Malacological Conference. Special Workshop on
the Management and Culture of Queen Conch.
Glazer, R. A. and G. Delgado. 1999. Optimizing Size at Release of
Hatchery-Raised Queen Conch Outplants: A Cost-Benefit Approach.
U.S. Fish and Wildlife Service Project P-1. 57 p.
Glazer, R. A. and R. Jones. 1997. Temporal factors influencing
survival of queen conch outplants. Final Report. U.S. Fish and
Wildlife Service Project P-1. 58 p.
Glazer, R. A. and I. Quintero. 1998. Observations on the
sensitivity of queen conch to water quality: implications for
coastal development. Proc. Gulf Caribb. Fish. Inst. 50:78-93.
Hawtoff, D. B., K. J. McCarthy, and R. A. Glazer. 1998.
Distribution and abundance of queen conch, Strombus gigas, in the
Florida Current: implications for recruitment to the Florida Keys.
Proc. Gulf Caribb. Fish. Inst. 50:94-103.
Hawtoff, D. B., R. A. Glazer, and K. J. McCarthy. In press.
Spatial and temporal distribution of queen conch larvae in the
offshore waters of the Florida Keys. Proc. Gulf Caribb. Fish. Inst.
52.
McCarthy, K. J., C. T. Bartels, M.C. Darcy, J. R. Styer and R. A.
Glazer. 2000. Habitat induced reproductive failure of queen conch,
Strombus gigas, in the Florida Keys. U.S. Fish and Wildlife Service
Project P-1. 24 p.
Stoner, A. W., R. A. Glazer and P. J. Barile. 1996. Larval supply
to queen conch nurseries: relationships with recruitment process
and population size. Jour. Shellfish Res.15: 407-420.
Stoner, A. W. and R. A. Glazer. 1998. Variation in natural
mortality: implications for queen conch marine stock enhancement.
Bull. Mar. Sci. 62: 427-442.
Prior to July 1, 2004, the Fish and Wildlife Research
Institute was known as the Florida Marine Research Institute. The
institute name has not been changed in historical articles and
articles that directly reference work done by the Florida Marine
Research Institute.
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