This assessment provides an update on Florida's stone crab
fishery
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Executive
Summary
The stone crab fishery is unique in that fishers do not harvest
the crabs; rather, the fishers remove legal-sized claws from the
animals and then return the crabs alive to the water. Most female
crabs have already spawned one or more seasons by the time their
claws reach legal size.
The stone crab fishery is managed with a seven-month fishing
season (October 15 through May 15), a claw (propodus) minimum
harvest size of 2-3/4 inches (70 mm), trap specifications, and a
passive trap limitation program.
An average of 34% of the claws (weighted by regional landings)
observed by Florida Fish and Wildlife Conservation Commission (FWC)
samplers in fish houses statewide showed evidence of forced breaks.
Approximately 13% of the claws were regenerated claws, or claws
that grew back, providing evidence that some declawed crabs survive
the loss of their claws.
Historical landings, in pounds of claws on a calendar-year
basis, were extended back to 1902 to provide a context for
evaluating the more recent landings for which we have information
on effort. Landings generally increased until 1998.
This update includes commercial landings through the 2004-05
fishing season because the information from the 2005-06 season is
not yet available. Landings, in pounds of claws on a fishing-season
basis, have varied without trend since 1989-90. Peak landings were
3.5 million pounds statewide in the 1997-98 fishing season.
Statewide landings for 2004-05 were 3.0 million lb of claws.
The landings in October are good predictors of the landings for
the entire season. However, the October 2005 landings are not
expected to be a good indicator of the 2005-06 fishing season
landings due the effects of Hurricane Wilma, which reached the
Florida Keys on October 24 ,2005. Both the number of trips and the
pounds of claws landed in October 2005 were 56% of the 1985-2004
October averages.
Since the 1962-63 fishing season (the first year with an
estimate of the number of traps in the fishery), the number of
traps in the fishery has increased more than a hundred-fold -- from
15,000 traps in the 1962-63 season to 1.6 million traps in the
2001-02 season. In a physical count of traps conducted in the
1998-99 fishing season, FWC employees found 1.4 million traps,
which was twice the number that was estimated in 1992-93. As a
response to the rapidly increasing number of traps in the fishery,
the legislature in 2000 approved the stone crab trap limitation
program, which was implemented in October 2002. The number of
commercial trips also increased from 19,000 in the 1985-86 season
(the first season with trip information available) to a maximum of
38,000 trips in the 1996-97 season and then declined
afterwards.
Catch-per-trap has fluctuated widely, but it has shown a
generally decreasing trend over time. Catch rates dropped rapidly
from more than 20 pounds per trap in the 1960s to less than 10
pounds per trap by 1971 to less than five pounds per trap by 1983.
Catch rates continued to decline as the number of traps increased.
The catch-per-trap since 1983 has been so low that it declined only
slightly with the further doubling of traps. Catch-per-trip was
standardized using a generalized linear model to remove confounding
effects such as differences in location or time of the year. Most
of the stone crab landings come from Florida's gulf coast and the
Florida Keys. As would be expected in a fishery with a closed
season, the stone crab fishery has a strong pattern of declining
catch-per-trip during each season. The catch-per-trip data,
available only since the 1985-86 season, also showed that the
catch-per-trip has been declining over the same time period.
We used two models to evaluate the condition of the stock.
First, we used the landings, in pounds of claws, and the estimated
numbers of traps in the fishery from the 1962-63 through 2004-05
fishing seasons in a surplus production model. As expected, the
fishing mortality rate compared to its benchmark was too high.
Because of the nature of this fishery, biomass of claws is not
directly relevant. Second, in a modified DeLury model, we used the
monthly landings, expressed as numbers of claws, and the commercial
trips from the 1985-86 through 2004-05 fishing seasons to estimate
the October recruitment that would be necessary to account for
harvest and natural mortality (the DeLury continuity model). We
found that recruitment has varied without trend during this
period.
The status of the stock is best indicated by the stable landings
after 1989-90. The three-fold increase in the number of traps since
then suggests that the current level of landings is all that can be
harvested under current environmental conditions, regulations, and
fishery practices and that the fishery is overfishing. Recruitment
does not show any decline over the time series. These conclusions
were the same as those from the 1997 and 2001 assessments. The
stone crab fishery may be resilient because most female stone crabs
spawn one or more times before their claws reach legal size,
because some crabs survive declawing, and because the fishing
season is closed during the principal spawning season. However, the
fishery continues to have too many traps in the water. Further
evidence of excess traps is the low catch-per-trap level over a
very wide range of numbers of traps.
In earlier assessments, we concentrated only on the harvested
claws; but in this assessment, we began to investigate the
biological basis of the fishery, i.e., the number of crabs affected
by the fishery. There is no direct measure of this number.
Therefore, we used the average weight of claws in the commercial
claw-size categories to estimate the number of claws harvested and
the monthly estimates of the average number of legal-sized claws
per crab from a fishery-independent trapping study in Tampa Bay to
estimate the number of crabs with legal-sized claws.
Fishery-independent sampling has been conducted in the Tampa Bay
region since 1988. To add some credence to applying information
from Tampa Bay to the entire gulf coast of Florida, we compared the
claws per crab from Tampa Bay from February through May 2005 with
those from the Florida Keys (the only other area and time with
comparable information). There was no significant difference
between the number of claws per crab (1.21 claws per crab in the
Keys and 1.23 claws per crab in Tampa Bay).
For the past decade (1995-96 to 2004-05 fishing seasons), the
gulf coast fishers have declawed approximately 10.5 million crabs
during each seven-month fishing season.
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