This article is the June 2007 Report to the Florida Fish and
Wildlife Commission Division of Marine Fisheries Management: a
summary on the life history and ecology of blue crab, especially
information about Florida's blue crab populations.
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A stock assessment for blue
crab, Callinectes sapidus, in Florida waters
Michael D. Murphy, Anne L. McMillen-Jackson, and Behzad
Florida Fish and Wildlife Conservation Commission
Florida Marine Research Institute - St. Petersburg, Florida
Report to the Florida Fish and Wildlife Commission Division of
In this second quantitative assessment for blue crabs in Florida
we provide separate, detailed population analyses for blue crabs
inhabiting waters along the gulf and Atlantic coasts. Although we
treat these populations as separate, there may be a relatively high
movement of blue crab from the gulf to the Atlantic population.
Updated information is provided on key aspects of their life
history (age, growth, and reproduction), habitat requirements, and
population dynamics (genetic stock structure and natural
During the 1930's and 1940's, statewide blue crab landings were
about 4.5 to 7.0 million pounds with about 1.0 million pounds
reported on the gulf coast. The landings remained relatively
constant through the 1950's and 1960's on the Atlantic coast,
whereas gulf coast landings increased to about 7 millions pounds
during the late 1950's then to 15 million pounds during the 1960's.
Since 1965, the commercial landings of blue crab on both coasts
have declined with the lowest landings reported occurring in 2001
(gulf) and 2002 (Atlantic). Through 2005, landings and commercial
catch rates have rebounded somewhat. Landings were about 7.4
million pounds on the gulf coast and 4.2 million pounds on the
Atlantic coast during 2005.
There are no estimates of the recreational harvest of blue
crabs, making the conclusions of this assessment suspect if these
landings are, as suspected, substantial.
Fishery-independent indices of abundance were variable at the
start of these surveys (1989 or 1990) and showed a depression in
abundance during the early 2000's on both coasts that mirrors the
commercial catch rate trends. These abundance indices have
rebounded through 2005.
All three assessment models indicate that fishing mortality
rates have recently trended downward, since 2003 on the gulf coast
and since about 2000 on the Atlantic coast. The analyses differ
somewhat in the historical level of fishing mortality but all show
a rapid increase in fishing prior to the 1960's then a general slow
increase during the period 1960-1999 before the recent decline.
Estimated abundances of blue crabs appear to have responded to
the recent declines in fishing mortality by increasing since the
early 2000's. Historic trends in abundance show a general decline
in biomass from the 1950's through the 1980's, a possible increase
in abundance and biomass during the early to mid 1990's before a
significant drop is seen during the late 1990's. All three analyses
indicate a rebound in abundance in recent years.
The results of the three analyses point to somewhat different
results for the status of the blue crab stocks in Florida. The
catch-survey analysis indicated that overfishing was not occurring
during 2002-2005, with respect to a rough estimate of the potential
overfishing benchmark F0.1. The biomass dynamic model indicated
that the fishery has been overfishing the stock on both coasts
since the mid 1960's or early 1970's with respect to FMSY. This has
apparently reduced the stock size below the biomass associated with
maximum sustainable yield (MSY). Conversely, the stochastic stock
reduction analysis shows that, though highly uncertain, the stocks
on both coasts were most likely not being overfished during
2002-2005. A common feature in all of these analyses is the finding
that blue crabs in Florida appears to be very resilient to high
fishing rates. Estimates of MSY were consistent between these
models at about 17.5 million pounds on the gulf coast and 7.5
million pounds on the Atlantic coast.
There are troubling gaps in our knowledge about blue crab and
its fishery that could lead to a high degree of bias in these
analyses. The ages of blue crab are not known and may lead to a
biased estimate of natural mortality rate. There is some
information to suggest that commercial discard mortality could be
high and that the recreational catch could be significant. Neither
of these is included in the analyses due to lack of any meaningful
time series of these data.