  The blue crab (Callinectes sapidus) is a dominant ecological species of high
commercial value. Spawning stock and recruitment of the Chesapeake Bay
population declined by 80% in the 1990s. After severe management actions were
implemented in 2008, female abundance rebounded to pre-1994 levels and
stabilized. The stepwise decline in the early 1990s, followed by a consistently
low level of abundance for 15 y and a jump to high abundance after 2008,
suggested the existence of alternative stable states. Alternatively, high
fishing pressure combined with low recruitment in 1992 could have triggered a
proportional decline in the population, followed by a population increase in
2008 due to rigorous management actions that reduced fishing. We evaluated
these alternatives with a stage-structured dynamic population model using
ordinary differential equations. In addition, stock assessment models assume
that fishing and mortality are independent of density. Hence, we also
investigated the role of density-dependent predation, cannibalism and fishing
in blue crab population dynamics. We conclude that for the blue crab population
in Chesapeake Bay: (1) bistable positive states are not likely with
biologically realistic parameter values; (2) hyperbolic (depensatory) fishing
will not produce extinction at the range of population densities observed in
the bay; and (3) crabs can survive a higher fishing rate under the more
realistic assumption of sigmoidal (density-dependent) predation and cannibalism
than under constant (density-independent) predation and cannibalism. These
collectively indicate that the blue crab population in Chesapeake Bay is
resilient to a range of biotic and abiotic disturbances.
