Impacts of density-dependent predation, cannibalism and fishing in a stage-structured population model of the blue crab in Chesapeake Bay

TL;DR

This study uses a stage-structured model to analyze how density-dependent predation, cannibalism, and fishing influence the resilience and population dynamics of blue crabs in Chesapeake Bay, challenging assumptions of population collapse.

Contribution

It introduces a comprehensive model incorporating density-dependent factors, showing blue crab populations are resilient and unlikely to exhibit bistability or extinction under realistic conditions.

Findings

Bistable states are unlikely with realistic parameters.

Hyperbolic fishing does not cause extinction within observed densities.

Density-dependent predation and cannibalism increase population resilience.

Abstract

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.