Science Serving Maryland's Coasts
Michael Wilberg, Ph.D.
Chesapeake Biological Laboratory
Examination of the Effect of Sex, Age, and Maturity on Winter Blue Crab Distributions in the Chesapeake Bay
The blue crab Callinectes sapidus is an economically and ecologically important species in Chesapeake Bay. While past studies have examined blue crab spatial distributions of density and habitat partitioning in small-scale environments, none have examined con-specific factors affecting large-scale winter blue crab distributions throughout Chesapeake Bay. My study was conducted to describe large-scale blue crab spatial distributions in Chesapeake Bay that may be useful in future management efforts of blue crabs in Chesapeake Bay and Chesapeake Bay as a whole. Using data obtained from the annual winter dredge surveys in Chesapeake Bay, I created maps to examine spatial distributions of blue crab catch per unit effort (CPUE) and differences in habitat use between male, female, mature female, immature female, age-0, age-1+, age-1+ male, and age-1+ female blue crabs. Regression analyses were performed to determine the effect of the presence of one category of blue crabs on the presence of another. Winter spatial distribution and habitat partitioning of blue crabs in Chesapeake Bay were consistent with studies of blue crab habitat use conducted by Ramach et al. (2009) in the Rachel Carson National Estuarine Research Reserve and Hines et al. (1987) in the Rhode River subestuary. Male and juvenile female blue crabs have similar winter spatial distributions in Chesapeake Bay with a strong positive correlation between their CPUE values, indicating these classes of blue crab have a high degree of spatial overlap. Several hypotheses could explain this pattern including attraction between the sexes or similar habitat or environmental preferences. Age-0 and age-1+ blue crabs overlap substantially in their winter habitat use in Chesapeake Bay and their CPUEs were positively correlated. Immature female and mature female blue crabs were negatively correlated and occupied different areas of Chesapeake Bay; this difference was likely due to the migration of mature females to the mouth of Chesapeake Bay for spawning. The presence of different categories of blue crabs do not explain the winter spatial distributions observed. Further studies may be necessary to determine environmental factors driving winter blue crab distributions in Chesapeake Bay.
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