Winter mortality in blue crab

In a pair of companion papers, Laure Buaer and Tom Miller quantified the potential impact of witner mortality on the population dynamics of blue crab in Chesapeake Bay. This work was conducted as a part of Laurie's MS thesis.

The first part of the study was a series of lab experiments To calculate survival probability, the mapped winter environmental parameters were combined with a survival model generated from a laboratory experiment (Bauer and Miller submitted). Briefly, juvenile blue crabs, ranging from 14 to 68 mm in size, were exposed to a combination of one of two temperature (3ºC, 5ºC) and salinity (10, 25) treatments for four months (121 days), typical of average wintertime conditions and length of winter in Chesapeake Bay. The survival data were modeled using an accelerated failure model with a Weibull distribution to estimate hazard and survival functions. The survival probability at time t (S(t)) was expressed as the following function of temperature, salinity and size, given by

(3) S(t) = exp{-tλexp[-λ(3.59+0.10(Temperature)+0.02(Salinity)+0.03(Size)]},

where t is the winter duration in days and is a rate parameter.

This statistical model was then used in geostatistical analysis to examine spatial and interannual variability in overwinter mortality. Kriging was used to develop estimates of winter temperature and salinity on a 1x1 km grid throughout the Chesapeake Bay. Maps for each year are available . Predicted survival was highest in the warmer, saline waters of the lower Bay and decreased with increasing latitude up Bay. There was also significant interannual variation with survival being lowest after the severe winters of 1996 and 2003. Similar patterns of survival were observed in a Bay-wide fisheries independent survey; however our experimentally derived survival estimates are consistently lower than survival observed in the field. We combine the survival probability maps with maps of blue crab abundance to show how winter mortality may reduce blue crab abundance prior to the start of the harvesting season

QuaFEL research areas

Recruitment

Blue crab ecology

Multispecies interactions

Fisheries Oceanography

Elasmobranch ecology

Ecotoxicology

Last revised: 4/3/2015