0711 Quantification of unobserved injury and mortality of Bering Sea crabs due to encounters with trawls on the seafloor

We will apply and improve existing methods for collecting crabs immediately after trawl encounters (Rose 1999). Assessments of reflex impairment will be used to more efficiently estimate delayed mortality rates with reduced requirements for long-term holding (Davis 2006). This project leverages pilot funding from the NMFS cooperative research program.

Pilot fieldwork in early Summer 2007 will establish recapture net designs and handling, as well as procedures for holding crabs onboard. Reflex and reflex impairment observations of captive animals at the Kodiak NMFS laboratory will provide information needed for field assessments of crab condition. The principal fieldwork in Summer 2008 will combine these developments to assess the mortality probabilities of crabs that have passed the sweeps, wings and central footrope of a commercial groundfish trawl as well as control animals collected identically without trawl encounters. Mortality estimates will be derived by combining condition assessments based on reflex impairments with the delayed mortality rates of retained animals.