Integrated responses of crustaceans inhabiting estuaries to the challenges of feeding and digestion in low salinity

This study presents a methodology for combining archival data storage tags (DSTs) and ultrasonic transmitters to investigate the microhabitat conditions of adult Cancer magister (Dana), inhabiting an estuary. The temperature, salinity and depth experienced by freeranging Dungeness crabs was recorded at 10min intervals for periods ranging from 1 week to 8months. Crabs were tracked using a hydrophone and tags were recovered via concentrated trapping or returned by recreational fishers for a reward. These methods led to a return rate of 50%. Representative CTD tag data showed that the conditions recorded at fixed stations within the estuary were not reflective of those experienced by free ranging crabs, but rather crabs were able to orient and avoid low salinity within the estuary. The prevalence of low salinity exposure was linked to times of increased food availability within the estuary, suggesting that crabs were entering the shallows of the estuary to forage. The techniques employed in this study demonstrate that DSTs are a viable means of determining the microhabitat conditions of crustaceans inhabiting highly variable environments. This work has been published as: Curtis, D. L. and McGaw, I. J. (2008). A year in the life of a Dungeness crab: methodology for determining microhabitat conditions experienced by large decapod crustaceans in estuaries. Journal of Zoology 274, 375-385.