Date of Award

8-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Biological Sciences

Advisor

Childress, Michael J

Committee Member

Hains , John

Committee Member

Moran , Amy

Committee Member

Dewalt , Saara

Committee Member

Brown , Bryan

Abstract

Blue crabs make up one of the most important commercial fisheries in the U.S. but there has been some concern over the health of blue crab populations due to large declines in landings seen in recent years. There is a significant positive correlation between river discharge and commercial landings suggesting that drought may be to blame for the recent decline in crab numbers. The work I completed for my dissertation tested multiple hypotheses examining the link between decreasing freshwater discharge, the subsequent rise in salinity, and the abundance of blue crabs in the ACE Basin National Estuarine Research Reserve.
To address these hypotheses, a combination of laboratory studies, field observations, and field manipulations were performed over a four year time period from June 2008 through March 2012. Water quality, crab health, fishing effort, and Hematodinium sp. infection rates were measured quarterly at 27 stations. Field experiments were performed to estimate both blue crab post-larval abundance and survival.
River discharge varied both seasonally and annually causing shifts in the salinity profiles of each river. Increasing salinity increased crab survival, but also increased infection by Hematodinium sp, a lethal dinoflagellate parasite. Post-larval abundance was not related to changes in salinity. Over the four years, crab abundances increased in the river with the highest freshwater input and decreased in the river with the lowest freshwater input. These results suggest that drought can have both positive and negative consequences for crab abundance and that further reductions in freshwater discharge would likely have a net negative impact on future crab landings.

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