Latitudinal Trends in Sex Ratio and Sperm Counts of Blue Crabs in the Chesapeake Bay

Latitudinal trends in sex ratio and sperm counts of blue crabs in the Chesapeake Bay.

Sarah Rains (rains@cbl.umces.edu, 410-326-7355)

Michael Wilberg (wilberg@cbl.umces.edu, 410-326-7273)

Thomas Miller (miller@cbl.umces.edu, 410-326-7276)

Jennifer Humphrey (humphrey@cbl.umces.edu, 410-326-7355)

University of Maryland Center for Environmental Sciences, Chesapeake Biological Laboratory

The blue crab Callinectes sapidus is the most important commercially harvested species in the Chesapeake Bay.  Due to their importance and concern about potential recruitment overfishing, regulations to conserve females were adopted in 2008.  The potential effects of the new regulations on the functional sex ratio for mating have raised concerns over the possibility of sperm limitation.  Our objective was to characterize differences in sperm counts and sex ratios among tributaries of the bay.  We collected female blue crabs from six tributary rivers of Chesapeake Bay: the Chester, Choptank, Patuxent, Potomac, York, and James.  Each tributary was sampled 2-6 times, with catches of between 50 and 200 female blue crabs, on a biweekly schedule during September - November of 2011.  For each collection, the ratio of adult males to adult females was recorded and females were frozen for preservation.  We removed and preserved the spermathecae and ovaries before counting both eggs and sperm storage numbers within them.  We then compared the sex ratio and sperm counts of females among river systems.  Preliminary results indicated a north-south trend in sex ratio, with a higher proportion of males in northern tributaries, and that average sperm counts varied among tributaries.