Temporal and spatial variation in sperm stores in mature female blue crabs Callinectes sapidus and potential effects on brood production in Chesapeake Bay

Abstract

Fisheries that selectively harvest males have the potential to diminish the reproductive success of females due to reductions in the transfer of sperm and seminal fluid during mating. The purposes of this study were to investigate variation in sperm and seminal fluid quantities obtained during mating in mature female blue crabs Callinectes sapidus in Chesapeake Bay, USA, and to model potential effects of sperm reduction on lifetime brood production. We explored variation in sperm and seminal fluid quantity with respect to (1) season, (2) location, (3) operational sex ratio (OSR), (4) relative time since mating, and (5) fertilization, and used this information to model brood production. Mature female blue crabs were obtained from targeted or long-term collection efforts. Crabs were characterized by carapace condition, presence of a sperm plug (hardened seminal fluid), and presence of egg masses or egg remnants. They were dissected and processed to determine the quantity of stored sperm and spermathecae weight. Sperm quantity, but not spermathecae weight, of recently mated females varied seasonally and spatially, and was positively correlated with OSR. Females received as many as 3 x 10(9) sperm during mating, which declined to an average of 8 x 10(7) sperm before fertilization of the first brood. Both model simulations and estimates of sperm used for fertilization derived from sperm counts of females with and without evidence of spawning indicated that a reduction in lifetime brood production (sperm limitation) is likely in individual female blue crabs if they survive to a second spawning season.