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Implications of a decrease in the mature size of female blue crab, Callinectes sapidus

by 1976- Davis, John Howell

Abstract (Summary)
DAVIS, JOHN HOWELL. Implications of a Decrease in the Mature Size of Female Blue Crab, Callinectes sapidus. (Under the direction of Donna L. Wolcott.) The size-at-maturity of female blue crabs is declining and the proportion of very small mature females ( < 100mm carapace width (CW)) is increasing in North Carolina. Decreasing mature size of the female may have an effect on the mating success and mortality of size-disparate mating pairs. To test the effect of body size on mating behavior, I used controlled mating experiments comparing size-disparate mating pairs with similarly-sized mating pairs. Small males handled large females longer than any other mating pair combination; however, no increase in injury or mortality was found. Neither large nor small males transferred significantly different numbers of sperm to large and small females. Sizedisparity appears to have no effect on mating success in blue crabs, suggesting that diversity of size-related genotypic traits can be preserved in the population. I also designed a mathematical model to estimate the lifetime spawning potential of different size-cohorts of female blue crabs subject to different mortality pressures. Cohorts of very small females ( < 100mm CW) that are not subject to fishery mortality produce 5.1 – 58.1% more eggs over two spawning seasons than larger, harvestable females (127-159mm CW), suggesting an evolutionary advantage to maturing at smaller sizes. I also used the model to estimate the efficacy of a proposed restriction on the commercial harvest of large females ( > 172mm CW), intended to increase the spawning potential of large females in order to increase populationwide recruitment, as well as the number of recruits that may possess a larger-size genotype. The proposed seasonal (Sept. – Apr.) commercial harvest of large females produced an estimated 23.2 – 35.1% increase in egg production over two spawning seasons. However, since the large females compose less than 2% of the population, on average, the estimated increase in spawning potential for the entire population was negligible (0.46%). Additionally, the 5% tolerance of the regulation allows for the harvest of the entire population of large females, suggesting that the proposed restriction will be ineffective. Implications of a Decrease in the Mature Size of Female Blue Crab, Callinectes sapidus by John Howell Davis A thesis submitted to the Graduate Faculty of North Carolina State University In partial fulfillment of the Requirements for the degree of Master of Science Marine, Earth and Atmospheric Sciences Raleigh, NC 2006 Approved by: Thomas G. Wolcott David B. Eggleston Donna L. Wolcott Chair of Advisory Committee
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School:North Carolina State University

School Location:USA - North Carolina

Source Type:Master's Thesis

Keywords:north carolina state university

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