Selective Fishing Pressure on Large Male Blue Crabs Negatively Affect Small Size, Sex Ratio, and Population Reproductive Potential in the Upper Chesapeake Bay.

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Title: Selective Fishing Pressure on Large Male Blue Crabs Negatively Affect Small Size, Sex Ratio, and Population Reproductive Potential in the Upper Chesapeake Bay.
Author: Carver, Adina Motz
Advisors: Thomas G. Wolcott, Co-Chair
Donna L. Wolcott, Co-Chair
Anson H. Hines, Committee
Abstract: A male-focused size-selective fishing pressure has the potential to reduce the average size of the males in the population, reduce the density of males in the population, and/or raise the sex ratio of females to males. All of these may affect the mating dynamics of the population by reducing the amount of sperm that males provide to females and decreasing the number of males available for copulation. I used three different approaches to investigate the effect of the fishery on the population. First I collected paired and unpaired crabs from the field to investigate crab size and seminal stores in nature. This approach substantiated that male blue crabs subjected to heavier fishing pressure are smaller, and that smaller males pass less sperm and accessory fluid to females. It also demonstrated that although the most depleted males in the population are not mating, some that continue to form pre-copulatory pairs are as sperm depleted as males that had just completed copulation.My second approach involved the use of biotelemetry to monitor mating behaviors in the field. Tracked males demonstrated a proportionately greater amount of pairing behavior than tracked prepubertal females, which is consistent with expectations of crab behavior in a population with a female-biased Operational Sex Ratio. My third approach was to examine a long-term trawl data set for trends over time. A decline in the average size of mature males (carapace width >110 mm) and an increase in the operational sex ratio of pre-pubertal females to mature males (carapace width >110 mm) and pre-pubertal females to legally fished males (carapace width >127 mm) were found at one of the four trawl locations. The observed trends in size and sex ratio at that trawl location are as would be expected in a population where an increasingly intense fishery has been removing large males. Analysis of seminal stores in conjunction with the crab behaviors and population trends provides evidence that the fishery is in fact having a detrimental affect on the reproductive potential of the blue crab population.
Date: 2001-11-20
Degree: MS
Discipline: Marine, Earth and Atmospheric Sciences
URI: http://www.lib.ncsu.edu/resolver/1840.16/2263


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