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theses

Hermaphroditic species present unique challenges to fishery managers because the effects of fishing on hermaphroditic population dynamics are not entirely understood. In protogynous hermaphrodites (female to male sex change) the sex ratio varies with size as females change to males. It is expected that male fish have disproportionately high fishing mortality in size regulated fisheries for two reasons. First, males are predicted to be more vulnerable to fishing because they are larger than females and, second, male fish often exhibit aggressive behavior. The implications of prolonged fishing pressure on the population dynamics of protogynous hermaphrodites varies across species. More information about species’ patterns of sex change is needed in order to understand the effects of fishing. This study is divided into two separate chapters: (1) review how sex change is currently handled in stock assessments along the eastern coast of the U.S. in order to identify key data gaps, and to compare hermaphroditic and gonochoristic stock status. (2) Using a tagging study, measure sex selectivity and sex change as a function of size, age, and season in black sea bass (Centropristis striata), an economically important protogynous hermaphrodite in New Jersey and along the East Coast. A review of eleven hermaphroditic stock assessments revealed that sex change is handled in a variety of ways. Despite that no stock assessments assessed sex-specific mortality; hermaphroditic stock status was not any worse off than gonochoristic stock status. In black sea bass, the vulnerability of capturing males and females varied by size and between commercial and recreational fishing gears. For commercial traps, males of intermediate size range (280–360 mm) were most likely to be captured, probability ranged 0.07–0.12. For recreational hook-and-line, male vulnerability increased with size: the largest males (440–500 mm) had the highest change of being captured, probability ranged 0.30–0.60. Across most sizes (129–483 mm), commercial traps captured a significantly higher proportion of males at length compared to hook-and-line fishing gear. Size at 50% sex change was 365 mm and all sex changing females were 3–4 years old. Females that changed sex ranged from 290–370 mm to 342–480 mm. Complete sex change events happened over the winter between the summer spawning seasons in 2011 and 2012, it was expected that slightly less than half (47%) of female black sea bass in 2011 changed sex by the following year in 2012.

ETD_5118

M.S.

Includes bibliographical references

by Mikaela M. Provost

doi:10.7282/T3Q52MN2

ETD graduate

The author owns the copyright to this work.