Non-Lethal Determination of Sex and Maturation in Greater Amberjack

The most recent stock assessment for Gulf of Mexico greater amberjack Seriola dumerili found it to be overfished and undergoing overfishing. Sex-specific spatial distribution and exploitation may be important for greater amberjack because of sex‑specific mortality due to minimum size limits and possible regional skewing of sex ratios. Being able to non-lethally determine the sex of a fish prior to its release in tagging or discard studies would provide needed information on sex ratios, sex-specific migration patterns, and sex-specific mortality rates. To address this issue, a non-lethal method of sex determination was developed using external features of the urogenital pores. Urogenital catheterization was then applied to verify the sex and obtain oocyte samples from females. Of the 194 fish that had their sex verified, 193 were sexed correctly yielding an accuracy of 99.5%. Relative maturation status of females was determined from oocyte samples collected via urogenital catheterization; however no differentiation could be made between immature and resting individuals. This non-lethal method of determining sex and maturation is currently being employed in an ongoing tagging study in an attempt to estimate sex-specific movement patterns and could also be used by trained on-board observers to obtain sex of discarded fish.