Otolith Shape as a Tool to Delineate Stock Structure in Gulf of Mexico Greater Amberjack

Greater amberjack Seriola dumerili in the eastern United States are currently managed as two distinct stocks, with one stock residing in the Gulf of Mexico and a second along the Atlantic Coast (including the Florida Keys). Support for independent management of the two stocks is based on both tagging and molecular data. Current management assumes mixing within the Gulf of Mexico stock. However, tagging data suggest that trans-regional mixing may be an infrequent event, and it is possible that some degree of geographic structure exists in the Gulf of Mexico stock. Studies have found otolith shape useful in differentiating between fish stocks of many species. This study examines otoliths of Gulf of Mexico greater amberjack to determine if they differ morphologically among subregions in the Gulf of Mexico. A combination of shape indices and harmonics calculated using elliptical Fourier analysis was used to describe otolith shape. No significant differences were seen between left and right otoliths within the same individual, or between males and females, which implies no significant differences in growth rate between the sexes. Exploration of the data using PCA and cluster analysis indicated no clear regionalization of the stock, supporting single stock management in the Gulf.