Spatial variability in the fecundity of Atlantic sharpnose sharks (Rhizoprionodon terraenovae) in the northern Gulf of Mexico

Spatial variability in life history characteristics, including age at maturity, growth rates, and reproductive periodicity, has been documented for a number of shark species. Among causative factors hypothesized to induce dissimilarities, clinal variation is most often linked to temperature. However, if spatial differences in prey abundance were the causative factor, it could be masked by clinal variation. If prey abundance is the actual driver, intraspecific differences should be evident over a broad longitudinal range (i.e., constant water temperature) characterized by a demarcation of low and high productivity. In this study, Atlantic sharpnose sharks (Rhizoprionodon terraenovae) were collected for 1 year throughout the northern Gulf of Mexico (GOM) by using standardized bottom longline gear. Reproductive data were collected from 253 gravid females, and mean (4.2 versus 3.4 embryos) and median (4 versus 3 embryos) brood sizes were higher west of longitude 88°W than to the east. Based on fisheries survey data, spatial trends in abundance of Atlantic croaker (Micropogonias undulatus), a common prey item, coincided with that of Atlantic sharpnose sharks, and both were more abundant west of 88°W. Although differences in brood sizes appear minor, potential lifetime reproductive output for females was calculated to be over 2 times greater in the western versus the eastern GOM.