Assessing ecological connectivity of blacktip sharks (Carcharhinus limbatus) in the Gulf of Mexico using stable isotope analysis of multiple tissues

Effective management of blacktip sharks relies on a comprehensive understanding of population distribution and stock structure. Previous stock separations and the implementation of regional quotas have proven successful in maintaining the sustainable harvest of blacktip sharks in both the Western North Atlantic and United States Gulf of Mexico (US GoM), in commercial and recreational fisheries. Within the US GoM, finer scale biological separation between blacktips in western and eastern regions has been supported through tagging, genetic, and diet data. This study provides additional evidence of unique ecological isotopic niche areas and δ15N and δ13C values for blacktip sharks from the western, central, and eastern US GoM across muscle and vertebral tissues that reflect different isotope turnover rates. Blacktip sharks from western and central regions exhibited isotope values and niches that were significantly smaller compared to eastern sharks, with enriched δ13C and depleted δ15N west of 88ºN. Ontogenetic shifts were noted for most regions and there was no crossover or overlap in average isotope values from early to recent life between regions. These spatiotemporal patterns suggest that in the year following birth and prior to the time of capture, blacktip sharks on the central and western shelves have separated ecologically from blacktips on the eastern US GoM Florida shelf.