Thanks to decades of intentional, science-based management, the United States boasts some of the best managed and most sustainable shark fisheries in the world. To accomplish this, scientists must constantly update the life history parameters (i.e., the age and growth estimates, and the size and age at maturity estimates) for shark species in all the areas they occur. Moreover, specimens of all sizes (from newborns to mature adults) are needed from both sexes. As you might imagine, this is no small task! Recent collaborations provide a blueprint for how this can be accomplished using blacktip shark (Carcharhinus limbatus) as an example.
Working collaboratively with fisheries researchers at Texas A&M Galveston (TAMUG), members of the Mississippi State University (MSU) Marine Fisheries Ecology Program and the Mississippi-Alabama Sea Grant Consortium (MASGC) recently concluded a reproductive biology study, as well as an age and growth study, on blacktip sharks across the Gulf. Blacktip sharks are wide-ranging, so this required collecting blacktip shark samples from Texas, Louisiana, Mississippi, Alabama and Florida. Samples collected by TAMUG and MSU/MASGC scientists were supplemented with samples from commercial fishermen using a variety of fishing gear.
Differences occur between eastern and western Gulf
In total, samples were collected from more than 1,000 sharks. Results from both studies highlighted differences between blacktip sharks caught in the western Gulf (e.g., off Texas) versus those caught in the eastern Gulf (e.g., off Florida). These results confirmed that in general, blacktip sharks are moderately long lived, reaching nearly 20 years of age. As is the case for many shark species, females reach slightly larger sizes and grow a bit slower than males. In addition, males and females in the western Gulf reached maturity at smaller sizes and younger ages than blacktip sharks in the eastern Gulf.
Why is this important?
Slower growing, longer-lived species can withstand less fishing pressure than faster growing, shorter-lived species. In other words, the life history characteristics of a species indicate how resilient the population is to overfishing. An important finding from these two studies was that the life history characteristics of blacktip sharks in the western Gulf differ from those in the eastern Gulf, adding to a growing body of evidence suggesting these might be different stocks. Accordingly, NOAA Fisheries currently sets higher quotas for blacktip sharks in the western Gulf compared to the eastern Gulf. Science-based management decisions like this help to ensure the sustainability of Gulf blacktip sharks.
Meet the author
Amanda Jargowsky
Marine Fisheries Specialist
Amanda Jargowsky is a marine fisheries specialist with the MASGC-supported Marine Fisheries Ecology Program at the Mississippi State University Coastal Research and Extension Center. She conducted... Read more
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