While the Gulf is home to an assemblage of coastal sharks, the great hammerhead is perhaps the most iconic. Growing a maximum of 16 feet long, this species is long-lived and is distinguishable by its large, sickle-shaped dorsal fin and broad, straight, hammer-shaped head (called a cephalofoil).
Despite its renowned status, little is known about great hammerhead life history (traits related to reproduction and survival) and movement patterns in the Gulf, even though this is a well-established part of its range. Many elasmobranchs (including great hammerheads) exhibit slow growth, late age-at-maturity, and low fecundity (the number of offspring produced), making them highly vulnerable to fishing pressure, habitat degradation and climatic changes.
Despite a lack of a directed fishery in the United States, great hammerheads are caught as incidental bycatch, and are highly suspectable to the physiological effects of capture stress. This leads to high rates of fishing mortality – even if they are carefully and quickly released after capture.
That is why marine fisheries specialists jumped at the opportunity to sample a deceased great hammerhead on Friday, April 21, in Orange Beach, Alabama. Members of the City of Orange Beach Coastal Resources team reached out to Dr. Marcus Drymon, a marine fisheries specialist with the Mississippi-Alabama Sea Grant Consortium and an assistant extension professor at Mississippi State University, to coordinate gathering valuable data from such a unique specimen.
Marine fisheries specialists examined the shark’s exterior condition, documenting external injuries, parasites or abnormalities. The shark’s heart, liver, esophagus, stomach and scroll valve were also closely inspected for signs of trauma or disease. Valuable reproductive information was taken from both uteri (yes, sharks have two uteri!), the ovary and the oviducal glands – an organ integral to fertilization and reproduction. The scientists were surprised to find that this large female, measuring over 14 feet in length, was also gravid (pregnant), carrying 40 great hammerhead pups!
After initial examination, a myriad of samples was taken to further investigate aspects of the large female shark and her pups. For example, several vertebrae were removed to determine the shark’s age and birth location and to elucidate information on great hammerhead population structure and connectivity. Muscle tissue samples will allow scientists to determine feeding habits and evaluate heavy metal and microplastic contamination.
Finally, fin clip samples taken from both the mother and all forty of her pups will be used to distinguish relatedness between the pups. Additionally, these fin clip samples will contribute to a current study examining genetic population structure of great hammerheads and the number of breeding individuals within the Gulf population.
While unfortunate, stranding instances like these represent rare opportunities for scientists to investigate the biology and ecology of a particular fish and its population, and in some cases, evaluate ocean conditions and the health of coastal ecosystems. The extensive amount of information collected from this individual and her pups will enhance our knowledge of great hammerheads in the northern Gulf and contribute to effective conservation efforts for this incredible species.
Meet the author
Ana Wheeler
Extension Associate, Mississippi State University
Ana Wheeler conducts bottom longline surveys off Alabama and Mississippi waters, manages the data collection and analysis from the surveys and contributes to peer-reviewed journals and... Read more
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