Sphyrna alleni, a new hammerhead shark from the Caribbean and the Southwest Atlantic joins the nine previously described species
A new species of hammerhead shark has been discovered in the Western Atlantic, after a specimen thought to be a bonnethead shark (Sphyrna tiburo) was found to have a distinctive head shape, a larger number of vertebrae in its backbone, and significantly different genetic characteristics.
The bonnethead shark, first described by Carl Linnaeus in 1758, is the smallest of the hammerhead species, with males reaching around 85cm and females averaging 95cm.
They have much less pronounced cephalofoils (the ‘hammer’) than other species of hammerhead shark and are sometimes referred to as ‘shovelheads’ in light of their small and rounded heads.
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Bonnetheads are also known for their diets, which includes seagrass, making them one of only a handful of sharks that are known to be omnivorous.
Due to its similarity with the bonnethead, the name ‘shovelbill’ has been proposed for the new species, Sphryna alleni, which has been named in honour of Paul Allen, the late co-founder of Microsoft, whose Global Finprint foundation has continued to provide support for shark conservation following his death in 2018.
The team of scientists, led by Demian Chapman, Director of Mote Marine Laboratory’s Center for Shark Research and co-lead of Global FinPrint, analysed specimens of shark caught by Belizian fishers between 2016 and 2019, intially taking DNA samples for identification, before conducting more thorough physical examinations.
‘DNA analyses provided the first clue that the bonnethead sharks, as we knew them, were at least two species in the Atlantic and not one,’ said Chapman. ‘But DNA alone is not enough to define a species, so we put a team together to look at specimens and see if there were any physical differences as well.’
Lead author of the new study, Cindy Gonzalez, of the Predator Ecology and Conservation Lab at Florida International University, had previously suspected that there were two distinct species of bonnethead when studying sharks in Panama in 2015.
Gonzalez and her team worked closely with the local fishers, collecting specimens for analysis and even turning her apartment into a makeshift lab during the COVID pandemic to carry on her studies during the global lockdown. Eventually, she was able to measure and identify the differences in the number of verterbrae and cephalofoil shape that distinguished Sphyrna alleni as a new species.
‘The fishers and their families became very invested in this process, helping me in collecting tissue samples for genetics and taking hundreds of measurements of these sharks,’ said Gonzalez.
The bonnethead shark is currently listed as Endangered on the IUCN Red List of Threatened Species, making it likely that the shovelbill is similarly under threat. Alll sharks are susceptible to being caught as bycatch, and smaller fish such as the bonnethead and shovelbill are easily taken as indiscriminate bycatch in gillnets.
‘It is imperative to study and protect small hammerhead shark species as they are unique to the American continent and have been extirpated, overfished, and misidentified in fisheries,’ said Gonzalez.
‘At the same time, these sharks have played a critical role in shaping the culture and economy of many local communities in many Latin American countries,’ she added, ‘so it is important to work hand-to-hand with the fishermen on conservation efforts.’
In describing the new species of hammerhead shark, Gonzalez and her team note that bonnetheads have previously been separated into two subspecies, Sphyrna tiburo tiburo in the Western Atlantic Ocean and Sphyrna tiburo vespertina in the Eastern Pacific Ocean, and suggest that the latter may also be a distinct species, and needs further investigation.
The complete study, ‘Sphyrna alleni sp. nov., a new hammerhead shark (Carcharhiniformes, Sphyrnidae) from the Caribbean and the Southwest Atlantic’ by Cindy Gonzalez et al is published under an Open Access license by the online journal Zootaxa.
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