FORT LAUDERDALE/DAVIE, Fla. – They are some of the most iconic and unique-looking creatures in our oceans. While some may think they look a bit “odd,”one thing researchers agree on is that little is known about hammerheadsharks. Many of the 10 hammerhead shark species are severely overfishedworldwide for their fins and in need of urgent protection to prevent theirextinction.
To learn more about a declining hammerhead species that is data poor but inneed of conservation efforts, a team of researchers from Nova SoutheasternUniversity’s (NSU) Save Our Seas Foundation Shark Research Center (SOSF SRC)and Guy Harvey Research Institute (GHRI), Fisher Finder Adventures, theUniversity of Rhode Island and University of Oxford (UK), embarked on a studyto determine the migration patterns of smooth hammerhead sharks ( Sphyrnazygaena ) in the western Atlantic Ocean. This shark, which can grow up to14-feet (400 cm), remains one of the least understood of the large hammerheadspecies because of the difficulty in reliably finding smooth hammerheads toallow scientific study.
To learn about smooth hammerhead behavior, the research team satellite taggedjuvenile hammerhead sharks off the US Mid-Atlantic coast and then tracked thesharks for up to 15 months. The sharks were fitted with fin-mounted satellitetags that reported the sharks’ movements in near real time via a satellitelink to the researchers.
“Getting long-term tracks was instrumental in identifying not only clearseasonal travel patterns, but importantly, also the times and areas where thesharks were resident in between their migrations,” said Ryan Logan, Ph.D.student at NSU’s GHRI and SOSF SRC, and first author of the newly publishedresearch. “This study provides the first high resolution, long term view ofthe movement behaviors and habitats used by smooth hammerhead sharks – keyinformation for targeting specific areas and times for management action tohelp build back this depleted species.”
The researchers found that the sharks acted like snowbirds, migrating betweentwo seasonally resident areas – in coastal waters off New York in the Summerand off North Carolina in the Winter. Their residency times in these twolocations coincided with two environmental factors: warmer surface watertemperatures and areas with high productivity – indicative of food rich areas.
“The high resolution movements data showed these focused wintering andsummering habitats off North Carolina and New York, respectively, to be primeocean “real estate” for these sharks and therefore important areas to protectfor the survival of these near endangered animals,” said Mahmood Shivji,Ph.D., director of NSU’s GHRI and SOSF SRC, who oversaw the study.
Identifying such areas of high residency provides targets for designation as“Essential Fish Habitat” – an official title established by the US Government,which if formally adopted can subsequently be subject to special limitationson fishing or development to protect such declining species.
The tracking data also revealed a second target for conservation. Thehammerheads spent a lot of resident time in the winter in a management zoneknown as the Mid-Atlantic Shark Area (MASA) – a zone already federally closedfor seven-months per year (January 1 to July 31) to commercial bottom longlinefishing to protect another endangered species, the dusky shark. However, thetracking data showed that the smooth hammerheads arrived in the MASA earlierin December, while this zone is still open to fishing.
“Extending the closure of the MASA zone by just one month, starting onDecember 1 each year, could reduce the fishing mortality of juvenile smoothhammerheads even more”, said Shivji. “It’s particularly gratifying to see suchbasic research not only improving our understanding of animal behavior innature but also illuminating pathways for recovery of species and populationsthat have been overexploited so we can try and get back to a balanced oceanecosystem”.
The tracks of the smooth hammerheads (and other shark species) can be foundhere:
The teams’ complete research paper can be found ONLINE.
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