A new analysis shows that the habitats of three shark species (large hammerhead sharks, tigers and bull sharks) are relatively well protected against longlines in federal waters for the southeastern United States, but that some prime locations are still vulnerable to fishing.
The new study led by researchers from the Rosenstiel School of Marine and Atmospheric Science at the University of Miami (UM) has important implications for the further protection of this type of risk against unintentional fishing, known as bycatch, in federal waters of the United States.
Great hammerhead sharks are considered overfished and experienced population decline in the subtropical Atlantic and the Gulf of Mexico. Tigers and bull sharks have experienced declines in the region to a lesser extent in recent decades and their populations now seem to be stabilizing.
The research team analyzed data from 96 tagged large hammerhead sharks, tiger and bull sharks to create models for habitat suitability that reveal specific areas where these sharks are most likely to occur due to favorable environmental conditions. These "highly suitable habitats" were then compared to areas where longlines with gears are currently forbidden to determine which part of their habitats is protected from and vulnerable to longline fishing activity.
The analysis showed that highly suitable habitats that overlap with longline fishing are dependent on species and season. Very suitable habitats of large hammerhead sharks and tiger sharks were relatively well protected against pelagic longlines and yet vulnerable to bottom fishing. Both species were also vulnerable to fishing for pelagic fisheries and long-line fish from southwestern Florida. Accordingly, the researchers suggested that prolongation of longline limits for this area could benefit both large hammerhead shark and tiger shark species.
"This study emphasizes the importance of considering seasonal trends in habitat use and movement patterns, as these can vary greatly throughout the year and affect the effectiveness of management plans for these species," said the lead author of the study, Hannah Calich , a UM Rosenstiel School alumna and current Ph.D. student at the University of Western Australia.
"Given the divergent movements of many migrating sea creatures, the extent to which management areas protect their most important habitats is often unknown and certainly very challenging to determine," says Neil Hammerschlag, a researcher at the Rosenstielschool at UM and is studying co-author. "We hope that our approach will be useful for researchers working with other migratory species, such as sailfish, turtles, whales, seals and tuna, to better assist in addressing these conservation issues."
The study, entitled "Overlap between habitat suitability and longline management areas shows vulnerable and protected habitats for highly migratory sharks", was published on August 23 in the magazine Marine Ecology Progress Series.
The authors of the research are: Hannah Calich, Maria Estevanez and Neil Hammerschlag from the UM Rosenstiel School of Marine and Atmospheric Science.
The study was supported by The Batchelor Foundation, Disney Conservation Fund, Wells Fargo, Guy Harvey Ocean Foundation and the West Coast Inland Navigation District.
Material delivered by University of Miami Rosenstiel School of Marine & Atmospheric Science. Originally written by Diana Udel. Note: content can be edited for style and length.