Tens of millions of ocean-dwelling sharks are caught by fishing each year, causing catch population declines for many species. Yet oceanic shark fishing still remains largely unregulated. One factor hampering current conservation efforts of sharks is a scarcity of information on where sharks are likely to encounter fishing vessels.
Now, however, a new study involving PML scientists has found that sharks tend to gather in locations with strong temperature gradients and abundant food sources. These ‘hotspots’ of activity (also known as ocean fronts) have been located through tracking the sharks’ satellite data tags and from remote sensing images of the ocean environment provided by PML.
Interestingly, the scientists also found that fishing vessels and sharks targeted similar locations, thus increasing potential shark susceptibility to fishing exploitation in these areas. In this study, an international team of researchers from the UK, Portugal, Spain and U.S.A. tracked more than 100 sharks from six different species by satellite across the entire North Atlantic, one of the most heavily exploited oceans. Concurrently the scientists tracked 186 Spanish and Portuguese longline fishing vessels using GPS to quantify the overlap in space and time with the sharks.
PML’s Dr Peter Miller who contributed to the study commented: “Unfortunately the sharks’ use of fronts to find good foraging areas in the vast ocean also puts them at higher risk of being caught. I hope that my techniques for analysing fronts on satellite images can assist conservation efforts.”
The researchers propose that because current hotspots of shark activity are at particularly high risk of overfishing, the introduction of catch quotas or size limits will be necessary to protect oceanic sharks that are commercially important to fleets worldwide at the present time.