MOSSEL BAY NEWS - An important study that Oceans Research Institute in Mossel Bay contributed to, indicates that the worrying news for sharks worldwide is there is no refuge for them where industrialised fishing does not take place.
Large sharks inhabiting the open ocean, only account for over half of all identified shark catches globally in target fisheries or as by-catch.
Regional declines in abundance of some populations, have led to a call for limits on catches in the high seas, or areas beyond national jurisdiction, where there is currently little or no management. Precise knowledge of where, in the expanse of the oceans, sharks aggregate and how commercial fishing affects this, was vague, despite it being crucial knowledge in conservation.
Global study
The study, published in Nature, a leading science magazine, was led by Professor David Sims, based at the Marine Biological Association Laboratory in Plymouth, United Kingdom, as part of the Global Shark Movement Project.
An international team of more than 150 scientists from 26 countries took part in the study, collating movement data from nearly 200 sharks tracked with satellite transmitters.
Unprecedented detail allowed the scientists to map out positions and reveal hot spots while also plotting the location of pelagic shark longline vessels worldwide. These consist of fleets of large, longline vessels with the type of fishing gear that catches most pelagic sharks. Each vessel can deploy 100km long lines, bearing 1 200 baited hooks daily.
The study found multi-species pelagic shark hotspots were mostly located in frontal zones, between different water masses that are highly productive and food-rich.
It was found that 24% of the mean monthly space used by sharks globally falls under the footprint of pelagic longline fisheries.
This means, on average, any shark runs the risk of being caught every seven days.
The overlap for commercially exploited sharks is even bigger, with an average of 76% of their space used. The white shark and porbeagle shark, internationally protected species, had overlap values exceeding 50%.
Professor Sims stated that the results show major high sea fishing activities currently centred on ecologically important shark hotspots worldwide.
Local reaction
"This is a vitally important study. Scientists can finally provide results that force governments to look at changing policies in terms of marine conservation," says Dr Enrico Gennari of Oceans Research Institute, who with his team, contributed to the study, through data collected since 2012.
It not only, according to Dr Gennari, means inroads for impacting policy in South African waters, but opens the door to negotiate with other African countries along the East Coast, where for instance, no protection of white sharks is currently in place.
"In terms of the results of the study, it basically means that not a week goes by, without a shark being under threat of being caught." Gennari says Oceans Researsh is thrilled about having made a contribution towards a study that could impact worldwide policy.
He also says that the study results highlight the necessity of tagging sharks in order to track their movement and migration, in particular species under threat.
"There has always been a debate on tagging. This proves in fact that we cannot do without the information provided through tagging."
He explains that the data used in the global study was originated through satellite tagging, but he suggests the information from acoustic tagging could be as useful in future studies. This approach gives a more regional view of shark movement and coastal migration as opposed to a global overview. This, he says will prove particularly useful in determining why white shark populations in Gansbaai, Struisbaai and False Bay have noticeably declined.
Dr Gennari says that even though the white shark population in Mossel Bay, according to his research, remains stable, it does not mean we won't see the same happening to Mossel Bay.
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