Taking a Bite Out of Shark Mortality Rates

Written by on January 2, 2015 in Marine Life, Sharks, Technology

By Hannah Watson

Photo credit: Daniele Colombo via flickr cc.

Bull shark. Photo credit: Daniele Colombo via flickr cc.

Sharks are one of nature’s most vilified predators. Films, television programs, and media reports continue to reinforce the idea that sharks pose a substantial threat to unsuspecting beachgoers. Although it is well known that these risks are often overstated (on average, more Australians are killed per year by kangaroos than by sharks), sharks are rarely portrayed as victims. However, while an average of 6.3 people worldwide are killed by sharks per year, approximately 100 million sharks are killed by humans. Two recent articles published in Global Ecology and Conservation propose shark management solutions to aid in reducing this alarming number.

Beach nets have been used on Australian beaches since the 1930s to protect the public from sharks. These physical barriers reduce the number of shark encounters, but pose significant risks to sharks, which often die after getting caught in the nets. O’Connel et al. examine the effectiveness of an alternative called the Sharksafe Barrier, which uses magnetic barrier technology to exclude sharks from a specific area. Elasmobranches, a subclass that includes sharks, rays, and skates, are sensitive to magnetic fields. O’Connel et al. demonstrate that supernormal magnetic stimuli can have a repellent effect on bull sharks (C. leucas), which are responsible for the majority of near-shore shark attacks. The authors describe the Sharksafe Barrier as an “eco-friendly alternative to beach nets” that can reduce bull shark attacks on humans, and poses less of a risk to the sharks themselves.

In another recent study, Broadhurst et al. consider the threats commercial demersal fishing longlines pose to sharks. While the fisheries examined in this study targeted a relatively common species of Carcharhinid shark for consumption, the authors highlight a number of incidental catches of protected species of shark, including the scalloped hammerhead (Sphyrna lewini), great hammerhead (Sphyrna mokarran) and grey nurse (Carcharias taurus). Broadhurst et al. identify a prospective solution. The authors document how certain species are more likely to be caught at particular times of day; 50% of threatened Sphyrna sharks were caught after sunrise, while 85% of the targeted Carcharhinus sharks were caught before sunrise. As such, the authors propose that short-term, nocturnal deployment of the longlines could significantly reduce the number of incidental catches of protected species. The authors also list bait type, water temperature, and the use of magnetic repellents as factors that might also mitigate by-catch of threatened species.

Despite what films like Jaws would have us think, humans pose a far greater risk to sharks than they do to us. O’Connel et al. and Broadhurst et al. suggest that sharks urgently need protection from threats such as overfishing, bycatch and accidental capture. Both papers propose innovative solutions to these problems, which may go some way toward reducing the staggering number of human-related shark deaths.

To learn more, read the articles:

About the Author: Hannah Watson is an independent science writer currently living and working in Bogor, Indonesia. She has lived in Asia for 6 years and enjoys taking advantage of Indonesia’s beautiful beaches.

Copyright © 2014 by Marine Science Today, a publication of Marine Science Today LLC.

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