Shark depredation: An Easy Meal That’s Hard to Digest

by Harisson Carmody

Our fisheries provide us with both the fresh seafood we love as well as an important recreational activity which, in Australia, for example, over 3 million people participate in every year (Baker 2017).  However, we are currently being reminded that we also share this resource with other creatures who need it just as much if not more than us.

So, what is shark depredation and how does it relate to this? Shark depredation occurs when a fishing catch is partially or completely consumed by a shark before it can be retrieved by the fisher. Though other marine predators such as toothed whales, bony fish, seals and even seabirds have been recorded depredating catch, sharks and toothed whales are thought to primarily be the main groups responsible (though more evidence is required to verify this). Though depredation can lead to a relatively easy meal for sharks, its broader impacts are generally negative. These impacts include damage to fishing gear, injury and sometimes death to the shark and additional mortality of the consumed fish (which more often than not is unrecorded in fishery data).  Because of these impacts, depredation has become a pressing issue in many fisheries worldwide.

Depredation is one of many kinds of interactions that humans have with predators such as sharks on a daily basis. We are now very much a part of their world, yet our relationship with their world is difficult. For example, shark depredation is noted as a major point of concern by recreational and commercial fishers in Western Australia, and in Australia more broadly, with some stating that it has reached the point that recreational and commercial fishing in some areas is now unfeasible. Recent research indicates that shark depredation is higher in areas of greater commercial and/or recreational fishing effort; potentially because sharks, which are known to be very intelligent, have subsequently learnt to follow fishing (and other) vessels in the hope of a meal (Mitchell et al. 2018, Carmody et al. 2021). As such, in areas where the concentration of fishing effort is high, the potential for depredation likely increases.

Many have suggested either re-opening a previously closed shark fishery in the affected areas or introducing a shark cull as a solution to the problem. Understandably, fishers are concerned about their livelihoods, and this is seen as a direct and straightforward answer to the issue. However, depredation, and human-wildlife interactions more broadly, are complex problems. In this sense, removing sharks are likely to cause more problems of their own rather than providing an overall solution, considering the vital role they play in the management of marine ecosystems by regulating food chains. As such, consultation between both fisheries scientists and fishers themselves is required to come up with other suitable solutions.

The key to this problem and other human-wildlife interactions is the relationship humans have with wildlife; particularly wildlife that we have little to no understanding of. For shark depredation, if all stakeholders understood the vital role that sharks play in maintaining marine ecosystems, and had rigorous scientific research providing information on the population status of the shark species of concern, then there might be greater support for other solutions. In this case, these solutions include physical protection devices or deterrents on fishing lines and changes to fisher behaviour, such as moving site regularly, using electric reels to retrieve fish to the boat quicker, not dumping fish waste, avoiding areas or depths where certain shark species are more likely to occur, and avoiding fishing close to other boats. Currently, however, this knowledge is not readily available and scientific research in this area still has many questions to answer. So how do we go about finding solutions to these problems? Education. Education of stakeholders, so that they understand exactly what role sharks (or any other forms of wildlife) play in the marine ecosystem more broadly; and how their complete removal would likely cause several more problems much greater than the one they are currently dealing with. Education of scientists, so that firstly we can try and answer some of the many questions we still do not have the answer too, and secondly so that we can understand the viewpoint of particular stakeholders to better work with them to find more appropriate solutions that, hopefully, will keep everyone happy (and provide a much easier meal to swallow, including for the sharks)!

To learn about some of our work relating to impacts on the fishing communities in Thailand, depredation and discarded fishing gear, check our collaborative citizen science project ‘MARsCI’ here!

  • Baker, E. 2017. Recreational fishers in Australia: A social snapshot 2017. Prepared by Elizabeth Baker on behalf of the Fisheries Research & Development Corporation and Ozfish Unlimited.
  • Mitchell, J.D., McLean, D.L., Collin, S.P., Taylor, S., Jackson, G., Fisher, R. and Langlois, T.J. 2018. Quantifying shark depredation in a recreational fishery in the Ningaloo Marine Park and Exmouth Gulf, Western Australia. Marine Ecology Progress Series 587: 141–157.
  • Carmody, H., Langlois, T., Mitchell, J., Navarro, M. and others. 2021. Shark depredation in acommercial trolling fishery in sub-tropical Australia. Marine Ecology ProgressSeries 676: 19-35.