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State of the Field: Is catch-and-release fishing harmful to sharks?

In the wake of the new Marianas Islands shark conservation law, a debate has been raging on the shark  listservs. The law wouldn’t have been possible without support from several local recreational fishermen- people who often take tourists catch-and-release fishing for sharks.

“When I heard of your effort in Hawaii to ban the sale,trade and possession of shark fins I knew if the CNMI was to follow someone with inside connections to the fishing world there had to espouse it and grow it.  They do not like being told what to do from outsiders.  I was not an outsider, and I fished alongside two of the very top level fishermen who happened to be upper level politicians whom I respected.  Rep. Diego Benevente was one of them.  I spoke with him and asked him to introduce a bill which replicated Hawaii’s law, and he did so. I kept constant contact with him and his staff in the effort to see this bill become law.”- Captain William McCue

Image from FishingDestin.info

Many shark conservationists support catch-and-release fishing, claiming that it allows fishermen the thrill of catching a large animal without killing it. Captain McCue reports that in the last 20 years:

“I’ve caught over 300 sharks in the that time a killed four- and if you include spiny dogfish it’s caught well over 2000 sharks and still killed only four- two of which were promptly eaten.”

However, some (such as “My Sunset Rendezvous” author Ila France Porcher) claim that even when a shark is released, the stress from being caught often still causes long-term damage or even death.

“As a shark ethologist, I have personally witnessed sharks who were hooked and fought, and who broke the line, emerge from the ordeal with a jaw so damaged that they lost weight and died over the following weeks or months. A high fraction of sharks caught suffered this fate, and they suffered greatly as a result of this enjoyable passtime pursued by sports fishermen. It would be great news to hear that you switched from a blood sport to a sport that celebrates the life that still remains in our seas, such as diving and photography.” – Ila France Porcher

The arguments are getting increasingly heated, and both sides are relying primarily on personal observations instead of peer-reviewed science:

“I was referring  to my eye witness experiences of sharks I knew over many years….The fact that people are simply not there witnessing and recording what happens to the sharks that you harm should not be considered proof that your practices are not harmful and do not result in the death of the shark later. All animals are delicate organisms, and cannot withstand substantial injury without supportive care. They die. I hope that you will reform your practices and change your ways”- Ila France Porcher

With all due respect to both Captain McCue and Ila, who are both experts in their respective fields, most people are not convinced by personal observations. Peer-reviewed science is something that I find far more convincing. As it turns out, there has been a fair amount of research done of the subject of post-release mortality in sharks.

It is admittedly challenging to study this subject. Most shark research is done from a boat, and once the shark is put back into the ocean, we can’t see it anymore. So how can we determine what happens to it?

There are a few ways to do this. One  is to measure the blood chemistry of the animal while it is still on the research vessel. We know from previous captive studies what a healthy range for metrics like blood pH are, and we know that “exercise” from capture stress alters these metrics. If the shark’s blood pH is within a healthy range when it is released, we can infer that the shark lived. This method isn’t perfect because we don’t know what a healthy range is for all species, and because it doesn’t account for things like infection.

Another method involves tracking the shark with acoustic or satellite telemetry. If it is still moving, it’s still alive. Similarly, a “Crittercam” can be attached to the shark to monitor it’s post-release behavior. These methods are extremely expensive and require larger sharks (they don’t make cameras small enough for some species).

Figure from Skomal et al 2007

Some researchers have begun testing the effects of fishing capture and release on captive animals. Several sharks are placed in captivity and acclimated for days or weeks. Then, researchers “catch” them using standard fishing gear and release them back into their tank. Their post-release behavior can be easily observed in this manner.

The final method is to encounter the sharks you released again at a later date. Though easier said than done, this is  the theory behind mark-recapture studies. Additionally, many species of sharks have a small home range, allowing SCUBA divers to track them down.

Figure 2 from Bansemer and Bennett 2010 showing the time course of a hook-related jaw injury. Photo A is 2006, B is 2007, C is 2008. All are from the same shark

These methods have been applied to a variety of different shark species all over the world. Not surprisingly, whether or not catch-and-release fishing is harmful to a shark depends on a lot of different factors. Some species, like the sandbar shark, are incredibly hardy. I’ve interacted with nearly 400 sandbar sharks for my Masters research, and each one that we released swam away quickly as soon as it hit the water. Blood chemistry research confirms that sandbars are unusually good at recovering quickly from anaerobic exercise. Also, telemetry studies show that Atlantic sharpnose sharks have nearly 90% survivability after release.

Others, like the gummy shark, are relatively fragile. A captive fishing study demonstrated that being caught in a net and released quickly resulted in nearly 70% mortality in this species.

As for Ila’s point about hook injuries? This, too, varies by species. Researchers studying critically endangered Grey Nurse Shark of Australia (what we Americans call sand tiger sharks) found that at one of the few areas where grey nurses are protected, between 29% and 52% of all identified individuals had hook injuries, which varied in severity. However, only 3% of blue sharks off the coast of Long Island had hook injuries (though most injuries were severe).

In summary, although research in this field is ongoing, it seems that both Ila and Captain McCue are both right (and both wrong). Though it varies tremendously by species and location, catch-and-release fishing appears to be more harmful than Captain McCue claimed and less harmful than Ila claimed.

However, as someone else in the listserv discussion pointed out, cooperation with recreational fishermen is essential for shark science and conservation.

“To stop any waste less slaughter, education is the way forward, so anglers that used to kill sharks get involved in tagging and research projects. Competitions can be become a vital source of data, enabling us to learn about migratory routes, stock fluctuations and dynamics etc etc. I help run the Scottish shark tagging programme; we use voluntary shark anglers. We are 50% financed by Scottish Natural Heritage, which is a Scottish Government agency. The analysis of the data will be used to input into shark management plans, implementation of nursery areas, establish commercial closed seasons, MPA’s etc. We put the anglers through a training course as the successful release of the shark is paramount. Our “codes of best practise” have been downloaded and translated into 7 different languages. Organisations like the UK Shark Trust support our work as they realise we can supply the data that no one else can. Peer pressure has changed so much in the UK and anglers are ostracised for killing any shark”- Ian Burret

Ian is absolutely correct. There are a lot more fishing vessels than research vessels, so working with fishermen allows scientists to collect a great deal more data. Tournaments like the Guy Harvey Ultimate Shark Challenge are extremely helpful to scientists.

Additionally, catch-and-release fishing helps make keeping sharks alive valuable. Shark finners claim that they should be allowed to kill sharks because doing so provides jobs. If keeping them alive to catch them for sport and release them also provides jobs, this takes away from the finners’ argument.

In an ideal world, people would appreciate sharks by SCUBA diving with them, and we would stop activities such as catch-and-release fishing which harm some sharks. However, in the real world, I remain a big supporter of catch-and-release shark fishing. It’s a lot better than catch-and-kill-for-no-reason shark fishing.

ResearchBlogging.org

Bansemer, C., & Bennett, M. (2010). Retained fishing gear and associated injuries in the east Australian grey nurse sharks : implications for population recovery Marine and Freshwater Research, 61 (1) DOI: 10.1071/MF08362

BRILL, R., BUSHNELL, P., SCHROFF, S., SEIFERT, R., & GALVIN, M. (2008). Effects of anaerobic exercise accompanying catch-and-release fishing on blood-oxygen affinity of the sandbar shark (Carcharhinus plumbeus, Nardo) Journal of Experimental Marine Biology and Ecology, 354 (1), 132-143 DOI: 10.1016/j.jembe.2007.10.011

Borucinska, J., Kohler, N., Natanson, L., & Skomal, G. (2002). Pathology associated with retained fishing hooks in blue sharks, Prionace glauca (L.), with implications for their conservation Journal of Fish Diseases, 25 (9), 515-521 DOI: 10.1046/j.1365-2761.2002.00396.x

Donaldson, M., Arlinghaus, R., Hanson, K., & Cooke, S. (2008). Enhancing catch-and-release science with biotelemetry Fish and Fisheries, 9 (1), 79-105 DOI: 10.1111/j.1467-2979.2007.00265.x

Frick, L., Reina, R., & Walker, T. (2010). Stress related physiological changes and post-release survival of Port Jackson sharks (Heterodontus portusjacksoni) and gummy sharks (Mustelus antarcticus) following gill-net and longline capture in captivity Journal of Experimental Marine Biology and Ecology, 385 (1-2), 29-37 DOI: 10.1016/j.jembe.2010.01.013

Gurshin, C., & Szedlmayer, S. (2004). Short-term survival and movements of Atlantic sharpnose sharks captured by hook-and-line in the north-east Gulf of Mexico Journal of Fish Biology, 65 (4), 973-986 DOI: 10.1111/j.0022-1112.2004.00501.x

Hight, B., Holts, D., Graham, J., Kennedy, B., Taylor, V., Sepulveda, C., Bernal, D., Ramon, D., Rasmussen, R., & Lai, N. (2007). Plasma catecholamine levels as indicators of the post-release survivorship of juvenile pelagic sharks caught on experimental drift longlines in the Southern California Bight Marine and Freshwater Research, 58 (1) DOI: 10.1071/MF05260

Morgan, A., & Carlson, J. (2010). Capture time, size and hooking mortality of bottom longline-caught sharks Fisheries Research, 101 (1-2), 32-37 DOI: 10.1016/j.fishres.2009.09.004

Skomal, G., Lobel, P., & Marshall, G. (2007). The Use of Animal-Borne Imaging to Assess Post-Release Behavior as it Relates to Capture Stress in Grey Reef Sharks, Carcharhinus amblyrhynchos Marine Technology Society Journal, 41 (4), 44-48 DOI: 10.4031/002533207787441999