|Austin Gallapher works up a bullshark|
A new study led by scientists at the University of Miami (UM) Abess Center for Ecosystem Science and Policy and the Rosenstiel School of Marine and Atmospheric Science investigated how several species of coastal sharks respond to stress from catch-and-release fishing. The results revealed that each of the shark species responded differently. Hammerhead sharks were by far the most vulnerable to fighting on a fishing line.
The UM scientists experimentally simulated catch-and-release fishing on five shark species – hammerhead, blacktip, bull, lemon and tiger sharks – in South Florida and Bahamian waters. Researchers took blood samples to examine stress, including pH, carbon dioxide and lactate levels, conducted reflex tests, as well as used satellite tags to look at their post-release survival. Fighting on a fishing line significantly affected the blood lactate levels of sharks, similar to what happens to humans during intense or exhaustive physical exercise, which has been linked to mortality in many species of fish. The study revealed that even with minimal degrees of fighting on a fishing line, hammerhead exhibited the highest levels of lactic acid build of all species studied, followed by blacktip, bull, lemon and tiger sharks. Tagging results also suggested that, after release, hammerheads were also prone to delayed mortality.
"Our results show that while some species, like tiger sharks, can sustain and even recover from minimal catch and release fishing, other sharks, such as hammerheads are more sensitive" said lead author and Abess Center Ph.D candidate Austin Gallagher. "Our study also revealed that just because a shark swims away after it is released, doesn't mean that it will survive the encounter. This has serious conservation implications because those fragile species might need to be managed separately, especially if we are striving for sustainability in catch and release fishing and even in bycatch scenarios."
Adds study co-author Dr. Neil Hammerschlag, a Research Assistant Professor at UM, "Many shark populations globally are declining due to overfishing. Shark anglers are some of the biggest advocates for shark conservation. Most have been making the switch from catch and kill to all catch and release. Our study helps concerned fisherman make informed decisions on which sharks make good candidates for catch and release fishing, and which do not, such as hammerheads."AOV: This study has some policy implications, especially for hammerheads. How are hammerheads currently managed in South Florida and the Bahamas?
Angelo O'Connor Villagomez had the chance to catch up with Austin Gallagher to ask some follow up questions about his new study and what the results could mean for fishermen.
|Austin Gallagher, Angelo O'Connor Villagomez, David Shiffman, and Eden Villagomez.|
AG: There are definitely some strong take-home messages that could help augment existing policy or even forge new initiatives. We found that hammerhead sharks respond poorly to fishery-related stressors, which is important data for managing them not only in Florida but in the greater Atlantic. In the Bahamas great hammerheads are protected from commercial harvest, and in Florida state waters they are a prohibited species. This means that if you are within state waters and catch a hammerhead (great, scalloped, or smooth, the first two of which have similar stress responses to fishing), it must be released. However our data show that these species are prone to higher mortality, which may undermine this policy measure even if they are released. Thus, I hope this data will be looked at carefully if we are striving for sustainable practices that are presumably designed to allow overfished populations of sharks the time to recover.
AOV: Can you explain how your study proved that hammerheads were prone to delayed mortality? And what does that mean?
AG: We know that animals can suffer delayed mortality hours to days after they are released from fishing gear. But to answer this question for our sharks - including hammerheads - we had to affix satellite tags to the sharks. We showed that their reporting rates (the sharks pinging in to orbiting satellites) were significantly lower than both bulls and tigers. Tiger sharks never suffered delayed mortality - and the rates of reporting dropped in the first 2 weeks but did not change up to 4 weeks. We assume this is related to delayed post-release mortality. It is my hope that these data points contribute to the conservation of these highly sensitive-to-fishing species. As a side note, when we discovered this phenomenon happening, we actually altered our research fishing methods to give any hammerheads the best chance of survival after release - including the use of vitamins and steroid injections when they are caught.
AOV: So would recommend that fishermen not target hammerheads? Is there a way for fishermen to reduce the interactions they have with hammerheads, or to target the more hardy shark species?
AG: The reality is that most anglers want to catch hammerheads. They are large, fascinating, and scary to most people. I think people will always try to target them. I think the best take home message here is that if you want that resource to exist in the future, anglers have a responsibility to act in accordance with the scientific information that now exists. If you catch a hammerhead, you need to be prepared on how you are going to release it quickly. The best practices would be to bring it in fast, keep it in the water, remove the hook swiftly or cut the line and let the animal swim away. If you use the right gear (hooks, lines), then there can be minimal impacts on the animals here and the gear will likely fall out shortly thereafter. Cutting the line quickly if the animal is fighting hard is also probably a good idea. If the State of Florida is serious about protecting hammerhead sharks from mortality in their state waters, then perhaps a species-specific policy is needed - this could range from a moratorium on catch and release for this species, to mandatory regulations on how the animal is caught.
AOV: Thanks, Austin. Anything else you'd like to share?
AG: You can find out more info, videos, and read the scientific publication at www.sharktagging.com.