The practice of catch-and-release may be dangerous for sharks, according to a study published in the scientific paper Conservation Physiology. Researchers from Trinity College Dublin, in Ireland, determined that the temperature of these predators spikes after being released, which may affect their health and behaviour in the wild.
Sharks found around the Irish coast are often caught by recreational anglers and then released back into the water. However, researchers don’t know the long-term effects that this practice can have on these animals, many of which are critically threatened.
A team of researchers from Trinity College Dublin, Ireland, worked closely with anglers to determine how the catch-and-release practice may affect shark behaviour and physiology in sharks found in the Bahamas, off the coast of Cape Cod in the USA, and in Irish waters around Co. Cork.
The researchers caught sharks using rod-and-reel and baited hooks and then inserted thermometers into a muscle to see if their body temperature changed (animals were not harmed during this procedure). They also attached biologging devices to the fins to record body and water temperature after the animals were released back into the wild.
“The temperature measurements we took show that catching sharks on a line resulted in rapid spikes in their body temperature, with one blue shark showing an increase of 2.7°C in just a few minutes – which, in physiological terms, is a huge elevation,” said Lucy Harding, first author of the study. What’s more, it took up to minutes to cool down after the animals were released.
As the sharks in this study — Blue shark and Tiger shark — are considered cold-blooded, their body temperature should match the water temperature where they’re swimming. It’s very unusual to see such increases under normal circumstances.
“Results like these illustrate the physical exertion sharks undergo during catch-and-release fishing. We don’t yet know whether the rapid, fishing-induced heating has a damaging effect on shark physiology, but it’s something that is important to study in more detail in the future, “ concluded Nick Payne, Assistant Professor in Trinity’s School of Natural Sciences. “Results from these studies could be used to design best handling practices for shark angling going forward; if we can adopt the least stressful fishing methods, then it’s a win for the sharks and also for future generations of anglers.”
Lucy Harding, Austin Gallagher, Andrew Jackson, Jenny Bortoluzzi, Haley R Dolton, Brendan Shea, Luke Harman, David Edwards, Nicholas Payne, Capture heats up sharks, Conservation Physiology, Volume 10, Issue 1, 2022, coac065, https://doi.org/10.1093/conphys/coac065