Scientists Highlight Concerns About Sharks Caught and Released by Recreational Fishermen

New marine scientist study raises possible red flags for sharks caught and released by recreational fishermen.

The researchers revealed that when the ocean's famous predators are caught, their temperatures rise, which may have physiological and behavioral consequences.

Fishing for sharks

(Photo : Jakob Owens/Unsplash)

Sharks are often captured and returned to the ocean by recreational fishermen and scientists throughout the Irish coast and around the world, as per ScienceDaily.

However, as catch-and-release fishing becomes more common, do we know enough about the effects this technique may have on the health and well-being of the creatures, many of whom are critically endangered?

Lucy Harding, a Ph.D. student at Trinity College Dublin's School of Natural Sciences, and her international team of collaborators worked directly with shark angling operators to assess how catch-and-release fishing might affect shark behavior and physiology in sharks swimming in the Bahamas, off the coast of Cape Cod in the United States, and in Irish waters around Co. Cork.

The researchers used rod-and-reel and drum lines (baited hooks) to catch sharks and then implanted thermometers into muscles to test if their body temperature was changing.

They also affixed biologging devices to shark fins, which captured data, such as body temperature and water temperature, before releasing the sharks back into the wild.

Lucy, the first author of the related study paper, which was just published in the journal Conservation Physiology, stated:

"The temperature measurements we collected reveal that hooking sharks on a line resulted in dramatic jumps in their body temperature, with one blue shark exhibiting an increase of 2.7°C in only a few minutes - which is a substantial elevation in physiological terms."

Because the sharks in this research (the Blue shark, Prionace glauca, and the Tiger shark, Galeocerdo cuvier) are "cold-blooded," their body temperatures tend to mirror the temperature of the water in which they travel.

As a result, such an elevation is exceptional.

The study also discovered that it might take up to 40 minutes for the sharks to calm down after being put back into the ocean.

According to Nick Payne, Assistant Professor at Trinity's School of Natural Sciences: "These findings highlight the physical strain that sharks face when caught and released. We don't know whether quick, fishing-induced heating harms shark physiology, but it's something that has to be studied more in the future."

These massive, rapid spikes in body temperature look aberrant in the context of what these animals normally encounter, and the scientists hope their findings may aid in treatment.

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The magnitude of recreational fishing

Recreational fishing differs from commercial fishing in that the major motivation for involvement is leisure, however, this does not stop the catch from being caught for household consumption, as is frequently the case, as per Oxford Academic.

This definition excludes the numerous people in poor countries who fish as part of artisanal or subsistence fisheries for the sole purpose of gathering food.

Although fishing participation rates and the amount of catch retained for eating vary by location (up to 90% in Scandinavia), the return from recreational fisheries is substantial.

If recreational fishing participation statistics in Canada from 2000 mirror global trends, this activity is enjoyed by around 11.5% of the world's population.

Assuming a worldwide human population of 6.33 billion, comparable extrapolations of Canadian recreational capture rates would imply that 47.10 billion fish are landed globally each year, with 36.3% (17.09 billion fish) caught, weighing 10.86 million metric tons (assuming a mass of 0.635 kilograms per fish).

When both commercial inland and marine finfish fisheries are included, worldwide harvest rates total 80.47 million metric tons per year.

When the harvest from these two sectors is added together, worldwide fish harvest rates may be around 14% greater than current commercial data indicate.

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