The hidden consequences of catch-and-release sport fishing

In an effort to protect sensitive fish species, many recreational fisheries have adopted catch-and-release practices, where fish are returned to the water after being caught. 

However, excessive fishing pressure may influence the behavior of target species and jeopardize the sustainability of fisheries. 

An international team of biologists, co-led by the University of Massachusetts Amherst and the University of South Florida, along with conservationists and industry partners in Seychelles, set out to determine if this is the case. 

The study revealed that a prized sport fish, the giant trevally, is susceptible to high fishing pressure. 

This conclusion emerges from a “natural experiment” during the COVID-19-induced closure of the fishery, carrying significant implications for managing the species across the Indian and Pacific oceans.

Collaboration for sustainable fishing practices

Study senior author Andy Danylchuk is a professor of fish conservation at UMass Amherst. 

“A few years ago, both the Island Conservation Society, which promotes conservation in the Seychelles Islands, and the Alphonse Fishing Company (now known as Blue Safari Seychelles Fly Fishing), a flyfishing guide service located in the Seychelles, approached my group concerned about the sustainability of sportfishing in the Seychelles,” explained Danylchuk.

“It was the perfect convergence of a research question that my team cares deeply about – how recreational fishing can be a sustainable part of the ‘blue economy’- brought to us by stakeholders looking to implement policies and management guided by science.”

Unintended consequences of sport fishing 

Unlike harvest-oriented recreational fishing, which directly affects population numbers, catch-and-release sport fishing is intended to minimize mortality – theoretically leaving more fish in the water for future anglers. 

However, this method can have unforeseen effects. These include increased mortality from hooking fish in critical areas like the gills, post-release predation, altered movements, and “hook shyness.” 

Hook shyness occurs when fish become accustomed to being targeted and subsequently avoid lures or flies, potentially reducing catch rates. This behavioral change is particularly concerning for the giant trevally, a highly sought-after species that attracts anglers willing to spend significant amounts for a memorable catch. 

Declining catch rates due to hook shyness could disappoint anglers and negatively impact the local tourism industry. In some cases, local guides might resort to baiting fish with chum to lure them closer, exacerbating behavioral and movement alterations in giant trevally.

Investigating sustainability through natural experiments

Study lead author Lucas Griffin completed this research as part of a post-doctoral fellowship at UMass Amherst. Griffin is now an assistant professor of marine biology at the University of South Florida. 

“The Island Conservation Society and the Alphonse Fishing Company wanted to know whether or not the current fishing practices for giant trevally in the Alphonse Group of islands in the Seychelles was sustainable,” said Griffin. 

“And so, we’ve been working with them on a series of studies to assess just that.”

The research team utilized acoustic telemetry – implanting transmitters in giant trevally and placing receivers throughout the coastal environment to track individual movements – and a mark-and-recapture program, which involved collaborating with anglers to implant microchips in fish. 

These methods allowed the team to monitor how often and where individual fish were caught and released.

Once-in-a-lifetime natural experiment

Originally, the researchers planned to conduct short-term closures of various fishing spots to observe giant trevally behavior under natural conditions. 

However, the COVID-19 pandemic led to an almost two-year shutdown of recreational fishing in the Seychelles, providing an unprecedented natural experiment. 

“It’s strange to say, but the pandemic created a once-in-a-lifetime natural experiment,” Griffin remarked. “The entire fishery shut down, so we could really see how giant trevally live in the total absence of fishing pressure.”

How fish respond to increased pressure

The study found that while giant trevally can adjust their behaviors and movement patterns in response to fishing pressure, they did not significantly alter their behavior during the short-term closures or the extended COVID-19 shutdown. 

Over time, however, there is evidence that increased fishing pressure may lead to hook shyness, with some groups of giant trevally shifting their home ranges away from prime fishing spots. 

Conversely, the mark-and-recapture data indicated a substantial population of giant trevally, with new individuals entering the fishery potentially offsetting the effects of hook shyness.

Balancing fishery health and angler satisfaction

Overall, the evidence suggests that while giant trevally exhibit resilience to the immediate impacts of catch-and-release, sustained fishing pressure can influence their behavior in ways that may reduce catch rates and affect the angling experience. 

Maintaining a healthy ecosystem and ensuring high populations of giant trevally could enhance their resilience to angling pressures.

“We are part of the ecology of these fish,” Griffin said. “If we want to be catching more of them, we may need to consider limiting the number of anglers that target them in any given location.”

Implications for fisheries management

The findings highlight the necessity of integrating scientific research with fisheries management practices to ensure the long-term sustainability of sport fishing. 

By understanding the behavioral responses of target species like the giant trevally, stakeholders can develop informed strategies that balance conservation efforts with economic benefits from tourism and sport fishing. 

This study underscores the importance of adaptive management approaches that consider both ecological dynamics and human interests in recreational fishing.

Enhancing the sustainability of sport fisheries

Moving forward, the research team plans to continue monitoring giant trevally populations and behaviors, particularly in relation to varying levels of fishing pressure. 

Further studies will aim to refine management practices to mitigate the unintended consequences of catch-and-release fishing and enhance the sustainability of sport fisheries. 

By encouraging collaboration between scientists, conservationists, and industry partners, the team aims to promote practices that support both the health of fish populations and the livelihoods of communities dependent on recreational fishing.

This comprehensive approach ensures that sport fishing remains a viable and sustainable activity, preserving the giant trevally and other sensitive species for future generations of anglers and maintaining the ecological integrity of coastal regions.

The study is published in the Canadian Journal of Fisheries and Aquatic Sciences, 

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