Remedies for overfishing saved tuna and billfish, but sharks remain at risk for extinction

(CN) — Overfishing has been threatening the ocean ecosystem for almost as long as commercial fishing has existed, but despite modern attempts to hold back the loss of species and genetic biodiversity in our oceans, some species remain at risk. To measure and track the extent of damage, researchers have developed a continuous indicator for annual variations in marine health.

Maria José Juan-Jordá and colleagues present a Red List Index in the journal Science on Thursday that focuses on tuna, billfish and sharks. The index looks back all the way to the 1950s, assessing changes in extinction risk throughout the decades. The index is intended to be a robust and responsive guide for established fishery commissions and organizations internationally.

Juan-Jordá, lead author of the paper and coordinator of the project, explained in an interview, "They need indicators to monitor progress. The Red List Index is already a well established indicator, it’s already adopted by global processes, but it was not estimated for marine species. We are providing this global indicator so countries can use it to track progress and sustainability goals."

The index was developed as a collaboration between the Basque Country based AZTI Technology Center, Simon Fraser University and the International Seafood Sustainability Foundation.

The study pins tunas, billfishes, and sharks as markers for overall ocean health. The study explained that these particular predatory fish are identified as necessary to maintain the delicate balance of the natural marine ecosystem and are a relatively data rich group of species, due to commercial interests. Beyond the possible extinction of several species, a reduction of these populations would compromise ocean resilience, which could have resounding effects on human food security and the economies of countries that rely on fishing.

The index indicates an increasing extinction risk for the predatory fishes throughout the past 70 years, until the last decade or so, when more responsible methods were implemented, and conservation efforts ramped up to stymie overfishing internationally, leading to a recovery in tuna and billfish populations.

However, sharks, which are particularly sensitive and vulnerable to fishing effects, have not been able to enjoy the same rate of recovery as their fellow fish; rather, extinction risk for sharks has only continued to worsen, even as they have begun to receive more statistical attention.

"Sharks have not been a priority for these organizations," Juan-Jordá said. "It's difficult because the data is not there. Historically, countries have been relatively good collecting fishery statistical data for tuna and billfishes because they are the target fishes, they are the priority. Sharks have historically never been a priority. So the data collected for sharks is very poor."

Analysis of 52 populations of 18 different species of tuna, billfish and sharks through the Pacific, Atlantic and Indian Oceans determined that shark bycatch is a major contributor to the shark’s lagging behind in population recovery.

The study establishes that sharks are often collateral damage for fisheries, who regulations and methods target species like tuna do not cover incidental catches, like sharks or sea turtles. While methods for more responsible catching have been the subject of significant policy reform and conservation efforts, non-target species still end up dead and discarded by the fisheries.

Reducing incidental bycatch of sharks is complicated by political concerns. The study still pushes for more international regulation and management of incidental catch, despite complexities in the international policy making. The study points to the tuna and billfish as indication that this kind of restoration can be replicated with the sharks.

"Overfishing remains the main threat to shark populations, because the species are incidentally caught in tuna fisheries and other fisheries. They’re completely undermanaged globally," Juan-Jordá said. "What we’re advising is that we need to redefine priorities. You already have goals and targets to ensure sustainable fisheries for target species but this needs to be hand in hand with goals for biodiversity. They need to redefine priorities, they need a more effective management measures to reduce shark mortality effectively, including mitigation measures, including science-based catch limits, including operations among countries for better data collection and evaluation."

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