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Taking Stock of Pacific Sharks

FAO/The Common Oceans ABNJ Tuna Project

By IW:LEARN

February 24^th, 2019

It is both the best and worst of times for the world’s open ocean sharks. On the upside, more people than ever before are recognizing the importance of conserving these majestic and valuable top marine predators. Many national and international organizations now have specific measures in place designed to manage shark catches and trade. Regulations and campaigns around the globe have discouraged the consumption of shark fin soup, and this may help to stamp out the wasteful practice of shark finning.

But on the downside, there are still many critical issues to tackle. Worldwide tuna and billfish catches continue to increase year-on-year, and sharks are caught right alongside them by the same fishing gear. Unlike these target species, sharks lack the ability to recover quickly from overfishing due to their much slower growth and lower reproductive potential. Fisheries data that are not species-specific or that do not record all sharks caught continue to make it difficult to decide when urgent management actions are needed.

Recognizing the problems and aiming to contribute to the solutions, the GEF-funded Common Oceans ABNJ Tuna Project of the Food and Agriculture Organization (FAO) kicked off a five-year work plan for shark data improvement and assessment in 2014 and will wrap up its activities in the next few months. Assessment activities focused on the Pacific Ocean - as that is where two-thirds of the world’s tuna catches are taken - and resulted in four new shark assessments each with a unique and ground-breaking outcome.

The first shark in the line-up was the southern hemisphere porbeagle. Although there is great concern about the status of the northern hemisphere porbeagle, the status of its southern hemisphere cousin, which is smaller and lives twice as long, has been poorly understood because of the dispersed, circumpolar extent of its range. Assessing the southern stock for the first time involved working across oceanic and organizational boundaries with collaborators from Argentina, Chile, Japan, New Zealand and Uruguay. Unlike in the north, the study found there is a very low risk that the southern stock is subject to overfishing. This may be because many of the adults are found in waters south of 45 degrees south, and as there is very little fishing in the area it can serve as a refuge.

The project next moved north to the tropics to assess the iconic bigeye thresher shark. This species is very susceptible to fishing pressure – it only gives birth to two pups in each reproductive cycle – but due to the low quantity and quality of data stock assessment was considered impossible. Undeterred, the Common Oceans ABNJ Tuna Project entered into data confidentiality agreements with fourteen countries to compile a comprehensive dataset and to calculate the risk of overfishing in a fine-scale grid across the Pacific. In doing so the Project identified a new “hotspot” of abundance southwest of Hawaii. Overall, the study suggests there is a 20-40% chance that overfishing is occurring when applying a highly conservative threshold, and as high as 80% chance when using less conservative one.

For the third assessment the two international management bodies for tuna fisheries in the Pacific agreed to collaborate to update the status of silky shark. Their work led to a peer-reviewed paper showing that large fluctuations in the abundance of juvenile silky sharks are correlated with oceanographic conditions and don’t necessarily reflect true population abundance. The team then devised an innovative way to incorporate oceanography into the assessment model and found that at least part of the stock is not currently overfished as previously thought.

The fourth and final assessment was for the whale shark, an ocean giant that often gets caught up in purse seine operations, and according to regulations adopted several years ago must be safely released from the net. The Project team applied a novel approach to predict habitat suitability and whale shark densities across the Pacific by analyzing this species’ interactions with the purse seine fishery as recorded by fisheries observers. The study findings align well with known ‘hotspots’ for whale sharks and suggest that the risk from Pacific Ocean fisheries alone is moderate to low.

Like the global situation for sharks, the Common Oceans ABNJ Tuna Project results report a mixture of good news and bad news for Pacific shark stocks. The southern hemisphere porbeagle, silky and whale sharks do not appear to require major new management interventions, but the risk to bigeye thresher is high and as yet unabated. Beyond these specific results, the Project has demonstrated the viability of new, cross-jurisdictional partnerships and data-sharing arrangements. It has also generated a number of methodological advances that can be applied to other regions and a broader array of data-deficient species impacted by fishing. Dr Shelley Clarke, Technical Coordinator-Sharks and Bycatch for the Project notes:

“We’ve made some great technical gains over the last five years, and now the remaining challenge is to better integrate sharks into the mainstream of the fisheries management dialogue so that we can ensure they are sustainably utilized and conserved”.

Dr Shelley Clarke giving a presentation on her work at the Nausicaa High Seas International Conference, in June 2018. Credit: Nausicaa

2019 will be the final year of implementation of the Common Oceans ABNJ Program that is part of the GEF International Waters Portfolio. Learn more about how this unique partnership has contributed to sustain international waters cooperation by harnessing the efforts of a large and diverse array of partners, including governments, inter-governmental organizations, non-governmental organizations and private sector, and achieve responsible, efficient and sustainable fisheries production and biodiversity conservation in the areas beyond national jurisdiction (ABNJ) here.