“No tuna disaster” as global stocks deemed healthier than expected

Fishing effort in most tuna fisheries has grown steadily in recent years, a trend that has been largely led by the constantly increasing purse-seine harvest. At the same time, these stocks remain in a healthy state and are much less overfished than many other coastal resources, delegates heard at the sixth European Tuna Conference in Brussels, Belgium.

Speaking at the biennial forum, held on the eve of the 2017 Seafood Expo Global, Alain Fonteneau, a renowned tuna fisheries scientist from the French Research Institute for Development (IRD), confirmed that the total global tuna catch has grown to a level of around five million metric tons (MT), with skipjack accounting for around 66 percent the total. 

Fonteneau highlighted that the purse-seine fleets’ heightened productivity – averaging 2.5 percent annually over the last two decades – was chiefly responsible for this growth and that their improved efficiency was directly due to the increased number of fish aggregating devices (FADs) deployed in recent years. 

Over the last 10 years, FADs have been responsible for approximately 50 percent of the total purse-seine catch, including 53 percent of the skipjack that has been caught during this period.

“If we were to lose all of the FAD fisheries tomorrow, we would lose most of the skipjack catch,” he said.

While the amount of skipjack caught in most fisheries has continued to increase – a trend that Fonteneau said is indicative of healthy stocks – most of which are still not yet exploited to their maximum sustainable yield (MSY), including the 2 million MT currently coming from the Western Pacific. He is, nevertheless, pessimistic about the Indian Ocean’s stock, despite it currently being in “good shape,” as his “personal feeling” is that the next stock assessment, expected in October, will suggest its over-exploitation.  

But, he acknowledged, providing stock assessments of the short-living skipjack are “an extremely difficult, almost impossible task.”

With regard to the status of the other main tuna species, Fonteneau said that most bigeye stocks are estimated to be close or slightly over the levels of full exploitation, yellowfin is mostly considered to be close to MSY, most albacore are in “relatively good shape,” and despite a total catch below 100,000 MT, bluefin tuna is today being “quite well managed” and not at risk today.

Again, there are “frequent serious uncertainties” in many stock status analyses, he said, explaining that even the best scientists using the best stock assessment software struggle to estimate real stock status. This is due to a number of factors, not least because tuna migratory patterns are complex and highly variable and therefore cannot be properly handled by statistical models.

All of the stock statuses obtained by RFMOs are only ever best estimates of the stock status obtained at a given moment and in given scientific and political contexts. Furthermore, many of the results – comparing past and present stock assessments – have been proven to be wrong over time but are still used in a lot of current analyses, he said. 

“In my view, many of the projections are therefore totally unrealistic,” Fonteneau said. “If we don’t understand the past, how can we make a projection for the future?”

Fortunately though, all tuna stocks have proved to be “very robust” and “very difficult to heavily overfish,” even when the tuna RFMOs struggle to reduce the overcapacity of fisheries, Fonteneau said.

Consequently, none of the 21 major tuna stocks have shown signs of a critical collapse.

This biological resilience is due to tuna’s very large habitat, encompassing millions of square nautical miles, as well as their large-scale migrations, their flexible feeding behavior and “frequent cryptic biomass” that cannot be fished. In addition, all tuna demonstrate efficient reproduction, he said.

“There is no tuna disaster. Most stocks are fished close to MSY, but there is no single example of total collapse and no risk of such in the short-term. Most tuna resources are under the control of the RFMOs, although they have lost control of the FAD capacity,” Fonteneau concluded. “More than ever, there is a need to keep control of the stocks’ status so they are not put at risk.”