Revised population figures still spell doom for tuna

(PhysOrg.com) -- An international team of marine scientists, including three at Simon Fraser University, hope their latest findings about the perilous state of the world’s tuna populations do not dampen efforts to conserve them. 

Maria José Juan-Jordá, Nick Dulvy, Andrew Cooper and Iago Mosquiera say the world’s tuna populations are down 60 and not 90 per cent as previously thought, compared to their abundance in the 1950s.

A 2003 study, published in Nature, concluded that large pelagic fishes, mainly tuna, had been reduced by 90 per cent.

The revised population figure in the latest study, Global population trajectories of tunas and their relatives, has been published in the journal Proceedings of the National Academy of Sciences.

Juan-Jordá is the study’s lead author and a member of SFU’s Earth to Ocean Research Group. Dulvy is an SFU biology professor, co-supervisor on Juan-Jordá’s doctoral thesis at a Spanish university and co-chair of the Shark Specialist Group at the International Union for Conservation of Nature. Cooper is an associate professor of fisheries science and management at SFU’s School of Resource and Environmental Management. Mosqueira is a fisheries scientist at the European Commission’s joint research centre. 

The four researchers say, regardless of whether the world’s tuna populations are down 60 or 90 per cent, most of them have been fished down close to the limits of sustainability.

“By pooling together the most accurate abundance estimates of tuna populations we found that our analyses differ from the more pessimistic interpretations of the global status of tuna fisheries described in the past”, says Juan-Jordá.”

The latest study’s authors emphasize that allowing further expansion of catches in these fisheries will jeopardize their future existence. 

“The long term sustainability of tuna fisheries could be improved if managers were to step back and treat the sustainability levels as limits to be avoided rather than a bull’s eye to be hit,” says Cooper.

Dulvy notes valuable species of tuna are the most overfished and therefore fisheries management needs the backing of international conservation treaties to effectively conserve them. 

“The standard argument against listing fishes under CITES (Convention on the Trade in Endangered Species) is that fisheries management will take care of them,” says Dulvy.

“Well, here we have a case where trade is overwhelming the normally effective scale of fisheries management. There is clearly a role for international conservation treaties to work alongside fisheries managers to halt further declines in the overfished bluefin tunas.”