Scientists: Pacific Bigeye Tuna Population in Steep Decline

Scientists have released new assessments of tuna populations in the western and central Pacific Ocean, and the results include several troubling developments for the world’s largest tuna fishing grounds.

According to figures released by the Western and Central Pacific Fisheries Commission (WCPFC) Scientific Committee in late July, the total tuna catch in 2013 was estimated at over 2.6 million metric tons. Furthermore, the numbers of some tuna species left to reproduce are dwindling, dropping to dangerously low levels in some cases.

The region’s most recent assessment of bigeye tuna confirms that less than 20 percent of the population remains. 

That’s a significant development, because fishing nations have agreed that a population size this low “represents an unacceptable risk” to the stock, scientist John Hampton, who leads the program that conducted the assessments, was quoted as telling the Pacific News Center. And while the longline catch of bigeye dropped to its lowest rate since 1996, the purse seine catch increased to its highest rate.

“The continued decline of the bigeye population is a clear sign that the region’s current conservation management measures are just not working,” said Amanda Nickson, director of global tuna conservation for The Pew Charitable Trusts.

Purse seine vessels use fish aggregating devices (FADs) to attract and ultimately catch skipjack tuna with their large nets, but the use of floating objects also lures juvenile bigeye tuna. Countries that are members of the WCPFC have agreed to a seasonal closure of the FAD fishery to reduce the catch of juvenile bigeye, but scientists have warned for several years that this measure would not bring the population back to healthy levels.

“The latest science eliminates any doubt as to the urgent need for fishing nations to reduce levels of FAD fishing,” Nickson said. “It is vital that commission member countries agree to a rebuilding plan for bigeye tuna, one that is based in science with a high probability of success.”

In April, scientists reported that the Pacific bluefin tuna population was just 4 percent of its unfished size, and the unsustainably high catch of juveniles—the smallest fish—threatens the species’ continued existence.

Populations of yellowfin and skipjack tuna in the western and central Pacific are at acceptable levels, according to scientists, but there is concern that catches should not be allowed to increase. It's particularly troubling that large vessels continue to enter the fishery. 

According to a document presented during the meeting of the Scientific Committee in August, the number of purse seine vessels chasing tropical tuna in 2013 reached an all-time high (297 vessels), and overall fishing effort was also at its highest.

The report of the WCPFC Scientific Committee meeting will be used to inform management decisions when commission members meet in December in Apia, Samoa.