Fishing
Yellow Fin Tuna Stock Under Threat
It's shrinking by as much as 50 percent
The Pacific's yellowfin tuna stock could be sliding down to the point of joining the lengthening world list of fish stocks destroyed by overfishing. Yellowfin is an important part of the region's US$2000 million a year tuna industry.
The Western Pacific's stock of yellowfin tuna has shrunk by as much as 50 percent since the mid 1990s for reasons not yet understood, according to the Pacific Community's Oceanic Fisheries Programme (OFP). More intensive fishing could cause the dwindling of numbers of the big tuna, as could shifts in ocean environment caused by such weather impacts such as the El Nino/La Nina conditions.
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Fisheries scientists say that until more research shows the cause of the yellowfin tuna stocks decline, there should be a freeze on the present level of fishing it, particularly the catching of juvenile fish. Yellowfin, which can grow to well in excess of 100 kilogrammes, amount to about 23 percent of the Western Pacific total catch of nearly 1.9 million metric tonnes of four species of tuna - skipjack, yellowfin, albacore and bigeye.
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Scientists for several years have been expressing alarm about overfishing of bigeye, which is the smallest part of the total catch, but has an annual market value of probably more than US$1000 million. The 2000 bigeye catch in the Western Pacific was reported at 114,907 metric tonnes and has been climbing since 1998. According to the Oceanic Fisheries Programme, research on the impact of fishing on bigeye needs priority and that fishing for it should also be frozen. First hints of concern about the condition of the yellowfin stock began to be made several years ago. Alarm about the trend for yellowfin is expressed in a record of last year¹s meeting of the Standing Committee on Tuna and Billfish, which is the main forum for the annual discussion of tuna fisheries science, and for which the Noumea headquartered Pacific Community's Oceanic Fisheries Programme is the secretariat.
This says that the annual yellowfin catch first exceeded 200,000 metric tonnes in 1980. By 1990 it had almost doubled to 380,000 metric tonnes. In the past four years it exceeded 420,000 metric tonnes with a peak of 480,000 metric tonnes.
Scientist say that while changes in yellowfin catch rates may be affected by the shifting patterns of the El Nino effect, which causes ocean temperature to change, the bigger catch could also be the product of improved fishing techniques. Tagging of yellowfin in the early 1990s, when catches were 10 to 20 percent below present levels, indicated that the stock was not being overfished.
But recent research shows that the stock has suffered a "significant" decline of about 35 percent since 1997. The decline is "most evident" in the western equatorial Pacific where the stock is estimated to be down by more than 50 percent since the mid 1990s. For the whole Western Pacific, the stock is estimated to be 30 percent below what it would have, had it not been fished. There's still not enough scientific knowledge to be certain about what is happening to yellowfin tuna numbers. But it is possible that present catches may not be able to be maintained, the scientists say.
Skipjack tuna, the least valuable species, amount to about 65 percent of the total annual catch or about one million metric tonnes. The 2000 catch was 1.2 million metric tonnes and, say the scientists, there's no worry about the security of the species.
"Their fast growth, early maturity, high fecundity, spawning year around, relatively short life span, highly variable recruitment and few age classes on which the fishery is dependent, makes the species unique among the main tuna species."
