Pacific bluefin tuna population is 'fraction of its 1950s size'
[PALAU] The population of the highly-prized Pacific bluefin tuna has dropped by more than 96 per cent from its estimated level in the 1950s before large scale commercial fishing began and it is unlikely to recover if fishing continues at its current intensity, according to a stock assessment.
The summary of the latest stock assessment report of the fish was released by the International Scientific Community (ISC) for Tuna and Tuna-like Species in the North Pacific Ocean on early this month (8 January).
The study analysed catch data from 1952 to 2011, using these to model the size of the current population and how it has changed over time.
- Overfishing means the number of tuna is estimated be more than 96 per cent lower than in 1952
- The total weight of fish that are at a reproductive age is at or near its lowest level
- But there is no evidence of a sharp fall in adult fish numbers, says expert
Based on the estimates, the Pacific bluefin tuna population is in serious decline because of overfishing and its population is just a fraction of what it used to be. The assessment warns that the population could crash if commercial fishing is not drastically reduced and points out that fishers are now catching mostly juvenile fish.
Gabriel Vianna, a marine researcher at the Australian Institute of Marine Science, says that the practice of excessive fishing and catching juveniles is unsustainable and that there is in an urgent need for better management.
But Sarah Shoffler, a fishery biologist from the National Oceanic and Atmospheric Administration (NOAA), United States, says that there is no solid evidence that there has been a sharp recent fall in the number of Pacific bluefin tuna that survive to maturity.
"While we are very concerned about the population, the NOAA fisheries scientists who worked on the assessment did not determine if the population is near extinction," Shoffler tells SciDev.Net.
But she says it is clear that the total weight of fish that are at a reproductive age is at or near its lowest level.
Pacific bluefin adults reproduce in only two spawning grounds, located off the coast of Japan.
Shoffler says that proper international management should allow the species to recover from its current low level.
US-based campaign organisation the Pew Environment Group says that measures to ensure this happens must include science-based catch limits and major cuts in juvenile bluefin catches by implementing minimum size limits across the Pacific Ocean and banning fishing in the spawning grounds. Robust monitoring and enforcement measures must also be implemented, it says.
At the last meeting of the Western and Central Pacific Fisheries Commission in December, member countries were unable to reach a consensus to limit overall catches of tuna species, particularly the big eye, and failed to ensure the long-term sustainability of the fishery.
Meanwhile, at its June meeting, sister organisation the Inter-American Tropical Tuna Commission adopted the first catch limits for Pacific bluefin tuna in the eastern Pacific. This conservation measure led to the fishery's early shutdown when the limit was exceeded in August.
The full assessment report will be released in late February.
This article has been produced by SciDev.Net's South-East Asia & Pacific desk.