Pacific Bluefin Tuna Stock Assessment

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Scientists recently completed a new, improved stock assessment of the Pacific bluefin tuna population which suggests that the stock was still quite low in 2014, although up from 2012 numbers.

The Pacific Bluefin Tuna Working Group of the International Scientific Committee for Tuna and Tuna-Like Species in the North Pacific Ocean (ISC) including scientists from government fisheries agencies of the region (Japan, Korea, Mexico, Taiwan, USA) and the Inter-American Tropical Tuna Commission completed the Pacific bluefin stock assessment in March at Southwest Fisheries Science Center (SWFSC) in La Jolla, California, USA.

The stock assessment indicates that the size of the Pacific bluefin spawning stock in 2014 was only 2.6% of its “unfished” size in 2014, compared to 2.0% in 2012. This represents a potential increase in the stock biomass from 2012 to 2014.

The unfished biomass level is the current amount of fish in the population compared to the amount if fishing had not occurred at all. The spawning biomass is the amount of fish that are reproductively mature.

It does not include the immature (or juvenile) fish, which are the only bluefin found by researchers in the Eastern Pacific Ocean feeding grounds. ISC scientists also determined that the recruitment, or the survival level of young fish, has been historically low the past three years, but not the lowest ever.

The previous Pacific bluefin stock assessment (in 2014) concluded that there was 4.2% of the unfished spawning biomass in 2012. The decline from 4.2% (2014 assessment) to 2.0% (2016 assessment) is not due to a decline in the population. It represents an enhancement in the model and an overall downward shift in the numbers of fish in the last 30 years.

The results of the 2016 assessment did not reflect the impact of the more restrictive management measures adopted in 2014 because they were implemented for 2015 and 2016. Data from 2015 and 2016 will be considered in the next assessment.

However, the assessment projected the impact of existing and hypothetical management measures on the status of the stock as of 2014. They indicate that the management measures implemented in 2015 and 2016 are likely to achieve the Western and Central Pacific Fisheries Commission’s (WCPFC) interim target for rebuilding the stock, under average recruitment scenarios. Experts have not yet determined the amount that would indicate the population is recovered.

The results are available for the WCPFC, IATTC, and the Pacific Fishery Management Council to use in establishing updated management measures and recovery plans.

source: Southwest Fisheries Science Center