Stock Status of Pacific Bluefin

The International Scientific Committee for Tuna and Tuna-like Species in the North Pacific (ISC) last assessed the stock status of Pacific bluefin tuna in 2008. There is only one stock of Pacific bluefin tuna so the assessment looked at the entire population basin-wide. ISC scientists and Pacific fishing nations have made significant strides in data collection and anaylsis since the last stock assessment in 2004, and the 2008 assessment was the first to make a quantitative estimate of abundance with some degree of confidence.

Adult population size, known as spawning stock biomass, fluctuated widely over the 50 years of data examined in the assessment (1952-2005, see Figure 1 below). Likewise, catch in both the western and eastern Pacific was widely variable and showed no significant trend (Figure 2). 2005 biomass is near the median level over the assessment period.  There are no fishing mortality target levels for Pacific bluefin tuna, but current fishing mortality is higher than both Fmax and Fmsy, two commonly used catch rate goals. Of particular concern is the fact that the catch in weight is dominated by small fish (ages 0-3).

If fishing mortality remains the same and environmental conditions continue to be favorable, the assessment predicts that biomass will either decline until 2010 or remain at approximately the current level.  The scientists caution against an increase in fishing mortality and note that a decrease should lead to greater sustained yield in the future.

NOAA Fisheries classifies the overfished and overfishing status of Pacific bluefin as unknown.

Figure 1. Adult population size of Pacific bluefin tuna from 1952-2005 (ISC 2008).

Figure 2. Pacific bluefin tuna landings from 1952-2006. Although catch is highly variable, eastern Pacific landings are consistently lower than in the western Pacific.