Stock Status of Pacific Bluefin Tuna

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. The ISC is now working diligently to improve catch data and determine key assessment model inputs such as natural mortality rate and maturation age in preparation for the next full assessment scheduled for 2012.

The 2008 assessment found that 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 is widely variable and shows 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 decline.  The scientists recommend that catch levels be reduced below the catch rates of 2002-04 and that catch of juveniles in particular should be decreased.

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 1952-2009. Although catch is highly variable, eastern Pacific landings are consistently lower than in the western Pacific.

 

Click here to download the 2008 ISC stock assessment report or the 2010 ISC data preparatory report. Additional information on fishery and population status for Pacific bluefin tuna is available in the following reports:

» Status of the U.S. West Coast Fisheries for HMS Through 2009 (Pacific Fishery Management Council, 2010)
» Status of Bluefin Tuna in the Pacific Ocean (Inter-American Tropical Tuna Commission, 2001)