INTER-AMERICAN TROPICAL TUNA COMMISSION - Comisión ...

2.2. Tunas2.2.1. YellowfinThe yellowfin stock changed into a higher recruitment regime in about 1983, but may have recently moved back into an intermediaterecruitment regime. During 2005-2007, the yellowfin stock has been below the level corresponding to the maximum sustainableyield (27% of its unexploited size), but has increased to above that level in 2008. One estimate of the effect of this reduced stocksize is that the predation by adult yellowfin on other parts of the ecosystem is reduced to about 35% of what it was in the absence ofa fishery.2.2.2. SkipjackSkipjack assessments are far less certain than those for yellowfin and bigeye, in part because the fishery in the EPO does not appearto be having much impact on the stock. However, it appears that fluctuations in recruitment cause large variations in stock size.2.2.3. BigeyeUp to 1993, bigeye were taken mostly by longline fishing. The stock size in 1993 is estimated to have been 32% of its unexploitedsize. After 1993, purse seining for tunas associated with fish-aggregating devices (FADs) took significant quantities of small andmedium-sized bigeye. In 2005, after several years of poor recruitment and excessive levels of fishing mortality, the stock size wasestimated to be at about 14% of its unexploited size. Due to recent spikes in recruitment, the current level has slightly increased andstabilized at about 17%.2.2.4. Pacific bluefinIt is considered that there is a single stock of Pacific bluefin tuna in the Pacific Ocean, given that spawning apparently occurs only inthe western Pacific Ocean. However, tagging studies have shown that there is exchange of bluefin between the eastern and westernPacific Ocean. A preliminary stock assessment, carried out by the International Scientific Committee for Tuna and Tuna-like speciesin the North Pacific (ISC) in 2005, has indicated that the biomass of the spawning stock had local peaks during the early 1960s, late1970s, and late 1990s, with a decline after the last peak. It was previously hypothesized that a strong recruitment event that hadoccurred in 2001 would maintain spawning stock biomass above recent levels until 2010. Data collected more recently, however,indicate that the 2001 recruitment was not as strong as previously thought.2.2.5. AlbacoreIt is generally considered that there are two stocks of albacore in the Pacific Ocean, one in the North Pacific and the other in theSouth Pacific. An assessment for South Pacific albacore, done by the Secretariat of the Pacific Community in 2003, showed that theSouth Pacific stock was at about 60% of its unexploited size. An assessment by the ISC North Pacific Albacore Working Group in2006 indicated that the biomass of the North Pacific spawning stock in 2006 was about 53% above its time series average.2.3. Billfishes2.3.1. SwordfishThe northeastern and southeastern Pacific Ocean stocks of swordfish are distinctly identifiable by genetics and fisheries analyses.Preliminary analyses of the status of the southeastern Pacific Ocean stock of swordfish indicate that the spawning biomass declinedover the 1945-2003 period, and is now at about twice the level (~0.26) that will support the maximum sustainable yield (MSY)of 13,000-14,000 metric tons (t). Catches have been decreasing since about 2002. Recent harvests are on the order of 11,000 to13,000 t annually.The variations in standardized catch per unit of effort of swordfish in the northern EPO show no trend, suggesting that the catches todate have not affected the stock significantly.2.3.2. Blue marlinThere appears to be a single stock of blue marlin in the Pacific Ocean. The most recent stock assessments of blue marlin suggest thatthe current stock size is between 50 and 90% of the unexploited stock size.2.3.3. Striped marlinRecent genetics analyses suggest that there are three stocks of striped marlin in the north and eastern Pacific Ocean. Spawning areas113