International Seafood Sustainability Foundation

Posted by Victor R. Restrepo[1], Bruce B. Collette[2] and William W. Fox[3]
6 December 2011

A recent review of the status of tuna species (Collette et al.[4]), using data up to 2010 and applying the criteria set out by the International Union for Conservation of Nature (IUCN), found that management measures are working to protect some of the most heavily fished stocks, like albacore and bigeye. Stocks of skipjack are of “Least Concern” while bigeye tuna is Vulnerable due to overfishing in the western and central Pacific.

Highlights of the review include:

Least Concern

• Skipjack Tuna: This species is present in tropical waters of all oceans and is important in commercial fisheries throughout its range. Skipjack accounts for about 57% of the world’s catch of major tunas. Although it is heavily fished, it is considered abundant and is very resilient because it is fast-growing, short-lived, and very fecund. It is listed as Least Concern.

Near Threatened

• Albacore Tuna: This species is important in many commercial fisheries around the world, accounting for about 6% of the world’s catch of tunas.  The Indian Ocean, South Atlantic, and South Pacific stocks are being fished below current maximum sustainable yield (MSY).  Although the North Atlantic stock has been subject to overfishing in recent years, in 2009 catch quotas were adopted in line with scientific advice to end overfishing.  This species is listed as Near Threatened, primarily because population declines would be much greater if it were not for the catch quotas that have been implemented.

• Yellowfin Tuna: This species is fast-growing, widely distributed and highly productive. It is important in commercial fisheries around the world, accounting for over 25% of the world’s catch of tunas.  As of the time of the review, all stocks were being fished below current maximum sustainable yield (MSY). This species is listed as Near Threatened, primarily because population declines would be much greater if it were not for the catch quotas that have been implemented.

Vulnerable

• Bigeye Tuna: This species is important in commercial fisheries around the world, accounting for nearly 10% of the world’s catch of major tunas. It is being effectively managed throughout the majority of its range, with the exception of the Western and Central Pacific stock. All other stocks are being fished below current maximum sustainable yield (MSY). As the MSY of the Western and Central Pacific stock represents more than 20% of the global populations, this species is listed as Vulnerable globally.

Endangered and Critically Endangered

• Bluefin tunas are highly valuable but in volume they account for only about 1% of the world’s tuna catch. The Atlantic bluefin tuna is listed as Endangered, while southern bluefin is listed as Critically Endangered.  These populations were intensively fished in the past and there is no clear evidence that the abundance of the parental stocks is rebuilding. The population of Pacific bluefin is currently classified as Least Concern but a new stock assessment is needed.

In summary, skipjack, yellowfin and albacore, the three species that comprise a majority (89%) of the world’s commercial tuna catch, are not listed in the IUCN Threatened categories.

Unfortunately, some environmental advocates have been interpreting the IUCN listings incorrectly.   For example, when IUCN lists a fish as being in one of the three categories considered “Threatened,” it does not necessarily mean that the species is in immediate danger of extinction or collapse.   It just means that there has been a drop in the population size that meets the formula used in IUCN classifications and a closer look at the species is warranted. Fortunately, all the major populations of tunas, including bigeye, are watched closely and have frequent scientific assessments.

It’s important to note IUCN applies their formula to a broad range of land based and aquatic species. In other words, it’s a “one-size-fits-all” method. It’s not tailored to assess commercial fish species as ISSF and other scientists have noted previously and its application has some shortcomings when applied to commercial fisheries. The IUCN Red List looks at species globally and is meant to raise warning flags within a long-term time horizon. This list is not meant to be a replacement of the stock-specific stock assessments and management measures applied by the tuna Regional Fishery Management Organizations.

In the case of tunas, the conclusions of the IUCN review team are consistent with what the majority of fisheries scientists believe to be true:  that the longer-lived bluefin tunas are more vulnerable to overfishing, while bigeye, albacore, yellowfin and skipjack are more resilient to overfishing. Nevertheless, all fisheries need to be managed sustainably based on scientific analyses.

To learn more about the IUCN Red List, click here.