Populations of bluefin tuna, already on the decline worldwide due to overfishing, are likely to continue to plummet after international management body ICCAT failed to adopt stricter fishing quotas for the upcoming year. The results of last weekend's meeting brought condemnation from conservation groups, and scientists warn that limits twice the species' ability to repopulate may lead to a collapse of commercial tuna fishing and a population level that will never rebound.

Atlantic bluefin tuna populations have decreased by 80 percent or more since 1970. However, legal tuna fishing limits for 2008 will once again be around 29,000 tonnes, nearly twice the 15,000-tonne sustainable rate determined by advisory scientists of ICCAT (the International Commission for the Conservation of Atlantic Tuna). And that limit doesn't account for extensive illegal and unreported fishing, which may add another 50 percent in excess of official catch quotas.

The falling population of bluefin tuna is not only a threat to a majestic species--the fish routinely grow longer and heavier than an adult human--but a symptom of a larger global fisheries crisis. Seventy-five percent of commercially important marine fish populations are being fished beyond their biological limit, and the strain on oceans is increasing with growing world population and globalization's greater trade flows.

The Promise, and Problems, of Aquaculture

Aquaculture is to thank for fish production keeping pace with growing demand, even as ocean capture has leveled off since the late 1980s. Aquaculture, the practice of raising fish and other marine organisms in captivity, now accounts for nearly one-third of global fish production. As an alternative to overfishing natural marine ecosystems, the growing aquaculture business is a positive trend in fisheries.

However, aquaculture presents problems of its own. In the case of bluefin tuna ranching, the fish are caught when they're small and raised in sea cages, and are often killed before they can reproduce. Capture of smaller fish as feed for captive tuna puts further strain on wild populations such as anchovies and mackerels.

Furthermore, capture of small feed fish is accompanied by bycatch, or incidental capture of non-target species. Many times the unwanted bycatch dies and is simply dumped overboard, wasting valuable food supplies. In other instances, bycatch may be made into feed for aquaculture operations. However, bycatch species are frequently a food source for coastal areas, such as western Africa, where fish is a substantial part of dietary protein. Depletion of these species, indirectly furthered by aquaculture, is a problem for smaller subsistence fishermen, who don't have equipment or boats to pursue fish to more remote locations as commercial fishing vessels do.

Nutritional Importance of Fish

Source: Fishing for Answers, WRI 2004

Managing Oceans as Ecosystems

Though global trade has kept fish on the plates of developed nations, subsistence fishermen have likely been most affected by worldwide fisheries decline so far. And the decline continues as commercial fisheries respond by expanding their geographic scope and intensifying fishing in existing areas (see map).

The future health of our oceans demands rethinking business as usual. The first step toward a solution is to consider oceans as ecosystems rather than food barrels, a view that has been gaining ground within fisheries management. An ecosystem approach takes into account not just one target species, but its interaction with other species and with the physical marine environment, to better set limits and develop practices. A solution should also address:

• reducing fishing vessels on the water and cutting large government subsidies for fishing industry
• tougher quotas and more reliable enforcement by governments
• creation of large marine protected areas, which are currently far less numerous than protected land areas

RELATED LINKS

National Geographic feature: Still Waters: The Global Fish Crisis

Animated map of global fisheries

Monterey Bay Aquarium's Seafood Watch helps you make seafood choices that are good for the oceans.

EarthTrends

Farming Fish: The Aquaculture Boom

The Impact of Global Trawling: Mapping Our Footprint on the Seafloor

Global Map of Fisheries Peak and Decline

Ask EarthTrends: Where can I find information about aquaculture and its environmental impact?

Top photo by kidcadaver on Flickr