Bluefin Tuna Stock Assessments

The Atlantic bluefin tuna is one of the ocean's most remarkable fish. Weighing up to 700 kg (1,500 lbs) and able to dive to deeper than 1,000 m (3,000 ft), these animals travel up to 64 km per hour (40 mph) as they crisscross the Atlantic Ocean in a 7,000 km (4,800 mi) migration. As one of only a few warm-blooded fish species, bluefin tuna are able to elevate their body temperature as they move through a wide range of conditions.

These fish are one of the world's most valuable marine species. Unreported and illegal fishing, spurred by a growing demand for sushi, pushed this once-plentiful species to the brink of collapse. Atlantic bluefin tuna now face a long road to recovery, as both eastern and western populations have been fished to near-historic lows.

The International Commission for the Conservation of Atlantic Tunas (ICCAT), the body responsible for the management of Atlantic bluefin, uses information from stock assessments, conducted every two to three years, to set conservation and management measures and yearly catch limits, or quotas. Precautionary catch limits, which allow the population to rebuild after years of overfishing, are critical for Atlantic bluefin tuna's recovery. The scientific assessments of these fish are conducted by the Standing Committee on Research and Statistics (SCRS), a panel of scientists from ICCAT member countries. These assessments provide information to decision makers on the current status and size of Atlantic bluefin populations as well as predictions on how future management measures will affect the species.

How does a stock assessment work?

A stock assessment simulates the bluefin population as individual fish are born, grow up, reproduce, and die. To do this, scientists use computer models that incorporate mathematical formulas, statistical techniques, and data provided from a variety of sources. The results of these assessments are then considered by ICCAT as it sets catch limits, size restrictions, area closures, and other management and enforcement measures.

However, stock assessments are only as good as the data that are used. Many sources of information go into stock assessments, but catch records make up a significant portion of the data used. Atlantic bluefin catch records, however, are often inaccurate and lack crucial information, such as how old the fish were when caught. In addition, the amount of fish caught illegally is not accounted for, a factor that can skew the stock assessment, resulting in overly optimistic predictions. 

Improving the quality and quantity of data provided by both fishermen and scientists for the bluefin assessments will allow ICCAT to make more-informed decisions to protect this important species and help it recover.