The Highs and Lows of Rebuilding Western Atlantic Bluefin Tuna
The International Commission for the Conservation of Atlantic Tunas, or ICCAT, will meet in Cape Town, South Africa, from Nov. 18-25, to negotiate future catch limits for bluefin tuna fisheries in the western Atlantic Ocean. ICCAT scientists have recommended that current limits be maintained to allow the depleted bluefin population to grow and recover. However, some member governments are pushing for managers to ignore the scientific advice and increase the catch quota.
Watch the video below to learn why ICCAT needs to act with precaution and maintain current catch limits.
Much of the debate that surrounds catch limit negotiations for western Atlantic bluefin tuna is linked to the issue of recruitment, or the number of young fish added to the population each year. Several times a decade, ICCAT scientists perform a stock assessment for bluefin. These reports produce a picture of the current and future health of the population and provide advice to fishery managers on appropriate catch quotas. Estimates of recruitment are a fundamental part of these assessments. Unfortunately, the assessments are complicated by the uncertainty surrounding recruitment and the use of two recruitment hypotheses that produce contradictory sets of results.
Watch videos on the recruitment debate.
Under the high recruitment hypothesis, the number of young fish produced each year increases as the number of adult fish increases. Stock assessments that use this recruitment hypothesis find that the western Atlantic bluefin population is severely depleted and overfished. Under this hypothesis, maintaining the current catch quota would give the overfished western bluefin population a chance to recover and grow to a level five times larger than the current stock size. The majority of scientific data supports this hypothesis, and it is therefore the scenario used by scientists for most fish populations around the globe.
Low Recruitment Hypothesis
Under the low recruitment hypothesis, the number of young fish produced each year is capped by a set of hypothetical, but as-yet-undocumented environmental conditions. Under this hypothesis, even if the number of adult fish increases, the number of young fish would not exceed current levels. Stock assessments that use the low recruitment hypothesis show that the western Atlantic bluefin population is not overfished and not subject to overfishing. This scenario would allow for a modest increase in catch quotas with little or no effect on the next generation; the future population would remain about the same size as it is now. There is no scientific explanation or evidence of an environmental change.
The Road Map to Recovery
Most scientific evidence suggests that the bluefin tuna population in the western Atlantic could increase to a much greater size in the future, consistent with the high recruitment hypothesis, if current fishing levels are maintained. ICCAT scientists have recommended that catch limits should not be increased. Maintaining the current limits would allow the number of adult bluefin to increase and the population to grow. At the annual meeting in Cape Town, South Africa, ICCAT members should follow the scientific recommendations to cap the total catch at 1,750 metric tons for 2014 and 2015.