Intense fishing for bluefin tunaThunnus thynnusin the western Atlantic Ocean began in the 1960s, when landings peaked at nearly 20,000 metric tons (mt). During the 1970s, landings averaged about 5,000 mt. The International Commission for the Conservation of Atlantic Tunas (ICCAT) established a total allowable catch (TAC) of 1,160 mt in 1982 and has set limits ranging from 1,995 to 2,660 mt annually since. The Commission's assessments indicate that unrestricted fishing through the 1960s and 1970s resulted in a sharp decline in abundance, primarily because heavy fishing on young fish wasted potentially good recruitment. Since the late 1980s, ICCAT management has stabilized the western Atlantic population, and recently there are signs of improvement. Resource assessments and management of western Atlantic bluefin tuna are subjects of severe controversy. Two of the most controversial issues are the stock assessment implications of fish migrations between the western and eastern Atlantic management units and the strategies for rebuilding abundance in the western Atlantic. In 1994, the U.S. National Research Council (NRC) was commissioned to review bluefin tuna stock assessments with particular emphasis on the issue of population mixing. The NRC report was widely misinterpreted as being more optimistic than it really was for the western population. Analyses by the NRC committee indicated that the abundance of spawning age fish in the west was higher than the value estimated in the 1993 ICCAT assessment but also that recruitment in the western Atlantic had failed so badly that some year-classes were estimated to have zero fish. Projections of future population size based on the NRC analyses indicated that recent levels of catch could not have been sustained. The critical issue now facing fishery managers is how to rebuild the population to a size, estimated to be about eight times the current size, that can produce maximum sustainable yield. One strategy (referred to as “active”) is to reduce the fishing mortality, which would permit some immediate rebuilding and enhance the likelihood of better recruitment in the future. Another strategy (referred to as “passive”) is to wait for natural variability in recruitment to bring a fortuitously strong year-class that would be invested in rebuilding, rather than in harvest. The most recent ICCAT assessment evaluated rebuilding strategies, but the method used has limitations that should be understood before decisions about rebuilding are made.