Evaluating fishery impacts: Application to bigeye tuna (Thunnus obesus) in the eastern Pacific Ocean

The use of fishery impact plots and maximum sustainable yield estimations by fishery to evaluate fishery impacts are illustrated using the bigeye tuna stock assessment in the eastern Pacific Ocean (EPO). The stock status of the bigeye tuna stock in the EPO is evaluated using the general stock assessment model Stock Synthesis II. Fishery impact plots are developed to examine the effects of the different fishery groups on the bigeye tuna spawning biomass by simulating the population dynamics while removing each fishery. Maximum sustainable yields and associated quantities are calculated using the selectivity of each fishery group. Historically, the longline fleets have had the greatest impact on the stock of bigeye tuna, but since about 1993 the purse-seine fleet has increased its impact, and its catches and effect on the stock are currently greater than those of the longline fishery. However, the theoretical long-term yields obtainable from a purse-seine fishery are much less than those obtainable from a longline fishery.