Bluefin tuna are assessed and managed as two distinct stocks by the International Commission for the Conservation of Atlantic Tunas with the management boundary approximately at the 45º west meridian. The current assessments and management strategies assume no mixing. However, there is extensive evidence that these two spawning populations of bluefin tuna exhibit spatial overlap in their distributions and mixing across the management boundary. Stock mixing is recognized as a major source of uncertainty in informing Atlantic bluefin tuna fisheries management strategies and annual catch advice. Simulation testing of alternative assessment models and management strategies is needed to understand the implications of stock mixing and uncertainty in Atlantic bluefin tuna life history.
Our research addresses this need through Management Strategy Evaluation (MSE). MSE is considered the state-of-the-art for developing and testing the performance and robustness of fisheries policy and strategic management advice. The approach involves building a model to simulate the population dynamics and movement of Atlantic bluefin tuna, as well as harvest by the fishery, wherein the simulated status of the resource triggers action based on management strategies, and subsequent management decisions in-turn affect fishing activities and feedback on the resource.
The objectives of this work are to: 1) develop operating models that represent stock structure and mixing of Atlantic bluefin tuna, 2) apply alternative stock assessment models and compare model performance, 3) develop biological reference points for bluefin tuna that incorporate the influence of mixing, and 4) test alternative management strategies against the goal of sustainability of eastern and western spawning populations and consider the impact exploitation of each stock has on the other.