Demographic analysis of the impacts of fishing pressure on the Naru eagle ray Aetobatus narutobiei in Ariake Bay, Japan
摘要
Understanding how the endemic and threatened Naru eagle ray Aetobatus narutobiei responds to fishing mortality is fundamental for evaluating its population dynamics and developing sustainable management strategies. This species has been both targeted in a long-term predator control program and subjected to over two decades of intense fishing pressure in Ariake Bay. Using an age-structured demographic model, we evaluated current fishing pressure and conducted different fishing scenarios to assess population responses. Catch-at-age data indicated that recruitment to the fishery began at age 0, with juveniles of both sexes comprising the majority of the catch. The finite rate of population growth (λ) of 1.119 year−1 was estimated under unfished conditions based on the base model. However, after incorporating age-specific fishing mortality into the base model, λ markedly declined to 1.042 year−1 under the current condition, indicating that this species is highly sensitive to fishing pressure. Elasticity analysis further demonstrated that juvenile survival had the greatest relative influence on the population growth rate. Stochastic simulations incorporating life-history parameter uncertainty under scenarios of constant fishing mortality across age classes revealed that delaying the age at first capture to 6 years, thereby exceeding female age at maturity, could substantially reduce the risk of population decline under scenarios of increased fishing mortality.