Demographic and risk analyses applied to management and conservation of the blue shark (Prionace glauca) in the North Atlantic Ocean

Abstract

Management and conservation of the North Atlantic blue shark are handicapped by a fishery-data-limited stock-assessment process. The status of this stock is ambiguous at a time when catch appears to be on the rise and new trade and exploitation patterns are emerging. This research provides fishery-independent demographic and risk analysis results for use in conservation and management. An age-structured matrix population model in which the vital rates are stochastic was constructed. A mean finite rate of population increase (λ) of 1.23 year–1 and a mean population doubling time (t2) of 3.08 years suggests that the blue shark is one of the most productive shark species. However, this concept of high productivity could be misleading because an elasticity analysis shows a strong dependence of the population growth rate on the survival of juveniles (0–4 years). An analysis of the risk that the harvested population will decline to levels below an assumed threshold of 50% of pre-exploited levels was conducted. The risk analysis is proposed as a supplement to the data-limited stock assessment, to better evaluate the probability that a given management strategy will put the population at risk of decline.