Marine and Freshwater Research Marine and Freshwater Research Society
Advances in the aquatic sciences
RESEARCH ARTICLE

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

Alexandre M. Aires-da-Silva A B C and Vincent F. Gallucci A
+ Author Affiliations
- Author Affiliations

A School of Aquatic and Fishery Sciences, Box 355020, University of Washington, Seattle, WA 98195-5020, USA.

B Present address: Inter-American Tropical Tuna Commission, 8604 La Jolla Shores Drive, La Jolla, CA 92037-1508, USA.

C Corresponding author. Email: alexdasilva@iattc.org

Marine and Freshwater Research 58(6) 570-580 https://doi.org/10.1071/MF06156
Submitted: 1 September 2006  Accepted: 11 April 2007   Published: 29 June 2007

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.

Additional keywords: demography, shark fisheries management, Leslie matrix, nursery grounds.


Acknowledgements

The senior author was supported through doctoral grants by the Fulbright Commission and the ‘Fundação-Luso Americana para o Desenvolvimento’ (Project number 50/01) in Portugal, the School of Aquatic and Fishery Sciences (UW) scholarship fund and, the Wakefield Professorship endowment fund. We greatly appreciate the continuous support of John Hoey NOAA-NMFS. We appreciate the many discussions with Ian Taylor as well the other students in the UW shark research laboratory. We thank Greg Cailliet, André Punt and Jason Cope for critically evaluating a draft of this manuscript. We thank E. Cortés for sharing some of his latest work. We also thank one anonymous referee for his invaluable comments and suggestions.


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