The Rise and Fall (Again) of the Porbeagle Shark Population in the Northwest Atlantic

Steven E. Campana*, Warren Joyce, Linda Marks, Peter Hurley, Lisa J. Natanson, Nancy E. Kohler, Christopher F. Jensen, Joseph J. Mello, Harold L. Pratt, Sigmund Myklevoll, Shelton Harley

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

29 Citations (Scopus)

Abstract

A comprehensive population dynamics analysis of porbeagle shark (Lamna nasus) in the Northwest Atlantic indicates that the population has collapsed for the second time in its 43-year fishing history. The virgin population in the early 1960s supported annual catches of over 9,000 metric tons (t) before the fishery collapsed in 1967. After a partial recovery over the next 25 years, annual catches of 1,000-2,000 t throughout the 1990s appear to have once again driven the population to record-low numbers. Both the size and the age composition of the catch have declined markedly since 1990, with relatively few large sharks left in the population. Commercial catch rates are now only 10-30% of those in the early 1990s. Both Petersen calculations based on tag recaptures and an age- and sexstructured population model suggest that recent biomass is 10-20% of that present in the virgin population. Porbeagle have a low pup production rate and mature considerably after the age at which they first appear in the fishery. In light of the very low numbers of mature females now found in the population, it is unlikely that even the strict quota management that has been implemented will allow the population to rebuild quickly. However, a 75% reduction in fishing mortality, accurate monitoring of catch, effort, and size composition, and area closures to protect mating aggregations have all been put into place to allow population recovery.

Original languageEnglish
Title of host publicationSharks of the Open Ocean
Subtitle of host publicationBiology, Fisheries and Conservation
PublisherWiley Blackwell
Pages445-461
Number of pages17
ISBN (Electronic)9781444302516
ISBN (Print)0632059958, 9780632059959
DOIs
Publication statusPublished - 30 Jan 2009

Bibliographical note

Publisher Copyright:
© 2008 by Blackwell Publishing Ltd. All rights reserved.

Other keywords

  • Lamna nasus
  • Overfishing
  • Population dynamics
  • Porbeagle
  • Stock abundance

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