Management of the sandbar shark, Carcharhinus plumbeus: implications of a stage-based model
Brewster-Geisz, K.K.; Miller, T.J. (2000). Management of the sandbar shark, Carcharhinus plumbeus: implications of a stage-based model. Fish. Bull. 98(2): 236-249
In: Fishery Bulletin. US Government Printing Office: Washington, D.C.. ISSN 0090-0656; e-ISSN 1937-4518, more
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Carcharhinus plumbeus (Nardo, 1827) [WoRMS]
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| Authors | | Top |
- Brewster-Geisz, K.K.
- Miller, T.J.
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| Abstract |
Sandbar sharks (Carcharhinus plumbeus) support an important commercial fishery. They are managed as a component of a multispecies group, termed large coastal sharks, by the National Marine Fisheries Service (NMFS) under the Fishery Management Plan (FMP) for Atlantic sharks. Currently, large coastal sharks, generally, and sandbar sharks, specifically, are considered overfished. Several management options, including nursery ground closures and size limits, are being considered to conserve the fishery. We explored the implications of management options for large coastal sharks within the framework of a stage-based model. Based on biological criteria, the life cycle of the sandbar shark was represented as five stages: neonate, juvenile, subadult, pregnant adults, and resting adults. The model followed only females. From a fishing mortality rate (F) of 0.20, estimated in the 1996 stock evaluation workshop (SEW), the model projects a population decline to 13 % of its current abundance within 20 years. The population is not stabilized until F is reduced to 0.07. In one run of the model, we assumed that F on neonates and pregnant adults was zero in order to assess the impact of a "perfect" nursery ground closure. Under this scenario, the population continued to decline unless F on the remaining stages was reduced to 0.097. Even with the closure of nursery grounds or the introduction of size limits to protect neonates and juveniles, F has to be reduced substantially. The model is highly sensitive to the dynamics of juveniles and subadults, which implies that management should protect these immature sharks to rebuild the stock. |
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