RISK FACTORS AFFECTING THE VAQUITA (PHOCOENA SINUS)1

Authors

  • Lorenzo Rojas-Bracho,

    1. Facultad de Ciencias Marinas, Universidad Autónoma de Baja California (UABC)/Programa Nacional de Mamíferos Marinos, Instituto Nacional de la Pesca (INP), Km 103 Carretera Tijuana-Ensenda, Ensenada 22800, Baja California, Mexico
    2. Southwest Fisheries Science Center, P. O. Box 271, La Jolla, California 92038-0271, U. S. A. E-mail: Irojas@ucsd.edu
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  • Barbara L. Taylor

    1. Southwest Fisheries Science Center, P. O. Box 271, La Jolla, California 92038-0271, U. S. A.
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  • 1

    Although we never enjoyed the privilege of working with Ken Norris, it is hard to imagine a marine mammalogist who has not been influenced by his work directly or indirectly. His influence is especially strong for those of us working with the vaquita. In 1958 mammalogists world-wide were able to read the description of a new species of porpoise from the Gulf of California (Norris and MFarland hypothesized that speciation occurred through isolation in the Upper Gulf of California. These views are still accepted today. These examples illustrate Ken Norris extraordinary understanding of natural history and biological processes. Ken kept his interest in vaquita biology and conservation his entire life and published other papers about the species. To the pioneer that Ken Norris was in the conservation of marine mammals, particularly in the case of the vaquita, we dedicate this paper about the conservation of this endemic porpoise from the Upper Gulf of California.

Abstract

Despite the vaquita being commonly cited as one of the most endangered marine mammals in the world, there is still disagreement over which factors put the species at greatest risk of extinction. This lack of agreement hinders management decisions needed to reduce the risk to the species. To expedite decision-making we consider four major risk factors. Habitat alteration from reduced flow of the Colorado River does not currently appear to be a risk factor because productivity remains high in vaquita habitat. Pollutant loads are low and pose low to no risk. Reduced fitness from inbreeding depression and loss of genetic variability are unlikely to pose high risk currently, though risk will increase if vaquitas remain at low abundance over long periods of time. Mortality resulting from fisheries bycatch poses high risk. Thus, short term management should not be hindered by uncertainty in estimating the risk of these factors, and primary conservation efforts should be directed to wards immediate elimination of incidental fishery mortality.

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