Decline of the Shasta Crayfish (Pacifastacus fortis Faxon) of Northeastern California

Authors

  • Theo Light,

    1. Department of Conservation & Resource Studies, University of California at Berkeley, Berkeley, CA 94720, U.S.A.
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      Current address: Department of Wildlife, Fish, and Conservation Biology, University of California at Davis, Davis, CA 95616, U.S.A.

  • Don C. Erman,

    Corresponding author
    1. Department of Forestry & Resource Management, University of California at Berkeley, Berkeley, CA 92720, U.S.A., email dcerman@ucdavis.edu
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      Current address: Department of Wildlife, Fish, and Conservation Biology, University of California at Davis, Davis, CA 95616, U.S.A.

  • Chris Myrick,

    1. Department of Forestry & Resource Management, University of California at Berkeley, Berkeley, CA 92720, U.S.A., email dcerman@ucdavis.edu
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      Current address: Department of Wildlife, Fish, and Conservation Biology, University of California at Davis, Davis, CA 95616, U.S.A.

  • Jay Clarke

    1. Department of Conservation & Resource Studies, University of California at Berkeley, Berkeley, CA 94720, U.S.A.
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Address correspondence to Don C. Erman.

Abstract

Native freshwater faunas in North America are declining, principally due to the combined effects of habitat degradation and introduced species. Relatively little attention has been directed to the decline of freshwater invertebrates, which may be even more threatened than fishes. This paper chronicles recent changes in the distribution and abundance of the Shasta crayfish (Pacifastacus fortis Faxon), a state and federally endangered species endemic to the midreaches of the Pit River system in northeastern California. We made snorkeling and SCUBA surveys for crayfish in 1990 and 1991 and examined various records for historic distributions. Shasta crayfish have been extirpated from much of their historic range by water impoundment and diversion, and they are further threatened by two introduced crayfish species (Pacifastacus leniusculus Dana and Orconectes virilis Hagen). By 1990 Shasta crayfish were restricted to seven isolated populations, mostly in the headwaters of spring-fed tributaries to the Pit river. P. leniusculus had become established throughout much of the study area in about 12 years. In one site P. leniusculus probably contributed to the precipitous decline of Shasta crayfish, from 2000–3000 in 1980 to about 370 (± 135) in 1991. O. virilis, which occurred in only the most disturbed parts of the system, showed little range expansion in 30 years and had been replaced in a large stretch of the Pit River by P. leniusculus. P. leniusculus occupied sites with a broad range of habitat variables (temperature, pH, turbidity, substrate size) partly or wholly overlapping measures of sites with the other two species. The decline of the Shasta crayfish, like the extinction of its closest relative P. nigrescens in the San Francisco Bay area earlier this century, reflects the decline of its habitat and probably pressure from the aggressive exotic P. leniusculus.

Abstract

La fauna nativa de agua dulce en Norteamérica está declinando, principalmente debido a los efectos combinados de la degradación del hábitat y de las especies introducidas. Se ha puesto relatívamente poca atención en la declinación de los invertebrados de agua dulce, los cuales podrían estar más amenazados que los peces. Este trabajo detalla cambios recientes en la distribución y abundancia del cangrejo de río de Shasta (Pacifastacus fortis Faxon), una especie considerada en peligro tanto a nivel estatal como a nivel federal y que es endémica del sistema del río Pit en el noreste de California. Llevamos a cabo evaluaciones de los cangrejos de agua dulce usando snorkel y SCUBA en 1990 y 1991 y examinamos varios registros de distribuciones históricas. El cangrejo de Shasta ha sido extirpado de la mayor parte de su área de distribución histórica por el embalse y desvio de las corrientes de agua; ademas esta amenazado por dos species de cangrejo introducidas (Pacifastacus leniusculus Dana y Orconectes virilis Hagen). Hacia 1990 el cangrejo de Shasta estaba restringido a 7 poblaciones aisladas, la mayoría de ellas en las cabeceras de los tributarios del río Pit. P. leniusculus se ha establecido a lo largo de la mayor parte del área de estudio en aproximadamente 12 años. En un sitio, P. leniusculus contribuyó probablemente a la declinación precipitada del cangrejo de Shasta, que decreció de 2000–3000 en 1980 a 370 (±135) en 1991. O. virilis, que se encontró sólo en las partes más pertubadas del sistema, mostró una pequeña expansión en su área de distribución en 30 años y ha sido reemplazado, en gran parte del río Pit, por P. leniusculus. P. leniusculus ocupó sitios con un amplio rango en las variables del hábitat (temperatura, Ph, turbidez, tamaño del sustrato), superponiéndose en forma parcial o total con las medidas de los sitios que poseían las otras dos especies. La declinación del cangrejo de Shasta, al igual que la extinción de su pariente más cercano P. nigrescens en el área de la Bahía de San Francisco, que ocurrió tiempo atrás durante este siglo, refleja la declinación de este hábitat y probablemente la presión de la especie exótica y agresiva P. leniusculus.

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