| Abstrakt: |
A repatriation program to conserve critically imperiled razorback sucker Xyrauchen texanus, an endemic fish of the Colorado River basin in western North America, was initiated in 1990. The species, once widespread and abundant, now is extirpated from most of its range because of human-induced factors. Natural recruitment to wild populations rangewide is largely precluded by nonnative predation. The largest remaining wild population occurs in Lake Mohave, Arizona and Nevada, but its numbers have declined dramatically over the past decade, such that the genetic legacy of the species may soon be lost. As part of a cooperative repatriation program, more than 440,000 naturally produced razorback sucker larvae were harvested and grown in protective custody; from these, nearly 58,000 marked juveniles were released into the lake between 1993 and 2002. Annual repatriate population estimates (modified Petersen method) ranged from 1,017 to 2,494 and poststocking survivorship (Program MARK) ranged from 2% to 6% for the period 19992002. Total length at release was the most important determinant of poststocking survival, which more than doubles for releases averaging 350 mm compared with those averaging 300 ram. Achieving the program goal of reestablishing an adult population of 50,000 individuals depends upon increasing repatriate survival. [ABSTRACT FROM AUTHOR] |
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