Evaluation of the Razorback Sucker (Xyrauchen texanus) and Colorado Squawfish (Ptychocheilus lucius) reintroduction programs in central Arizona based on surveys of fish populations in the Salt and Verde rivers from 1986 to 1990

Abstract:

Between 1981 and 1990, more than 11 million hatchery-produced razorback suckers (Xyrauchen texanus) and 750,000 Colorado squawfish (Ptychocheilus lucius) were stocked to historic ranges in the Verde and Salt rivers in Arizona, where natural populations had been extirpated. Efforts to date have focused on broad-scale stockings and general fish surveys to evaluate success. Only 519 razorbacks and 444 squawfish were taken in several years of intensive electrofishing and netting surveys during all seasons throughout large segments of both rivers. Survival of razorbacks appears better in the upper Verde River than in the Salt River, while squawfish appear to fare better in the Salt River than do razorbacks. Most recaptures of either species were taken within weeks of stockings; relatively few individuals were verified to have lived more than a few months in the wild. Large populations of razor backs have not established in mainstreams, although groups have persisted in small, isolated, peripheral habitats where emigration is blocked or impeded. Despite growth to maturity of at least some razorbacks, no evidence of wild reproduction was found. The few squawfish known to have over-wintered in the wild were also taken from a habitat closed to downstream emigration. Proximate impediments to large-scale successful recruitment of stocked individuals to wild populations clearly include predation, principally by exotic flathead catfish and smallmouth bass, and coincident inability of hatcheries to produce large numbers of individuals for release at sizes large enough to escape predation. Despite limited success, it is recommended that stockings of both species continue for two reasons. Large-scale field experiments easily accomplished under the "experimental, non-essential" designation with readily available hatchery fish can elucidate mechanisms of recruitment failure for hatchery stock. These should emphasize experimental analyses of factors affecting mortality, movements and habitat use of stocked fish. Effects of fish condition, transport and stocking stress, size, stocking season, and parasites are other variables which need research. Along with experiments, continued stockings, especially in the case of razorbacks, even with low recruitment rates, appear very likely to contribute to establishment of long-lived populations, and are therefore recommended for both species. Stockings should be as extensive as possible, and focus on releases to closed, peripheral riverine and reservoir habitats (e .g. isolated backwaters), preferably with low or reduced predator populations. While direct stocking of larger individuals would likely increase survival rates in the wild, absolute numbers stocked would remain small given existing facilities . Stockings of far greater numbers of small individuals to such isolated, "wild" habitats and subsequent "wild" growth there prior to release, via either natural or artificial mechanisms, to larger, adjoining habitats, will likely prove to be the most economical and successful approach to establishing multiple, new populations oflong-lived individuals. Recommendations for immediate habitat management actions for both species include manipulations of predator populations and maximization of availability of backwater habitats. A broad-scale, annual field monitoring effort should continue, but most importantly the program should shift to emphasize experimental research. Effectiveness of the reintroduction program could be greatly improved by high-level administrative adjustments with particular attention to development of program objectives, coordination among production, research and monitoring components and frequent evaluation of progress toward objectives.

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