| Abstrakt: |
AbstractLike many fishes native to western Great Plains streams, the Arkansas darter Etheostoma craginihas declined, apparently in response to changes in flow regimes and habitat fragmentation. We investigated the effectiveness of translocation as a management strategy to conserve this threatened species in the Arkansas River basin of southeastern Colorado. We used a multiscale design to sample the darter and several attributes of its habitat at the local 10-m site scale, the 3.25-km translocation segment scale, and the 10-km riverscape scale in all 19 streams where it had been previously translocated. The darter was captured in 11 of the 19 streams, although 5 were completely dry when visited. Arkansas darters had reproduced in 10 of the 11 streams (one criterion in the state recovery plan), and 6 streams also met a second criterion for abundance (>500 individuals). However, the populations in only two streams unequivocally met a third criterion of being self-sustaining, because the other four streams had been stocked annually with hatchery-reared Arkansas darters. We used multistate occupancy estimation, based on two consecutive dipnetting surveys, to determine the habitat characteristics correlated with site occupancy and the detectability of Arkansas darters at the local site scale. The probability of detection for the darter at occupied sites was high for both age-groups, 92% for age-0 darters and 75% for age-1 darters, and was a function of day of year (age 0) and habitat depth (age 1). Cool stream temperature (a site-scale variable) and sufficient length of available habitat (a riverscape-scale variable) were the strongest predictors of site occupancy for both age-groups. The models are useful in identifying new sites for translocations and factors that may place current populations at risk. Effective conservation will require land management practices that conserve, protect, and restore contiguous stream segments with cool temperatures that can sustain Arkansas darters.Received November 12, 2010; accepted December 13, 2011 |
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