Connectivity Influences Translocation Success of Arkansas Darter in Fragmented Streams of the Western Great Plains: an Occupancy Sampling Approach

Like many fishes native to western Great Plains streams, the Arkansas darter Etheostoma cragini has declined, apparently in response to changes in flow regimes and habitat fragmentation. To increase the number of populations, darters were translocated into 19 streams and ditches, each fragmented to different degrees by road culverts and diversion structures. We analyzed the effects of several attributes of their habitat on translocation success at the riverscape and segment scales as well as those at local scales. We used multistate occupancy estimation, based on two consecutive dipnetting surveys, to determine habitat characteristics correlated with site occupancy and detectability of Arkansas darters. Darters were present in 11 of 19 streams, although 5 were completely dry when visited. 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, populations in only two streams unequivocally met the third criterion of being self-sustaining, because the other four streams had been stocked annually with hatchery-reared darters. Detectability of darters at sites where water was present was high for both age groups, 91% for age-0 darters and 76% for age-1 darters, and was a function of Julian date (age-0) and habitat depth (age-1). Residual stream temperature (a site-scale variable) and the total length of available habitat (a riverscape-scale variable) were the strongest predictors of site occupancy for both age groups. The models were useful in identifying fragmentation by a road culvert as a potential impediment to success in another stream where conservation biologists have proposed translocating darters. These models can be used to guide habitat conservation and land management practices that seek to conserve, protect, and restore current and future critical habitat for this threatened species in the Arkansas River basin.