Using multistate occupancy estimation to model habitat use in difficult-to-sample watersheds: bridle shiner in a low-gradient swampy stream

We used multiseason, multistate patch occupancy models to investigate habitat use of a regionally rare minnow (bridle shiner, Notropis bifrenatus) within a difficult-to-sample, swampy stream system by defining occupancy states as coarse abundance categories (i.e., none, some, many). Habitat patches were repeatedly subsampled during three sampling periods spanning June to August 2011 using a nonstandard purse-and-lift method with a seine net, as poorly defined shorelines, unconsolidated substrate, and emergent vegetation limited beaching and restricted possible sampling locations. Detection probabilities increased from June to August, likely due to increasing catch per effort as age 0 became vulnerable to the gear, supported by the probability of detection being greater when the species was at high abundance, given occupancy. The probability of a habitat patch being occupied increased with the percent of macrophyte cover and decreased with increasing distance from another occupied patch. Decreasing mean depth showed a weak relationship to high abundance, given a patch was occupied. In summary, the multistate occupancy analytical approach was highly informative for developing quantitative habitat relationships and was seen as an effective framework for evaluating habitat use of aquatic organisms that inhabit environments inherently difficult to sample for which imperfect detection and sampling efficiency are of concern.