# Habitat‐Based Predictions of Bridle Shiner (Notropis bifrenatus) in the Northeastern United States

## TL;DR

This study models bridle shiner habitats in Maine and New Hampshire to guide conservation efforts and identify suitable areas for surveys or reintroduction.

## Contribution

The study provides novel local and regional models of bridle shiner habitat associations and quantifies historical habitat loss in Maine and New Hampshire.

## Key findings

- Bridle shiners are associated with submerged vegetation, organic substrate, and watermilfoil at local sites.
- Ensemble SDMs link bridle shiner presence to forested regions, sand substrate, and low-elevation terrain.
- Fine-scale models indicate a 36% habitat loss in Maine and 16% in New Hampshire since historical times.

## Abstract

We sought to assess bridle shiner (
Notropis bifrenatus
) habitat associations at local and regional scales across southern Maine and New Hampshire. We used local habitat data at 95 Maine sites to predict occupancy with classification and regression trees (CART). We then used ensemble species distribution models (SDMs) to model the historical (1898–2008) and current (2009–2022) ranges of the species. We used the BIOMOD platform to model the association between 35 environmental variables and bridle shiner presence during both time periods and at fine (pseudo‐HUC14) and coarse (HUC12) spatial scales. We then calculated the change in predicted occupied drainages to estimate the change in the species' distribution at both scales. Within a site, bridle shiners were associated with submerged aquatic vegetation, organic substrate, and watermilfoil (Myriophyllum spp.). SDMs revealed an association with Appalachian (Hemlock‐)Northern Hardwood Forest, sand substrate, and low‐elevation terrain (at both spatial scales). Ensemble fine‐scale SDMs suggest a substantial loss of historical bridle shiner habitat in both Maine (36% of drainages) and New Hampshire (16%), with comparable described losses (of 21% and 14%) at a coarse scale. Our local and regional models may be used to focus surveys on areas with high predicted habitat suitability or to inform habitat restoration efforts.

We developed local and regional models for Maine and New Hampshire that may be used to focus bridle shiner (
Notropis bifrenatus
) surveys on areas with high predicted habitat suitability. This is significant because bridle shiners receive protection or concern status in thirteen states and two Canadian provinces: Limited data show that bridle shiners have declined dramatically throughout most of the species' native range, and our results provide evidence that bridle shiners are declining in Maine and New Hampshire. In addition to guiding the search for undiscovered populations of bridle shiner, managers may also use our model results to search for suitable reintroduction sites or focus habitat restoration efforts.