Landscape‐Scale Evaluation of Asymmetric Interactions between Brown Trout and Brook Trout Using Two‐Species Occupancy Models

Abstract

Predicting the distribution of native stream fishes is fundamental to the management and conservation of many species. Modeling species distributions often consists of quantifying relationships between species occurrence and abundance data at known locations with environmental data at those locations. However, it is well documented that native stream fish distributions can be altered as a result of asymmetric interactions between dominant exotic and subordinate native species. For example, the naturalized exotic Brown Trout Salmo trutta has been identified as a threat to native Brook Trout Salvelinus fontinalis in the eastern United States. To evaluate large‐scale patterns of co‐occurrence and to quantify the potential effects of Brown Trout presence on Brook Trout occupancy, we used data from 624 stream sites to fit two‐species occupancy models. These models assumed that asymmetric interactions occurred between the two species. In addition, we examined natural and anthropogenic landscape characteristics we hypothesized would be important predictors of occurrence of both species. Estimated occupancy for Brook Trout, from a co‐occurrence model with no landscape covariates, at sites with Brown Trout present was substantially lower than sites where Brown Trout were absent. We also observed opposing patterns for Brook and Brown Trout occurrence in relation to percentage forest, impervious surface, and agriculture within the network catchment. Our results are consistent with other studies and suggest that alterations to the landscape, and specifically the transition from a forested catchment to one that contains impervious surface or agriculture, reduces the occurrence probability of wild Brook Trout. Our results, however, also suggest that the presence of Brown Trout results in lower occurrence probability of Brook Trout over a range of anthropogenic landscape characteristics, compared with streams where Brown Trout were absent.

Evaluating the Trade‐Offs between Invasion and Isolation for Native Brook Trout and Nonnative Brown Trout in Pennsylvania Streams

“…Our findings are consistent with the results of these previous studies in that the first PCA axis revealed that Brook Trout are associated with smaller streams at higher elevations (Table ), which often have more forest cover and colder instream temperatures (Wagner et al. ; DeWeber and Wagner ; Kanno et al. ).…”

“…; Wagner et al. ), and maintaining groundwater upwelling zones that create thermal refugia (Hitt et al. ).…”

“…; Wagner et al. ). It is also well documented that Brown Trout have pronounced negative impacts on both native trout and native nongame species, with Brown Trout being listed as one of the 30 most globally invasive fish species (reviewed in Budy and Gaeta ; see also McDowall ; Kirk et al.…”

Conservation planning at the intersection of landscape and climate change: brook trout in the Chesapeake Bay watershed

“…, Wagner et al. ). Imperfect detection can affect model inferences and result in biased distribution estimates (Lahoz‐Monfort et al.…”

“…Introduction and establishment of non‐native salmonids (i.e., rainbow and brown trout) is further altering large‐scale brook trout distributions within the Chesapeake Bay watershed (Wagner et al. ).…”