Seasonal Movements and Mortality Instances of Brown Trout ( Salmo t rutta ) in a Black Hills Stream

Abstract

Brown Trout ( Salmo trutta ), a popular game fish in the Black Hills’ sport fishery, is poorly understood when it comes to seasonal movements in many Black Hills streams. We attempted to determine short and long-term movement patterns, seasonal movement changes (spawning and pre-winter), habitat preference and document mortality events across a 9-month period using radio telemetry. Twenty-five adult (227 - 421 mm) Brown Trout were surgically implanted with radio transmitters during the Summer of 2023. Movements throughout the study decreased throughout the period of sampling. Pre-spawning movements averaged 171 m in the short-term and 1,558 m over this phase. During the spawning period, movements decreased to 154 m short-term and 625 m long-term along with a further decrease post-spawn (20 m short-term, 310 m long-term). Habitat preferences during the pre-spawning (pools 23%, riffles 17%, runs 60%) and spawning season (pools 26%, riffles 12%, runs 63%) were different from those in the post-spawning season (pools 46%, riffles 5%, runs 49%), and three documented predation events occurred strictly during the post-spawning season. These findings give managers valuable insight towards seasonal movement patterns, habitat use and extent of predation on a wild Brown Trout fishery.