Winter can be a stressful period for stream-dwelling salmonid populations, often resulting in reduced growth and survival. Stream water temperatures have been identified as a primary mechanism driving reductions in fitness during winter. However, groundwater inputs can moderate water temperature and may reduce winter severity. Additionally, seasonal reductions in prey availability may contribute to decreased growth and survival, although few studies have examined food webs supporting salmonids under winter conditions. This study employed diet, stable isotope, and mark-recapture techniques to examine winter (November through March) feeding, growth, and condition of brown trout Salmo trutta in a groundwater-dominated stream (Badger Creek, Minnesota, USA). Growth was greater for fish ≤ 150 mm (mean = 4.1 mg g-1 day-1) than for those 151-276 mm (mean = 1.0 mg g-1 day-1) during the winter season. Overall condition from early winter to late winter did not vary for fish ≤150 mm (mean relative weight (Wr) = 89.5) and increased for those 151-276 mm (mean Wr = 85.8 early and 89.4 late). Although composition varied both temporally and by individual, brown trout diets were dominated by aquatic invertebrates, primarily Amphipods, Dipterans, and Trichopterans. Stable isotope analysis supported the observations of the dominant prey taxa in stomach contents and indicated the winter food web was supported by a combination of allochthonous inputs and aquatic macrophytes. Brown trout in Badger Creek likely benefited from the thermal regime and increased prey abundance present in this groundwater-dominated stream during winter.
Bibliographical noteFunding Information:
*Corresponding author. Email: firstname.lastname@example.org fThe Unit is jointly sponsored by the US Geological Survey, the University of Minnesota, the Minnesota Department of Natural Resources, the US Fish and Wildlife Service, and the Wildlife Management Institute.
We thank the following for assistance in the field: Jane Mazack, Jenna McCullough, Jessica Miller, Lori Krider, Pat Sherman, Catherine DeGuire (University of Minnesota) and Dan Spence (MN DNR). We thank three anonymous reviewers for their beneficial comments on a previous version of this manuscript. All animals used in this study were handled according to animal use and care guidelines established by the University of Minnesota IACUC committee. Funding for this study was provided by Environment and Natural Resources Trust Fund administered by the Legislative Citizens Committee for Minnesota Resources, and the Kalamazoo Valley Chapter of Trout Unlimited. Any use of trade names is for descriptive purposes only and does not imply endorsement by the US Government.
- brown trout
- stable isotopes
- winter diet