Over-wintering of brook trout: A look at fish movement, fish condition and assessment of habitat

 Sevenmile Creek, in Michigan’s Upper Peninsula, was studied for two winters to examine the effect of winter conditions on brook trout (Salvelinus fontinalis) and their habitat.  We electrofished to capture brook trout and assess fish condition (Fulton’s Factor).  During winter 1 there was a steady decline in condition for both 1+ age fish (18.6%) and 0+ age fish (6.2%) from November to March, with a sharp increase in April (4.8% and 7.1% respectively), coinciding with the spring breakup period.  Drift samples were collected to determine if the abundance/diversity of aquatic invertebrates plays a role in fish condition.  Habitat assessment from winter 1 showed that surface ice formation (both thickness and extent) is critical in habitat alteration, as stream velocity and stream depth varied dramatically during the winter.  For example, one riffle transect’s mean velocity decreased 24.2% while a run transect’s mean velocity increased 33.4%, during the same period.  Brook trout (18) were also implanted with radio tags to determine overwinter habitat occupation following the post-spawn period.  While some fish moved considerable distances (>1 km), others showed little movement.  This data shows the importance of future studies of brook trout conservation during the cold-weather months.