Impacts of Northern Pike Predation on a Stocked Rainbow Trout Fishery

Establishment of Northern Pike in Pactola Reservoir, South Dakota has prompted concern among biologists about the influence of this species on the lake’s intensively managed salmonid fisheries.  Ancedotal information suggests that catch rates of Rainbow Trout have declined while mean size and abundance of Northern Pike has increased.  To quantify interactions between these species, we assessed size-dependent predation by Northern Pike on Rainbow Trout using bioenergetics modeling.  Stable isotopes combined with traditional diet analyses revealed that smaller Northern Pike (< 600 mm TL) consumed primarily centrarchids and Rainbow Smelt, with Rainbow Trout contributing less than 10% to their annual energy consumption.  In contrast, larger Northern Pike (≥ 600 mm TL) consumed primarily Rainbow Trout, that accounted for 56% of their annual energy consumption.  Combining estimates of Northern Pike predation with production costs of Rainbow Trout revealed that annual economic losses ranged from $15,259 to $24,801 USD per year.  Over its lifespan, an age-10 Northern Pike was estimated to consume ~117 Rainbow Trout worth approximately $340 USD.  Strategies for reducing the impact of Northern Pike predation on stocked Rainbow Trout include altering the size, timing, and spatial distribution as related to current trout stocking practices.