Introduced northern pike predation on salmonids in southcentral Alaska

• Published in: Ecology of Freshwater Fish
• Main Authors: Sepulveda, Adam J., Rutz, David S., Ivey, Sam S., Dunker, Kristine J., Gross, Jackson A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2013
• Subjects: Northern pike; Alaska; Slimy sculpin
• Online Access: http://dx.doi.org/10.1111/eff.12024; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Feff.12024; https://onlinelibrary.wiley.com/doi/pdf/10.1111/eff.12024

Abstract Northern pike ( E sox lucius ) are opportunistic predators that can switch to alternative prey species after preferred prey have declined. This trophic adaptability allows invasive pike to have negative effects on aquatic food webs. In Southcentral Alaska, invasive pike are a substantial concern because they have spread to important spawning and rearing habitat for salmonids and are hypothesised to be responsible for recent salmonid declines. We described the relative importance of salmonids and other prey species to pike diets in the Deshka River and Alexander Creek in Southcentral Alaska. Salmonids were once abundant in both rivers, but they are now rare in Alexander Creek. In the Deshka River, we found that juvenile Chinook salmon ( O ncorhynchus tshawytscha ) and coho salmon ( O . kisutch ) dominated pike diets and that small pike consumed more of these salmonids than large pike. In Alexander Creek, pike diets reflected the distribution of spawning salmonids, which decrease with distance upstream. Although salmonids dominated pike diets in the lowest reach of the stream, Arctic lamprey ( L ampetra camtschatica ) and slimy sculpin ( C ottus cognatus ) dominated pike diets in the middle and upper reaches. In both rivers, pike density did not influence diet and pike consumed smaller prey items than predicted by their gape‐width. Our data suggest that (1) juvenile salmonids are a dominant prey item for pike, (2) small pike are the primary consumers of juvenile salmonids and (3) pike consume other native fish species when juvenile salmonids are less abundant. Implications of this trophic adaptability are that invasive pike can continue to increase while driving multiple species to low abundance.