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Division: Sport Fish
Title: Alexander Creek northern pike suppression.
Author: Rutz, D., P. Bradley, C. Jacobson, and K. Dunker.
Year: 2020
Report ID: Alaska Department of Fish and Game, Fishery Data Series No. 20-17, Anchorage.
Abstract: To increase salmon production in the Alexander Creek drainage in Southcentral Alaska, invasive northern pike (Esox lucius) were suppressed annually in up to 69 side-sloughs of Alexander Creek from 2011 through 2018. During that time 20,035 invasive northern pike, ranging in length from 104 to 1,035 mm and with a greater male-to-female ratio, were captured and removed. Dietary preferences and prey distribution were analyzed with the stomach contents of 14,751 northern pike captured during suppression efforts. Of those, 17% of the northern pike stomachs were empty and 83% contained at least 1 prey item. The most common prey items in order of abundance were slimy sculpin (Cottus cognatus), juvenile salmon (Oncorhynchus spp.), threespine stickleback (Gasterosteus aculeatus), lamprey (Petromyzontidae), and leeches (Hirudinea). In addition, minnow-trapping events, coinciding with spring suppression efforts, were conducted annually from 2011 through 2016 to assess relative abundance and spatial and temporal distribution of juvenile salmon in Alexander Creek. For all 6 years, only 321 juvenile salmon were captured in minnow traps in spring, of which 38% were Chinook salmon (O. tshawytscha) and 62% were coho salmon (O. kisutch). Juvenile salmon catch rates in the Deshka River, a system with much less northern pike habitat, were much higher for both Chinook and coho salmon compared with Alexander Creek. After 4–6 years of northern pike suppression efforts, the 2014–2016 Alexander Creek aerial escapement indexes of spawning Chinook salmon increased to their highest levels in nearly a decade. However, low indexes in 2017 and 2018 reflect a pattern that other Susitna River systems (without northern pike) also experienced. Suppression efforts will probably need to continue for several more years before juvenile salmon productivity and adult salmon runs show strong signs of recovery.
Keywords: Northern pike, Esox lucius, Alexander Creek, suppression, invasive species, Chinook salmon, Oncorhynchus tshawytscha, Susitna River, Deshka River, gillnets, minnow traps, juvenile salmon, stomach contents.