Apparent extirpation of prey fish communities following the introduction of Northern Pike (Esox lucius)

Abstract

We examined the long-term effects on prey fish communities of introducing Northern Pike (Esox lucius), a top predator fish, into small, Boreal shield lakes lacking natural piscivore populations. During 1987-1994, Northern Pike were introduced into lakes 110, 221, and 227 in the Experimental lakes Area in northwestern Ontario, Canada. In lake 227, prey fish were undetectable three years after the addition of Northern Pike. Although Northern Pike were removed from the lake by 1996, multiple independent visual and trapping surveys have yielded no evidence of any fish in lake 227 since then. In 1994-1995, 85% of the Northern Pike were removed from lake 221. In 2012, despite intensive sampling efforts using baited minnow traps, fyke nets, trap netting, gill netting, angling, and visual observation, no forage fish of any species was observed or caught in lake 110 or 221. In all three lakes where Northern Pike were added, prey fish populations were extirpated or too small to detect. In lake 221, we estimated the current population of Northern Pike to be 49 ± 37, a 59% decrease since 2000 when prey fish were still present. the mean total length and body condition of Northern Pike in lake 221 had not changed since the prey community collapsed. our findings suggest that the introduction of Northern Pike into lakes without natural piscivore populations has long-lasting effects on fish community structure, to the detriment of both Northern Pike and prey fish populations.