NEAFWA 2018

AUTHORS: J. Ellen Marsden, Madeline N. Schumacher - University of Vermont

ABSTRACT. Lake trout disappeared from Lake Champlain by 1900; since 1973, annual stocking of age-0 and yearlings has established a feral population. The first evidence of natural recruitment was not seen until 2015, when focused bottom trawling for juvenile lake trout captured 303 age-0 to age-3 fish, of which 72 (23%) were wild (i.e., progeny of stocked fish). The proportion increased to 33% in 2016, and 50% in 2017, with increasing proportions of young-of-the-year lake trout each year. Our goal is to understand what factors are involved in this sudden successful recruitment of wild lake trout. We analyzed diet and condition of 622 wild lake trout and 870 stocked lake trout between 50 and 400 mm total length collected in May to November 2015-2017. Stocked fish were, on average, the size of wild fish one year older. Average Fulton’s condition factor was slightly higher overall for stocked fish (0.90) than wild fish (0.83), and higher in spring and fall than mid-summer. Mysis comprised 90-100% of the diet (by number) of age-0 and spring yearling wild lake trout, and 45-54% of the summer and fall diet of age-1 fish. In contrast, only 15-60% of the diet of age-0 stocked fish, seasonally, was Mysis. By age 1, the diet of stocked fish was very similar to that of the wild age-2 lake trout, consisting of small smelt, sculpin, alewife, and Mysis. The low diet overlap of age-0 wild and stocked fish suggests competition is not likely to be a limiting factor for survival; instead, recruitment may depend on availability and abundance of Mysis. Mysis populations declined dramatically in the 1990s and have not apparently recovered. Changes in distribution, local abundance, or spatial overlap of Mysis with age-0 lake trout may potentially explain recent recruitment of young lake trout.