Date of Award

2020

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Natural Resources

First Advisor

J. Ellen . Marsden

Abstract

Restoration and recovery of lake trout (Salvelinus namaycush) has been the focus of research and management in the Great Lakes and Lake Champlain since populations collapsed in the late 19th and 20th centuries. Wild juvenile lake trout recruitment was discovered in Lake Champlain in 2015 after 42 years of stocking efforts. Intensive biweekly bottom trawl sampling during the ice-free season was conducted from 2015 to 2018 to assess the extent of wild recruitment at three different sampling areas (north, central, south) of the Main Lake. The collection of wild and stocked lake trout in bottom trawls enabled analysis and comparison of growth and distribution between wild and stocked juveniles. Lake trout stocked at age-0 in Lake Champlain have established an adult population, therefore if growth of wild lake trout is similar to that of stocked fish of similar size, we assume they will have similar survival. To assess the potential for wild lake trout to survive past their first winter, a critical period in fish life history, I compared growth of juvenile lake trout in Lake Champlain spatially, seasonally, and by origin (wild or stocked). No consistent differences were found in growth rates between wild and stocked juveniles of similar size. In addition, and contrary to general assumptions, the data indicate that juvenile lake trout continue to grow in length while maintaining condition over the winter and therefore must be actively feeding. The percentage of wild juveniles was markedly higher in the central sampling area than the north and south, but no trend in growth was evident among sampling areas. The data from intensive bottom trawling also provided insight into the seasonal depth distribution of juvenile lake trout that can be used to design future juvenile assessments in Lake Champlain. I compared the distribution of wild and stocked lake trout by depth and temperature in the central sampling area of Lake Champlain based on seasonal changes in thermal stratification. Differences in distribution were most pronounced during thermal stratification, when wild lake trout were significantly more abundant in warm, shallow depths and stocked lake trout were more abundant in cold, deep areas. Overall, my results suggest that wild juvenile lake trout survival should be comparable to stocked juveniles in Lake Champlain, and differences in depth and temperature preferences can be used to develop a standardized survey to assess recruitment of wild lake trout.

Language

en

Number of Pages

105 p.

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