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Diet of Lake Trout in Otsego Lake, NY: Insights from stomach contents, biochemical markers, and isotopic tracers
Farese, Nicholas
Farese, Nicholas
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2025-05
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Farese_Thesis.pdf
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The diet of Lake Trout from Otsego Lake, NY has varied amidst a history of non-native species introductions. Despite their short residency in Otsego Lake (c.1986-2012), Alewife became the main component of Lake Trout diet after their introduction. However, the current diet of Lake Trout remains largely unknown since Alewife were extirpated. The objective of this study was to determine the current diet of Lake Trout using stomach content analysis (SCA), fatty acid analysis (FAA), and stable isotope analysis (SIA). Adult Lake Trout were collected during the falls of 2021 and 2022, while potential prey species were captured seasonally from 2021 to 2023. Fatty acids were quantified using gas chromatography mass spectroscopy, which were used to evaluate diet using quantitative fatty acid signature analysis (QFASA). Stable isotopes 13C and 15N were quantified using an elemental analyzer interfaced to an isotope ratio mass spectrometer, which were used to estimate diet through Bayesian two source mixing models. SCA indicates that Lake Trout diet was composed primarily of Chironomids (57.1%, frequency of occurrence), Dreissenids (28.6%), Slimy Sculpin (22.9%), and Lake Trout eggs (20.0%). A subset of the species collected were used to evaluate diet using FAA and SIA, which included Bluegill, Chironomids, Dreissenids, Rainbow Smelt, Rock Bass, Slimy Sculpin, Smallmouth Bass, White Sucker, and Yellow Perch. The fatty acid signatures and stable isotope ratios of these prey were found to be significantly different, satisfying an assumption of both analyses. FAA identified Slimy Sculpin, Bluegill, Dreissenids, and Rainbow Smelt as likely prey, whereas SIA revealed that Rainbow Smelt, Slimy Sculpin, and Dreissenids were the dominant prey. Together, these findings indicate a dietary shift back to Slimy Sculpin as the primary prey for Lake Trout in the absence of Alewife, providing crucial insights for managing this keystone sportfish in Otsego Lake.