Green Bay FWCO Fish Biologist Assists in Completion
of Isle Royale Lake Trout Research Project
BY MATTHEW KORNIS, GREEN BAY FWCO
hoists a siscowet lake trout captured for research on morphological diversity. Credit:
Andy Jasonowicz, NOAA
Dr. Matthew Kornis, a fish biologist and data analyst from the Green Bay Fish and Wildlife Conservation Office (FWCO), spent the weeks of August 11th and September 22nd assisting a team of Great Lakes scientists studying lake trout morphotypes in Lake Superior near Isle Royale National Park. The cooperative study, which was coauthored by Charles Bronte from the Green Bay FWCO and funded by a competitive grant from the Great Lakes Fishery Commission, included researchers from the Michigan Department of Natural Resources (DNR), the National Oceanographic Atmospheric Administration (NOAA) Northwest Fisheries Science Center, the Ashland FWCO, the National Park Service, and the University of Wisconsin-Milwaukee.
Over the past two years, this research team sampled lake trout during spring, summer and fall using gill nets deployed from the Michigan DNR’s R/V Lake Char. Lake trout are among the world’s most morphologically diverse fish species, meaning that physical characteristics of lake trout (e.g., body shape, head shape, pigmentation) are highly variable and can reflect different genetic backgrounds and/or environmental conditions. In Lake Superior, there are four principal morphotypes of lake trout: leans (low fat content, found in relatively shallow water), siscowets (high fat content, found in very deep water), humpers (slow-growing fish associated with underwater reefs) and redfins (fish with elongated fins often found at moderate depth).
siscowet lake trout for a digital photograph. The red light down the
center of the fish helps line up the head, body, tail and fins for
morphometric measurements. Credit: Matt Kornis, USFWS
One objective of this study was to further document differences in morphometric measurements and compare genetic relatedness, muscle lipid levels, gonadosomatic index (GSI) and length-at-age among the four morphotypes. The various lake trout morphotypes also reproduce at different times of year in Lake Superior and especially near Isle Royale. Thus, another objective of the study was to characterize spatial and temporal isolation in the reproduction of each morphotype by examining eggs from mature females to evaluate fecundity, and by collecting and fixing cross-sections of gonads so that histological examination could determine the developmental stage of male and female gametes. By characterizing morphological diversity and reproductive life histories in Lake Superior lake trout, this study will provide additional insight into alternative options for restoring lake trout in the lower Great Lakes, which lost this diversity due to lake trout population crashes caused by sea lamprey predation and overfishing.
Dr. Kornis also helped the scientists with a pilot study that placed archival satellite tags on several large lake trout of different morphotypes during the week of August 11th. The tags, which are engineered to release from the fish at a predetermined date, were recovered the week of September 22nd. Over this six week time period, each tag collected continuous data on the depth, location and temperature experienced by the tagged trout. Although the field component of the original two year study is complete, pilot studies such as this could motivate additional lake trout research projects in the future.