Lake Trout Reproduction Study at
Isle Royale National Park
BY MIKE SEIDER, ASHLAND FWCO
study at Isle Royale National Park. Credit: Dan Traynor, Michigan DNR
Late this spring, Ashland FWCO staff collaborated with researchers from the Michigan Department of Natural Resources, the University of Wisconsin – Milwaukee, NOAA Northwest Fisheries Science Center and National Park Service on a lake trout study at Isle Royale National Park.
The primary objective of the project was to characterize the seasonal reproductive activity of the various morphotypes of lake trout. At least, three morphotypes have been identified in Lake Superior: lean, siscowet, and humper. These forms have differing physical features such as head shape, fin length, and fat content, and often occupy different habitats.
Previous work has shown genetic differences between at least the lean and siscowet forms. To maintain these genetic differences, reproductive isolation must occur through differing reproductive timing and/or spawning locations. Previous research found the reproductive timing of the siscowet and lean lake trout along the south shore of Lake Superior were synchronous, however historical accounts suggest there may be more reproductive diversity, particularly around Isle Royale.
In 2013 and 2014, lake trout will be sampled each June, August and September at several locations around Isle Royale to track the reproductive progression of each morphotype. In addition to typical data collected from lake trout (e.g. length, weight, ageing structure, stomach contents), each fish is measured for fat content and photographed for later morphotype discrimination.
Genetic samples are collected to assess relatedness of the individuals collected over the three sampling events, to determine if they are from the same morphotype population. The fish’s gonads will be weighed and a portion collected for later determination of previous spawning activity and current reproductive status. The hope is that by sampling over the course of the season, the study will follow the reproductive progression and timing of spawning for each of the morphotypes found around Isle Royale. Furthermore, this study should help further quantify the frequency of a phenomenon known as “skipped spawning”, which has important implications to lake trout management.
There is interest in re-establishing various forms of lake trout in the lower Great Lakes and this project should provide more information about the reproductive timing and population dynamics of the morphotypes found in Lake Superior. Understanding the potential reproductive diversity among those stocks should aid managers in selecting potential stocking source populations for rehabilitation in the Great Lakes.