Inferring tributary-specific production of adult, wild steelhead to the Lake Michigan fishery using otolith chemistry

Grant: # 1726

Grant Amount: $152,737.39

Board Decision Year: 2017

Central Michigan University - Department of Biology and Institute for Great Lakes Research (Mt. Pleasant)

Department of Biology and Institute for Great Lakes Research

Pangle, Kevin ([email protected]) 989-774-3185

2017 Ecosystem Health and Sustainable Fish Populations: Ecological and Biological Research to Inform Management - Ecological and biological fisheries research to inform management

Project Details

Abstract: 

Mixed stock fisheries, which arise when multiple, spatially distinct natal sources contribute to a single adult population, pose unique challenges to fisheries managers due to their complex nature. The relative contributions of stocks and the degree of spatial mixing is still not well known for most fisheries, particularly those in large systems. Our study goal was to evaluate the stock composition of steelhead (Oncorhynchus mykiss) across the entirety of Lake Michigan populations, which are currently supported by extensive stocking from 6 hatcheries and substantial natural reproduction from numerous tributaries. From 2016 to 2018, 1,415 angler-harvested adult steelhead were collected. Natal origins were assigned to adult fish based on their otolith chemistry using a random forest classification model built with data from known-origin juvenile steelhead across the Lake Michigan basin. When validated with known-origin coded wire tagged adults, our model correctly classified 88% of fish. Among all years, 59% of adult fish were classified as hatchery origin and 41% as naturally produced based on otolith chemistry. The majority of hatchery origin fish were assigned to Wolf Lake State Fish Hatchery, accounting for 57%, 56%, and 77% of all hatchery fish in 2016, 2017, and 2018 respectively. In all years, the lake wide composition of hatchery origin adults was significantly different from what would be expected given stocking rates of each hatchery. The majority of wild origin fish (65%) were assigned to streams sites in the northern Lower Peninsula region of Michigan. Stock composition of wild fish was not significantly different across statistical districts in 2016, 2017 or 2018. Stock composition of hatchery fish was not significantly different across statistical districts in 2017 or 2018, but was in 2016. Our findings indicate that relatively few hatchery and wild stocks comprised the majority of angler harvested steelhead and these stocks were well mixed among years. Improved understanding of the stock structure and mixing patterns of steelhead in Lake Michigan will greatly improve managers’ abilities to sustainably and effectively manage for the future.

The final report for this project can be accessed at this link.