Seasonal Movements of Chinook Salmon in Lake Michigan Based on Tag Recoveries from Recreational Fisheries and Catch Rates in Gill‐Net Assessments

Abstract

AbstractThere are no specific studies of the movements of introduced Chinook salmon Oncorhynchus tshawytscha in Lake Michigan, despite the need for such information for population assessments and stocking allocations. We investigated the seasonal distribution of hatchery‐reared Chinook salmon between May and September based on fishery‐dependent (recoveries from recreational fisheries of fish marked with coded wire tags [CWTs]) and fishery‐independent sources (catches in assessment gill‐net surveys). We modeled recoveries by fishing trips in Michigan waters of Lake Michigan to estimate spatially and temporally explicit abundance indices using generalized linear models (GLMs) and accounted for the efficiency among recovery sources (charter boat captain reports, creel clerk interviews, and headhunter collections of CWT samples from charter boat and non‐charter boat catches). Recovery levels varied among areas, months, years, and recovery sources, and distribution among areas also varied by month. We used CWT data with lakewide geographical coverage and evaluated the distributions of the absolute numbers of coded‐wire‐tagged fish recovered in Michigan and Wisconsin waters of Lake Michigan from all possible recovery sources. From both analyses we found that the distribution of Chinook salmon varied seasonally, with displacements from southern areas toward the north from May through summer, from inshore to offshore areas toward the west during summer, and movement back east in the fall. For the analysis of Chinook salmon catch rates in gill‐net assessments, we used GLMs to compare levels among months, statistical districts, years, nearshore and offshore areas, and different depths. The temporal and spatial trends were similar to those from the CWT analyses, and the distribution shifted toward deeper waters in July and August. Movement patterns coincided with favorable temperature and prey distribution and were consistent with those exhibited by the Pacific Ocean Chinook salmon population from which the Lake Michigan population originated. Seasonal changes in Chinook salmon distribution influence recreational fisheries, and stocking strategies should consider the influences of movement patterns on fishing opportunities in Lake Michigan.