Progress Toward Lake Trout Rehabilitation at a Stocked and Unstocked Reef in Southern Lake Michigan

Abstract

Sustained efforts to restore naturally reproducing populations through the stocking of marked juvenile Lake Trout Salvelinus namaycush have occurred since the 1960s but have been largely unsuccessful in achieving that goal. Julian’s Reef in southwestern Lake Michigan has been a targeted Lake Trout rehabilitation site since 1985 and was designated a first-priority site in a revised management strategy for Lake Trout rehabilitation in 2011. We evaluated progress toward rehabilitation objectives for spawning Lake Trout at Julian’s Reef and compared that progress to unstocked Waukegan Reef nearby in light of a recent increase to approximately 50% unmarked adults at both sites, as detected by annual fall spawning assessments. We observed significant progress toward meeting the rehabilitation objectives for adult Lake Trout in southern Lake Michigan. The spawning populations at Julian’s Reef and Waukegan Reef did not differ in relative abundance, sex ratio, age structure, or spawner sources (stocking location; clipped or unclipped) except that the sex ratio at Waukegan Reef during the assessment period favored female spawners. These results suggest that the adult Lake Trout population is strong enough to permit natural recruitment in southern Lake Michigan, warranting the need to identify the source of natural reproduction so as to fully evaluate factors related to rehabilitation success. We propose that management agencies should consider investigating other unstocked sites where Lake Trout may be spawning and should revise their rehabilitation plans to include actions that could limit detrimental impacts on naturally reproducing populations where they exist.

Received October 15, 2015; accepted July 22, 2016 Published online November 10, 2016

ACKNOWLEDGMENTS

We thank Richard Hess, Dan Makauskas, Vic Santucci, and Tom Trudeau (IDNR staff); and Captain Arthur Atkinson, Ernie Booth, Tom Clark, Tom Wisnewski, and Ed Johnson (crew of the Clifford J) for their contributions to Lake Trout surveys at the study reefs. We also appreciate input from Vic Santucci and Dan Makauskas during the initial stages of manuscript preparation; Charles Madenjian (U.S. Geological Survey), John Dettmers (GLFC), Richard Hess (IDNR, retired), and the Lake Michigan Biological Station staff for providing helpful reviews that strengthened this manuscript; and the advice from four anonymous reviewers and Charles Madenjian during the final review. Sarah Huck’s assistance regarding the use of PRIMER is greatly appreciated. Financial support for this project was provided through Federal Aid in Sport Fish Restoration Project F-65-R (Illinois Lake Michigan Fishery Surveys and Investigations) and Project F-69-R (Research and Analysis of Fisheries in Illinois).