Robert J. Sheffer | Geology Reports

USGS2025

Muskellunge spawning habitat characteristics and availability in Green Bay, Lake Michigan

Objective Habitat degradation has been associated with the loss of many self-sustaining Muskellunge Esox masquinongy populations, including those in Green Bay, where stocking has provided an exceptional trophy fishery but restoration goals include establishing self-sustaining populations and there is little evidence of natural recruitment. Our objectives were to determine whether (1) Muskellunge spawning locations and occurrence of successful hatching were related to a suite of habitat characteristics, (2) proportions of Muskellunge spawning in or outside of tributaries to lower Green Bay were different, and (3) Muskellunge showed spawning site fidelity. Methods From 2017 to 2019, adult Muskellunge ( N = 60) were surgically implanted with radio and acoustic transmitters to identify spawning locations, where we measured a suite of habitat variables and attempted to collect eggs and larvae. Side-scan sonar was used to quantify the amount of habitat available to Muskellunge for egg deposition in the Fox and Menominee rivers, which are tributaries to Green Bay. Results Muskellunge eggs were collected at 58 locations, but only two larvae were collected from a single location. Bottom slope, depth, distance to shore, gravel substrate, organic matter, and dissolved oxygen best predicted the presence of Muskellunge eggs. We determined that little habitat associated with Muskellunge egg deposition was available in the Fox and Menominee rivers. However, approximately half of tagged Muskellunge appeared to spawn outside of tributaries. Muskellunge in Green Bay displayed moderate spawning site fidelity. Conclusions Our results suggest that successful hatching occurs at very low levels and the lack of suitable Muskellunge spawning habitat in Green Bay tributaries may be limiting natural reproduction. Changes in spatial allocation of stocked fish and enhancement of known spawning locations may increase egg deposition and subsequent natural reproduction.

Michigan, Wisconsin↗

USGS2022

Mark-recapture models accurately predict growth trajectories of known-age Muskellunge in Green Bay, Lake Michigan

Length-at-age data are commonly used to describe growth of fish, and obtaining these data typically involves estimating ages from calcified structures (e.g., fin spines or rays, otoliths, or cleithra). Verifying the accuracy of age and growth estimates for long-lived fish is often difficult because known-age fish are not available for all ages in a population. Mark–recapture methods offer nonlethal alternatives for estimating growth of fish that do not require age data. However, few studies have compared growth trajectories estimated from mark–recapture data with trajectories estimated using the standard von Bertalanffy growth function (VBGF) incorporating length-at-age data from known-age fish. We used a robust data set of Muskellunge Esox masquinongy sampled from Green Bay, Lake Michigan, during 1990–2018 to compare growth trajectories estimated from three mark–recapture models and a VBGF fitted to length-at-age data from known-age individuals. Growth trajectories estimated with mark–recapture models were similar to trajectories estimated with a VBGF using known-age fish. Our results suggest that using recapture of tagged fish provides a viable alternative for describing Muskellunge growth trajectories compared with using ages estimated from calcified structures, where incorrect age estimates represent an additional source of error.

Wisconsin↗