Midwest Fish & Wildlife Conference 2019

AUTHORS: Lydia R. Doerr, Dr. Patrick Forsythe, Dr. Christopher Houghton – University of Wisconsin-Green Bay; Scott Hansen, Wisconsin Department of Natural Resources; Dr. Kevin Pangel, Central Michigan University

ABSTRACT: Much remains unknown regarding the early life history of Lake Whitefish in the Great Lakes despite their ecological and economic importance. The capture of larval Lake Whitefish in four major Green Bay tributaries (Fox, Menominee, Peshtigo, and Oconto Rivers) indicates the re-establishment of potamodromous stocks and suggests that these tributaries contribute to the overall metapopulation. The collection of larvae from the Sturgeon Bay shipping canal and the other reefs throughout Green Bay provides evidence that Lake Whitefish are also spawning in nearshore habitats. The ability to identify natal origin of a specific population is essential to creating effective stock-specific management plans; capable of protecting various sub-population that make up the larger Lake Whitefish metapopulation. Larvae collected during 2017-2018 were used to examine whether otolith microchemistry can accurately determine natal origin of these individuals. Preliminary analyses found significant differences in the ratio of strontium and barium to calcium in riverine and offshore water chemistry for Green Bay and Lake Michigan.  The incorporation of these and other trace elements in larval otoliths allowed for the identification of natal origins of Lake Whitefish sub-populations. Otolith microchemistry proved successful at delineating natal origins at both broader level (i.e. tributary vs. open water) and at the site-specific scale.

AUTHORS: Andrew Ransom, Dr. Patrick Forsythe, Dr. Chris Houghton – University of Wisconsin-Green Bay

ABSTRACT: A resurgence of the Lake Whitefish (Coregonus clupeaformis) population within the waters of Green Bay has been documented in recent years despite overall low and stable numbers reported for Lake Michigan. Furthermore, large numbers of adult Lake Whitefish have been observed within major tributaries during the time of spawning in late fall. While our understanding of the ecology and behavior of Lake Whitefish in Lake Michigan is improving, knowledge gaps exist with these new river spawning ecotypes. Among these knowledge gaps are microhabitat selection in spawning locations, as well as timing and drivers of migration. In order to bridge these gaps, we used using Adaptive Resolution Imaging Sonar (ARIS) to monitor relative fish abundances in 10 sample locations with different physical characteristics (ie. flow rates and substrate type) on the Fox (n=5) and Menominee (n=5) Rivers in Wisconsin. To confirm egg deposition in spawning locations, suction sampling was also conducted throughout each river. Sampling was conducted in November and December of 2017 and 2018, in order to encompass the entire spawn period. Results will be used to influence potential restoration efforts for similar ecotypes across the Great Lakes.

AUTHORS: Joseph D. Schmitt, Christopher S. Vandergoot, Richard T. Kraus – USGS Great Lakes Science Center, Lake Erie Biological Station

ABSTRACT: Populations of coldwater fishes such as burbot Lota lota, lake whitefish Coregonus clupeaformis, and lake trout Salvelinus namaycush have declined in Lake Erie, while cisco Coregonus artedi have been extirpated. Warming temperature regimes and the re-eutrophication of Lake Erie have increased the frequency of harmful algal blooms and hypoxic events, which can reduce oxythermal habitat availability. Using vertical profile data collected in the central basin from 2008-2017, we developed generalized additive models to explore spatial, seasonal, and interannual trends in oxythermal habitat availability for lake trout, cisco, lake whitefish, and burbot based on published oxythermal niche benchmarks. Habitat availability was usually temperature-limited rather than oxygen-limited, and significant (P<0.05) monthly and interannual variations in habitat availability were detected for most species. In general, oxythermal habitat was most limited during August and September; moreover, significant interannual trends in habitat availability were also detected, with 2016 having the most extreme habitat reduction for many species due to record high temperatures. Understanding the spatiotemporal dynamics of oxythermal habitat availability will be important for the conservation and restoration of these fishes in our changing climate. Moreover, these models can be integrated with climate predictions to better understand how warming temperatures will affect coldwater habitat in the future.

AUTHORS: Brad Utrup, Jan-Michael Hessenauer, Andrew S. Briggs, Todd Wills, Michael Thomas (retired) – Michigan Department of Natural Resources

ABSTRACT: Age estimation is a fundamental part of fisheries management; critical for evaluations of growth, mortality and recruitment.  Validation of ages obtained from age estimation of hard structures is a necessary part of the ageing process in order to better understand the magnitude of error and bias associated with structure interpretation.  Validation studies on large-bodied and long-lived species such as Lake Sturgeon Acipenser fulvescens are challenging.  We utilized a 20-year mark-recapture dataset from Lake St. Clair and the St. Clair River, Michigan, USA to validate pectoral fin ray age estimates from 51 individuals that were sampled twice. The time at large ranged from 2 to 17 years between capture-recapture events.  All fin rays were aged by two separate readers (agreement rate 94.1%).  Samples were divided into four quartiles based on mean annual growth rates during their time at large.  Age error was defined as the difference between the age of the fish at first and second capture and the number of years at large.  No difference in time at large existed among the four groups, but age error differed among the four groups.  Furthermore, age error did not differ from zero for the two fastest growing quartiles but did differ significantly from zero for the two slowest growing quartiles.  We conclude that for Lake Sturgeon growing faster than 3 cm/year (generally less than 100 cm in TL) pectoral fin rays provide valid age estimates.  Managers should consider the growth rates of Lake Sturgeon in their populations for determining a size threshold for utilizing fin rays for age estimation.