Measuring Fish Assemblages in Great Lakes Coastal Wetlands, Les Cheneaux, Michigan: A Program Assessment

Abstract

Les Cheneaux Islands constitute an archipelago along the shoreline of Michigan’s eastern upper peninsula, containing coastal wetlands that provide key supports for fishes in the Laurentian Great Lakes. This thesis reports unpublished 1996 survey data used to evaluate fish assemblages in Les Cheneaux coastal wetlands. It is also a program assessment of fish survey methods in Les Cheneaux marshes from 1996-2004, growing from the 1996 survey recommendations. In 1996, I sampled larval and adult fish assemblages from ice-off to ice-on in four bays: Cedarville, Mackinac, Mismer, and St. Martin. From 1997-2004, larval and adult fishes were sampled in Cedarville, Mackinac, Mismer, McKay, and Prentiss bays. The 1996 survey focused on open water and what proved to be seasonal marsh areas. Visual surveys identified more diverse zonations, from permanent marsh through seasonal marsh to open water. Subsequent years focused on the seasonal and permanent marsh. I found that electroshocking and seining were ineffective for sampling these marsh habitats. Gill nets were highly effective but only accurate when nets with variable mesh sizes were used. Fyke nets and minnow traps proved most useful, accurately sampling fishes in densely vegetated marsh. The key for effectively sampling all areas of the marsh is to deploy multiple methods with good overlap across zones, testing and validating methods. Fish assemblages were typical of lacustrine habitats and varied among methods, habitats, bays and with time. Results of the 1996 survey showed July and August were key sampling times because richness and abundance were highest. Subsequent surveys demonstrated that extended sampling protocols are preferable to short surveys when evaluating habitat utilization of marsh fishes. Overall, this thesis and subsequent research in Les Cheneaux Islands support

studies showing that conservation of Great Lakes shoreline habitats will be important for the success of fish populations that depend on them.