Structure and function of fish communities in the southern Lake Michigan basin with emphasis on restoration of native fish communities

The southern Lake Michigan basin in northwest Indiana possesses a variety o f aquatic habitats including riverine, palustrine, and lacustrine systems. The watershed draining this area is a remnant of glacial Lake Chicago and s upports fish communities that are typically low in species richness. Compos ition of the presettlement Lake Michigan fish community near the Indiana Du nes has been difficult to reconstruct. Existing data indicate that the numb er of native species in the Lake Michigan watershed, including nearshore La ke Michigan, has declined by 22% since the onset of European settlement. Fe w remnants of natural fish communities exist, and those occur principally i n the ponds of Miller Woods, the Grand Calumet Lagoons, and the Little Calu met River. These communities have maintained a relatively diverse assemblag e of fishes despite large-scale anthropogenic disturbances in the area, inc luding channelization, massive river redirection, fragmentation, habitat al teration, exotic species invasions, and the introduction of toxic chemicals . Data that we collected from 1985 to 1996 suggested that the Grand Calumet River has the highest proportion of exotic fish species of any inland wetl and in northwest Indiana. Along the Lake Michigan shoreline, another group of exotics (e.g., round goby, alewife, and sea lamprey) have affected the s tructure of native fish communities, thereby altering lake ecosystem functi on. Stocking programs contribute to the impairment of native communities. N onindigenous species have restructured the function of Lake Michigan tribut aries, causing disruptions in trophic dynamics, guild structure, and specie s diversity. Several fish communities have been reduced or eliminated by th e alteration and destruction of spawning and nursery areas. Degradation of habitats has caused an increase in numbers and populations of species able to tolerate and flourish when confronted with hydrologic alteration. Fish c ommunities found on public lands in northwest Indiana generally are of lowe r biological integrity, in terms of structure and function, than those on p rivate lands and are not acting as refugia for native fish populations. Sto cking of nonindigenous species should be evaluated to enable the restoratio n of native fish communities on public lands. Habitat quality will need to be improved and land-use modifications decreased or reversed in order to re store or slow the decline in native fish communities.