Matt Kornis analyzed both salmonine food habits, stratified by location, season, percent diet composition, as well as percent ration composition. He then assessed dietary overlap by Salmonine species based on stable isotope analyzed food habits for salmonines.
These data broadly overlap with the brown trout plant and catch analysis trend data that Jay Wesley has posted in this thread.
The bottom-line trend that is evident is that fish forage (alewife, yellow perch, round goby, bloater DWS, Slimy sculpin0 confers proportionally more calories than invertebrate forage, seasonally and annually to Lake Michigan salmonines, with alewife remaining the most important component from a specie array analysis, with a general increase in round goby incidence and proportion contribution through time. Chinook salmon, brown trout, coho salmon, steelhead were highly dependent on alewife intake, while lake trout exhibited the broadest array of fish forage arrayed by species. Brown trout had high dietary overlap with all salmon, as well as steelhead trout, with slightly lower dietary overlap with lake trout.
When you compare caloric density of individual forage fish matched by size, alewife have roughly twice the caloric content for a length matched specimen when compared to round goby. As alewife distribution has declined numerically within the basin, numeric offset via round goby density increases have trended upward. Due to caloric density value differences, energy ration for those salmonines that have increased utilization of round goby as forage items has not offset energy intake declines from a shift away from alewife dominated foraging.
There is also some additional data on seasonal inshore movement of lake trout for the Lake Michigan basin that indicates that a higher proportion of the lake trout stock within the Lake Michigan basin moves into inshore waters in the spring on the east side when compared to inshore movement patterns exhibited by lake trout on the west side of the basin.
Slowed growth via diminished alewife ration intake, seasonally as well as annually through time, as well as diminished survival of brown trout in inshore waters of the eastern portion of the Lake Michigan basin has been the broad result.
The folks at the MDNR Charlevoix Research station have developed a small semi-submersible that can track a specific transect, enabling it to visually record round goby densities of substrates that cannot be sampled with traditional otter trawls or acoustic sampling techniques.