Changes in Mysis and Pontoporeia populations in southeastern Lake Michigan: A response to shifts in the fish community

We compared Mysis abundance and body length in 1977, a year of low benthivore abundance, to 1984–1985, years of high benthivore abundance. We also compared Pontoporeia abundance and body length between low benthivore years (1979, 1980) and high benthivore years (1984, 1985). Mysis densities between 20 and 50 m did not differ significantly among years, but their densities offshore (80–100 m) declined from 313 m−2 in 1977 to 59 m−2 in 1985. Mysis mean size did not differ significantly during this time, but there were changes in the length-frequency distribution. Mean Pontoporeia densities declined more than twofold between 1980 and 1984–1985. Pontoporeia mean size was unchanged during this time, but there were changes in the length-frequency distribution. The shifts in these macrobenthic species coincided with shifts in the fish community, suggesting a link to changes in predation rates on the benthos.