The Great Lakes Science Center has conducted lake-wide bottom trawl surveys
of the fish community in Lake Michigan each fall since 1973. These systema
tic surveys are performed at depths of 9 to 110 m at each of seven index si
tes around Lake Michigan. Zebra mussel (Dreissena polymorpha) popu lations
have expanded to all survey locations and at a level to sufficiently contri
bute to the bottom trawl catches. The quagga (Dreissena bugensis), recently
reported in Lake Michigan, was likely in the catches though not recognized
. Dreissena spp. biomass ranged from about 0.6 to 15 kg/ha at the various s
ites in 1999. Dreissenid mussels were found at depths of 9 to 82 m, with th
eir peak biomass at 27 to 46 m. The colonization of these exotic mussels ha
s ecological implications as well as potential ramifications on the ability
to sample fish consistently and effectively with bottom trawls in Lake Mic
higan.