When I was working for MSU on the mortality study at the Ludington Pumped Storage Facility we were running our open lake gillnets at sampling stations north and south of the plant. We caught a washed-out brook trout that was solely identifiable by the contrasting striping on its ventral fins, but really pale and 3YO by scale aging which should be accurate for salmonines that young. After checking the fish over for fin clips and finding none, we concluded that he was a fish that had flushed-out of a river. my point is that coasters do exist in the lower Great Lakes. That sadi, the majority of them are found in Lake Superpior. One thing I should have added was an MDNR genetic analysis of inshore caught "coaster" brook trout on the north shore of the U.P. conducted by the MDNR Essentially they found that these fish were a genetic amalgam of several populations of stream brook trout from the Salmon Trout River westward over to Keweenaw Bay, indicating that this open lake stock consisted of excess production from a variety of flash basin streams with low productivity, several of them forming anchor ice in severe winter, further diminishing their prodcutivity and conseqent carrying capacity.
Carl the easy answer to your second question is to simply point-out that Lake Superior, of all the Great Lakes, has the fewest invasive species including a near abence of Dreissenid mussels other than a colony near the mouth of the St Louis River over by Duluth, MN/Superior, Wi. that has thus far failed to expand, yet still survives, courtesy of the outflow plume of the St, Louis. In reality, other than their impacts on decline and disappearance of the deepwater amphipod, Diporeia sp., invasive mussels have diverted production rather tha 'removed" it from the water column. By displacing Diporeia sp. quagga mussels have short circuited the physical cycling of demersally trapped nutrients, outside of isothermic intervals when the entire water column is subject to wind driven mechanical mixing. Consequently, the nutrients "lost" to the system are actually sequestered within about a meter of the substrate in the invasive mussel colonies that now blanket the substrate, even soft-bottom substrate due to shell build-up forming a hard-pan cementum layer that mussels colonize. With this Baltic invader came round goby, and an invasive amphipod, Echinogammarus ischnus, that colonize the mussel beds. The mussels poop-out a packet of pseuo-feces that are fragmented by chironomid larvae and invasive amphipod grazing activity with all nutrients released quickly taken-up by filamentous algae that colonize the mussel colonies, basically a nearly intact little commensalistic colony of invasives. Steve Pothoven, NOAA Great Lakes lab. researcher worked-up some extimates to conclude that invasive inshore mussel colonies can filter the entire water column, top to bottom, at depths out to 90 meters during periods where wind and wave actiivity generated mixing of the water column was minimal, over an interval of a little over a week! Round goby are conseqently VERY abundant, far more than alewife used to be back in the 1970's. However, they have a caloric density roughly half that of an equivalent length alewife or smelt, obligating any fish species that opts to consume them to eat them at twice the rate to retain their conversion efficiency and growth rate. Now, toss-in the predation rates on round goby, per estimates made by the folks at MSU's Quantitative Fishery Center are so high in both Lakes Huron and Michigan that Round Goby seldom survive to Age-III where they are big enough to feed on quagga sp mussels, serving as a partial check to their expansion. Consequently biomass of invasiv mussels continues to increase as density declines inshore out to100M. Lake Huron is roughly half the Total Carbonate Hardness value of Lake Michigan, reducing both the production of round goby and their caloric density relative to Lake Michigan. The secondary conduit for biotic transfer of demersal energy back to surface waters in Lakes Michigan and Huron is Mysis diluviana, which has seen about a 79% decline in numbers as well. There used to b summer long functional stocks of large cladoceran zooplankton like Daphmia sp and Bosmina sp., even when alewife were dominant. Now, the zooplanktong stock shifts quickly over to the omnivorous copepod, Limnocalanus sp., particuarly in the northern portions of the basin and outside of the Bays de Noc. Basically this reflects that improved water clarity due to declines in biogenic turbidity values. Much like Alaska, several States encourage sport fishers to dump their fish carcasses back into the system offshore to stimulate productivity.