To fisheries scientists, the specific cause tends to be not only unknown but unknowable. Since the signing of the first Great Lakes Water Quality Agreement in 1972, the International Joint Commission has received its biological advice only from fisheries biologists. Only in 1996 did the Commission appoint to the Science Advisory Board a biologist with wildlife training. There is a consensus within the fisheries agencies that it is not necessary to consider toxic contaminants, directly or indirectly, in understanding the status of Great Lakes fish populations. Thus the advice that the Commission has received over the first 24 years of the Agreement did not include damage to fish populations caused by pollutants, only advice on the use of fish based on health advisories.
Fisheries science is about to enter a period of intellectual crisis.
Through radio dating the layers of the core they have been able to reconstruct the history of contamination of Lake Ontario with specific pollutants. At the same time that the radio dating was being undertaken, toxicologists were finding that the eggs of lake trout are among the most sensitive of all vertebrates tested to this dioxin. Based on the amounts of dioxin in the layers of the sediment core and the amount that would be expected in the eggs corresponding to each layer, the scientists concluded that none of the lake trout eggs in Lake Ontario could have hatched since 1940. The Lake Ontario lake trout went extinct by the early 1950s and its prey, the deepwater sculpin, was extinct within about five years. This retrospective analysis is challenging the fisheries scientists consensus that there is no need to consider the action of toxic contaminants in understanding the dynamics of fish populations in the Great Lakes.