Fish in Troubled Waters

With inauguration of the deepened Welland Canal and the St. Lawrence Seaway, Great Lakes shipping and the commerce related to it received a stimulus which the promoters of the Seaway had promised. But not all commercial activity was to prosper in the same fashion. As in most instances when large engineering works alter the physical environment in a significant way, there were some unanticipated adverse consequences. The aquatic ecology of the Great Lakes system was to experience a series of wrenches having dramatic results.

Opening of the Great Lakes to ocean-going vessels permitted invasion by unprecedented numbers of sea lamprey, an eel-like marine parasite which attaches itself to larger hosts, injecting a substance that dilutes the host's blood from which it draws its nourishment. The lake trout became its most celebrated prey and within a period a few years the commercial catch fell from 5.5 million pounds to about 400 pounds. The lake trout commercial fishery was for all practical purposes finished.

With the demise of the lake trout, the alewife, a small boney shake anadromous fish upon which the lake trout fed, began multiplying at a phenomenal rate in the altered aquatic environment. The alewife tended to feed on smaller forage fishes which were a link in the food chain of the Great Lakes smelt, perch, and similar fish, threatening these as well as the trout commercial fishery. But perhaps the most spectacular result of the alewife population explosion was the periodic die-off of the fish; lacking a predator population, large masses would live out their lives to be washed upon the shore, creating a health as well as an aesthetic nuisance.

In time, the cooperative efforts of Canadian and U.S. fisheries biologists came to control the lamprey infestation by use of electric wires to block access to the lamprey spawning grounds, and through selective poisoning of lamprey young that managed to survive despite the measures to prevent the reproduction cycle. The long-term viability of the sea lamprey population seemed to be checked in this manner, but eradication of the parasite promised to be a long way off—perhaps somewhere into the distant 1970s. Accordingly, with a slow-maturing fish lake trout, susceptible to continuing depredation by the residual lamprey population, there was need for a fishery of another species if the Great Lakes were to be rehabilitated with a sport and commercial fishery.

The original attempts to reintroduce trout into the Great Lakes were not successful. The splake, Canadian developed hybrid of the lake trout, did not respond successfully in Lake Michigan where it was tried, nor did other freshwater species with which experiments were taken. Saltwater species such as the striped bass, which had shown capacity to develop viable populations under landlocked conditions were considered, but fisheries biologists ultimately opted for the silver salmon or coho. The coho, a short-lived, fast-growing species, would tend to repopulate more quickly. Another advantage was that much artificial rearing work had been done with coho in hatcheries in the Pacific Northwest. If successful, the coho would offer predator control of the alewives and at the same time provide an early and exciting sport fishery. Thus, in 1964 with a million fertilized coho eggs obtained from the state of Oregon, the Michigan fisheries biologists launched a great experiment.

By March of 1966 about 650,000 salmon smolt were released into three streams draining into Lake Michigan, another 200,000 were released into the Big Huron River of the Upper Peninsula, destined for Lake Superior. Results exceeded fondest expectations. The 5-inch smolt of the spring release had attained lengths of 24 inches and weights of up to 7 pounds by the autumn run of the early maturing, second-year jack salmon. By the third year, the normal spawning cycle for the typical coho, 12-pound fish were being caught and excitement gripped the sports fishing community. Of the 650,000 smolt released, 350,000 were recovered either by sports fishermen or by the fisheries personnel for stripping or commercial sale when hatchery capacities were filled. Five million eggs were recovered for the hatcheries to further the artificial rearing and rehabilitation program. Expectations were for releasing 10 million or more coho smolt annually within a few years of experience with the developing program.

Hopes were high in 1968 as these plans were being formulated. The 650,000 released smolt represented a gross understocking of the vast potential of the lake—roughly an ounce of fish per 24 acres. Yet even this stocking made salmon sport fishing a recreational asset. Literally thousands of boats were engaged fishing on a given weekend in the prespawning concentrations offshore. An estimated 15,000 fishermen were out for salmon on a single day, and fishing continued along the streams as the fish moved up to spawn. With roughly 10 or 15 times the initial year's number of smolt planned for release annually, the sports fishing and commercial implications of this miracle of fisheries management were truly phenomenal. Euphoric predictions of a 5 million adult coho harvest by sports fishermen annually by the end of a ten-year development and rehabilitation period characterized the situation as the year 1968 drew to a close.

Events in 1969 were no less dramatic, but quite different. In March the U.S. Food and Drug Administration in a routine check of the commercial salmon pack discovered residues of DDT in the fish far exceeding the maximum allowed in beef fat to pass FDA standards. Lower forms of aquatic life that sift near-microscopic plankton out of large volumes of water passing through their "winnowing mechanism" have long been known to be amazingly efficient concentrators of pesticides. Higher up in the food chain, predators ingest significant amounts of pesticides in this way. But in the case of Lake Michigan coho, it has been discovered that fish can also absorb pesticides from water which passes through their gills. In this way, as well as by feeding on smaller fishes which similarly concentrate DDT, the salmon have accumulated DDT in amounts equal to 12 parts per million overall, and as much as 90 parts per million in some of the fatty tissues.

The consequences of this development cannot be known with certainty. There are serious implications for reproduction of the salmon, for DDT tends to concentrate in the fatty tissues, which means it will be found in high concentrations in the yolk of the egg on which the unhatched embryo feeds. This seems to be the explanation for a die-off of young in the hatchery in 1968. But the implications may be wider than salmon and sport fishing. Persistent pesticides in some non aquatic species appear to alter production of enzymes that break down female sex hormones and affect reproduction in other ways. DDT is thus likely to be the most serious environmental hazard to higher life forms as well as to Lake Michigan salmon. Government action taken in November to ban the use of DDT by the end of 1970 in all but carefully specified situations may have come in time to reverse the buildup trend. It may not have been in time for the coho salmon.