10 
in size and in some physical characteristics. From Lake Ontario, which is di- 
rectly connected to the Gulf of St. Lawrence, it is thought to have passed into 
Lake Erie through the waters of the Welland Canal. The new canal was opened 
first on April 20, 1931, and officially on August 6, 1931. A single specimen was 
reported by Dymond (1932) for Lake Erie on September 23 of the same year. 
Two years later the species was recovered in Lake Huron, but apparently it is 
not at all abundant in any of the lakes above Niagara. Its effect on other species 
is inadequately known. It is a forage species for lake trout, but whether it in- 
troduces any detrimental food or spatial competition is an open question. 
The smelt was introduced in another way. After a couple of unsuccessful 
plantings, specimens from a landlocked population in New England were trans- 
ferred to Crystal Lake in Benzie County, Michigan, in 1913. The purpose of 
this introduction was to provide more food for the indigenous lake trout. From 
Crystal Lake the smelt escaped into Lake Michigan, and on into Lake Huron. 
Whether or not smelts are important in the diet of lake trout has not been shown. 
They destroy lake shiners and in this way compete with the trout for food. They 
themselves, however, have added to the total commercial catch of the Great 
Lakes. From 1931 to 1939 the yearly catch of smelts averaged a little over a 
million pounds per year. From this amount, there were other increases until 
in the years 1940-1943 the catch averaged over 3.6 million pounds annually. In 
1944 this fishery spectacularly collapsed, and only 4,500 pounds were taken. 
The smelt population built up again until in 1947 the take had increased to 
786,000 pounds. The cause of this fluctuation is not specifically known, but Van 
Oosten (1949) believes that the spectacular decrease was caused by some un- 
known bacterial or virus disease. 
Now we come to an entirely different denizen, the sea lamprey, which is 
not really a fish, It is a low vertebrate, and except for a free-living larval pe- 
riod it is entirely parasitic on fish. For a mouth, it is furnished with a sucking 
disc which is lined with sharp teeth. The lamprey fastens itself to a fish and 
rasps an opening into the body, from, which it extracts blood and fragments of 
flesh. Lampreys have been recorded by several workers as attaching them- 
selves to bottoms of boats, and they have been seen fastened to the hulls of lake 
boats passing from Lake Huron into Lake Superior. It is thought probable by 
many biologists that the introduction into the upper Great Lakes occurred in 
this manner through the Welland Canal. 
Now we face this problem: Is the introduction and multiplication of the 
sea lamprey the cause of the remarkable reduction in fish production of the 
Great Lakes? As Langlois (1951) says, ‘‘These facts could explain the sudden 
drastic decline in the catch of lake trout.’’ It may be significant that the least 
affected lake, Superior, still has the best trout fishery. Furthermore, there is 
good synchrony between the rise in lamprey numbers and the fall in trout num- 
bers. But, as we have already said, the connection between cause and effect is 
often thoroughly snarled. 
Popular interest in the sea lamprey has been largely in relation to the 
production of lake trout. The destruction of the trout fishery has been astound- 
