The production of lake trout, Cristivomer namaycush (Walbaum), in the United States waters of Lake Huron was highest in the earliest years for which there are statistical records, averaging 2,362,000 pounds in 1879–1894. The general level of yield was much lower but relatively stable in 1895–1939, during which period the catch averaged 1,685,000 pounds. The most recent years have seen a rapid and calamitous decline in the output; setting a new record low each year, the take decreased from 940,000 pounds in 1940 to only 38,000 pounds in 1946.

The production of lake trout in the Canadian waters of Lake Huron was generally low from 1867 up to about 1883, apparently because the fishery was then in the process of development. After 1882 the yield was relatively high for 26 years and then fell away progressively as the following averages of production in pounds for different periods show: (1883–1908) Huron proper–1,749,000, Georgian Bay (including the North Channel)–2,475,000, Canadian total–4,224,000; (1909–1922) Canadian total (no data for regions within the lake)–3,753,000; (1923–1939) Huron proper–1,600,000, Georgian Bay–1,996,000, Canadian total–3,596,000. During more recent years the catch fell from 1,038,000 pounds in 1940 to 29,000 pounds in 1946 in Huron proper, from 1,688,000 to 702,000 pounds in Georgian Bay, and from 2,726,000 to 731,000 pounds in all Canadian waters.

The tremendous decreases in production that have occurred in all parts of Lake Huron in recent years are generally believed to have been caused by a reduction in the abundance of lake trout resulting from attacks by the sea lamprey, which has become established and has multiplied rapidly in the upper Great Lakes.

Data are available on the production of lake trout in six local regions or statistical districts of the United States waters of Lake Huron (boundaries shown in Fig. 1) in 1891–1908 and on production, fishing intensity, and the abundance of fish on the grounds in 1929–1946. The order of the districts with respect to their percentage contribution to the average annual production was the same in 1891–1908 and 1929–1943. Certain changes occurred, nevertheless, in all percentages. The northern districts (H-1, H-2) which contributed 70.3 percent of the take in 1891–1908 accounted for only 56.2 percent in 1929–1943 whereas the central (H-3, H-4) and southern (H-5, H-6) districts which yielded 18.7 and 11.0 percent, respectively, in the former period contributed 25.5 and 18.3 percent in the latter.

The six districts were similar in 1929–1946 in that in all of them (1) most of the years of highest output and of most intensive fishing occurred in the early to middle 1930′s and (2) the earlier high levels were followed by declines that ultimately reduced production and fishing intensity to insignificance. The same (earlier high values followed by a decline) held for the abundance of lake trout in the northerly five districts, but the trends of fluctuation in the abundance in H-6 were opposite those in other areas.

On the whole, the abundance of lake trout appeared to have little effect on fishing intensity for the species. Only in H-1 did the two exhibit significant positive correlation whereas in H-6 they showed highly significant negative correlation. Most of the factors that may counteract the expected influence of abundance on fishing intensity (economic conditions, weather, …) cannot be evaluated accurately. It was determined, however, that the collapse of the whitefish fishery in the middle and late 1930′s most probably exerted a significant depressing effect on the intensity of the gill-net fishery for lake trout in those districts (H-1, H-4, H-6) in which the two species are ordinarily captured together.

The estimated abundance of lake trout in the United States waters of Lake Huron (all districts combined) had reached an extremely low level in 1946 (24 percent of the 1929–1943 average), and the complete collapse of the fishery in late years is a matter of record. The rate of decline in abundance, however, was much less rapid than the spectacular decreases in production might suggest. Although each year beginning with 1940 saw a new record low yield, the abundance was still 87 percent of average in 1942 and did not drop below 70 percent until 1944. This seeming paradox is explained by the fact that relative to average conditions, fishing intensity in 1941–1946 was lower and was decreasing much more rapidly than was abundance.