Fluctuations in the Success of Year-Classes of Whitefish Populations with Special Reference to Lake Erie
Authors: Lawler G. H. 
Published: April 2011

Year-class strength varied markedly in whitefish (Coregonus clupeaformis Mitchill) populations, and the presence of unusually strong year-classes was evident in the commercial catch. Fluctuations in the catch characterized the Lake Erie fishery and the unusually high production in some years was attributed to the occurrence of strong year-classes in the fishery. The most outstanding year-class in Lake Erie originated in the spring of 1944 and resulted in the highest catches ever recorded in the year 1948 and 1949. The next strongest year-class occurred in 1936 and resulted in high production in 1940 and 1941. The 1926 year-class was relatively strong and was responsible for subsequent high production. Other peaks in production could not be attributed to the presence of strong year-classes, as no age composition data were available, but it was inferred that strong year-classes were responsible. The 1943 year-class was unusually successful in Lake Huron, Green Bay (Michigan), and the upper portion of Lake Michigan. There is some evidence that year-classes of above average strength may have occurred in Lake Huron in the past, but were not as prevalent or as striking as those that occurred in Lake Erie. The 1944 year-class was dominant in the Lesser Slave Lake whitefish catch. There is no evidence that unusually successful year-classes have ever appeared in Lake Ontario, Lake Winnipeg, Great Slave Lake, or Heming Lake.The whitefish is at the southernmost limit of its distribution in Lake Erie and here environmental conditions, especially temperature, have become progressively unfavorable. The increase in the abundance of species accustomed to more southern warmer conditions was further evidence that the lake itself is becoming warmer at a rather rapid rate.In Lake Erie the above average strength of the 1926, 1936, 1944, and other year-classes which were considered strong cannot be explained on the basis of the size of spawning population, the number of hatchery-raised fry planted, nor on the effect of such conditions as wind, turbidity, precipitation, and water level.Embryonic development of the whitefish was restricted to a very narrow range of temperature, the optimum for development being close to 33 F (0.5 C). The occurrence and continued survival of this species is limited to waters which maintain a temperature close to the freezing point during development and hatching.It was concluded that spawning at temperatures above 43 F (6.1 C) is probably unsuccessful.In Lake Erie there was considerable variation in developmental temperatures from year to year, and only rarely did temperature conditions approach the optimum for embryonic development. Strong year-classes in Lake Erie resulted only when the following suitable set of temperature conditions prevailed: (1) fall temperatures should drop early to 43 F (6.1 C), the temperature below which most successful spawning occurs; (2) the temperature decrease to the optimum for development should be steady and not fluctuating; (3) the spring temperature should increase slowly and late, thus providing a prolonged incubation period at near optimum developmental temperatures. In years that strong year-classes arose, spring temperatures began to rise 2 weeks to 1 month later than in years that whitefish year-classes were not unusually strong. Weak year-classes occurred when one or more of these conditions were adverse.As the whitefish is a cold-water species, it is to be expected that maximum reproduction (assuming other conditions favorable) will occur only when the water temperature approaches that of more northern lakes. If Lake Erie continues to warm, the environment will become even less conducive to coregonines and the residual population will be confined to the deep basin at the eastern end or become extinct.The question of why lower-than-average temperature conditions did not result in the establishment of dominant year-classes in neighboring Lakes Huron and Ontario in the same year that they occurred in Lake Erie was discussed; the conclusion is reached that while temperatures were probably favorable for producing good populations, other conditions for survival may have been unfavorable and the occurrence of successful year-classes was dependent on other factors peculiar to the individual lake.Some aspects of dominance, including the simultaneous occurrence of strong year-classes in several species of Lake Erie fish were discussed. It was suggested that, although the important concept of "critical" periods in the success of year-classes was of great significance, consideration be given to the possibility of conditions that may be more broadly favorable — in time and space.