The stock of lake herring (Coregonus artedii) in the Apostle Islands (Wisconsin) region of western Lake Superior has diminished severely during the past 30 yr, and predation by rainbow smelt (Osmerus mordax) on herring larvae has been considered a possible cause of this decline. In contrast, the herring stock in Black Bay, 160 km to the northeast, has remained nearly stable despite the presence of large numbers of smelt and high commercial production of herring. Predator–prey interactions were studied in both areas during 1974. Herring larvae and smelt were about 120 and 3 times as dense, respectively, in Black Bay as in the Apostle Islands region. Substantial predation by smelt on young herring was evident in Black Bay, where 17% of 1195 smelt stomachs examined contained herring larvae. From calculations of the relative densities of the two species, and of the daily ration of the predators, we estimated that smelt consumed 3.3–11% of the herring larvae. Nevertheless, the herring stocks have sustained average historical levels of commercial production. In contrast, no herring larvae were found in the stomachs of 1711 smelt collected in the Apostle Islands region. We conclude that predation by smelt on herring larvae is not the major factor controlling or suppressing herring stocks in either region. Key words: lake herring, rainbow smelt, predation, Lake Superior

The Gull Island Reef lake trout (Salvelinus namaycush) population was one of the few in Lake Superior that was not annihilated by the combined effects of excessive fishing and sea lamprey (Petromyzon marinus) predation. Following control of the lamprey in the early 1960s, this population of lake trout began a slow but steady increase in the average age and numbers of lake trout. Total annual mortality rates for spawning lake trout were 32% for age VI fish, 48% for ages VII–VIII, and 75% for ages IX and older. These total mortality rates included a 7.3% exploitation rate u, a 20% natural mortality n, and annual lamprey-induced mortalities of 6% for ages V–VI, 24%, for ages VII–VIII, and 56% for ages IX and older fish. The estimated number of lake trout eggs deposited annually on Gull Island Reef from 1964 to 1979 ranged from 3.3 million eggs in 1965 to 28 million eggs in 1979, with a mean of 9 million eggs per year. At present levels of lamprey predation, the estimated egg to spawning fish return rate on Gull Island Reef is 0.18%.Key words: lake trout, sea lamprey, survival, population structure, egg deposition

The early life history of freshwater drum, Aplodinotus grunniens, was studied in 1965–67 to determine factors influencing year‐class strength in a main stem Missouri River reservoir. Fish spawning occurred over a period of 6–7 weeks in June and July when water temperatures reached 18 C. Fecundity of fish 307 to 386 mm long and 6–9 years old ranged from 34,000 to 66,500 ova. Ova reared in the laboratory at a water temperature of 23 C hatched in 27 hr and the prolarvae averaged 3.2 mm long. The prolarval stage was complete 45 hr after hatching and postlarvae averaged 4.4 mm long. Adult characters developed at an approximate length of 15 mm. Diet of fish 6–15 mm long was Daphnia and Cyclops. Bottom fauna became important in the diet of fish longer than 20 mm. Fish movement between channel and floodplain was related to changes in diet. Growth, year‐class strength, and mortality varied among years. Strong year classes were associated with warm summer (June‐August) water temperatures in the spawning and nursery area and weak year classes with cold temperatures. Size of year class was determined before fish attained a length of 25 mm.

Yellow perch Perca flavescens were sampled annually in 1973-1988 with bottom trawls in Chequamegon Bay, Lake Superior. Biomass averaged 1.6 kg/hectare. Fish 1-3 years old made up 64% of the biomass, whereas fish of harvestable size (>4 years old) made up only 31% of the biomass. Year-class strength was variable among years, but a Ricker recruitment function described the relation between year-class strength and parental stock size. Age-specific mortality increased substantially as fish became sexually mature at age 4, perhaps as a result of energy depletion associated with high reproductive and maintenance costs in a suboptimal thermal environment. Yield-per-recruit analysis indicated that most of the age-specific annual mortality was due to natural causes. Natural mortality, rather than limited recruitment or fishing mortality, was the major factor controlling harvestable stock size. Regardless of the size of a year-class produced, natural mortality greatly reduced its abundance prior to maturity and recruitment to the fishable stock. This high mortality, combined with very slow growth, limits the biomass potential of the harvestable stock, and sustainable yields from this population are therefore low.