Geology topics

David E. Ostergaard

Publications and source records attributed to David E. Ostergaard.

3 recordsLinked to original sources

USGS1993

Survival of lake trout stocked in U.S. Waters of Lake Ontario

Lake trout Salvelinus namaycush of the 1979–1990 year-classes (Lake Superior strain) were marked and stocked as fingerlings or yearlings in U.S. waters of Lake Ontario and recaptured during annual surveys with trawls and gill nets. Catches (as proportions of fish stocked) of age-2 fish by trawls and age-3 fish by gill nets were used as indices of survival. Mean survival indices of stocked fish declined over 50% from the 1980 to the 1990 year-class for fish stocked as yearlings and declined more than 90% for those stocked as fingerlings. Survival indices for fish stocked as yearlings were negatively and significantly correlated with abundance indices of large (≥550 mm total length) lake trout caught in gill nets in the year of stocking. This relation was not significant for fish stocked as fingerlings. Mean weight at stocking more than doubled for yearlings and increased by about one-third for fingerlings during this study. The increase in size at stocking may have offset what would otherwise have been a more drastic increase in mortality due to predation.

North American Journal of Fisheries Management↗

USGS1989

Effect of rearing density on poststocking survival of lake trout in Lake Ontario

Six paired lots of yearling lake trout ( Salvelinus namaycush ) reared at densities of 41,000 and 51,000 fish per raceway during their last 9 months in the hatchery were stocked in Lake Ontario. Poststocking survival of the high-density (HD) and low-density (LD) fish was not different for the 1982 year-class. However, for the 1983 year-class, mean survival was significantly different between HD and LD fish ( P < 0.01). Mean survival of HD fish was only 76% that of LD fish ( P < 0.01), and most of the mortality attributable to rearing conditions had apparently occurred within 2 months after stocking. Mean size at stocking was not different for HD and LD fish of the 1982 year-class, but for the 1983 year-class, the LD fish were 6% longer and 22% heavier than the HD fish. Mean lengths and weights of LD and HD fish were not different in samples collected in Lake Ontario at age 2 and older. Size at stocking was not likely the factor that caused the difference in survival. Rather, the rearing conditions (probably water exchange rate in relation to number of fish in the raceway) that resulted in slower growth of the HD fish of the 1983 year-class also caused them to be poorer physiologically than the LD fish. The number of yearling lake trout per rearing unit that will result in maximum contribution to populations in the Great Lakes after stocking may be lower than the rearing densities customarily used at some hatcheries.

Progressive Fish-Culturist↗

USGS1988

Comparison of hatchery-reared lake trout stocked as fall fingerlings and as spring yearlings in Lake Ontario

We made 16 paired releases of lake trout Salvelinus namaycush of four year classes (1979–1982) at five locations to compare survival and growth of hatchery-reared fish stocked as fall fingerlings (FF) and as spring yearlings (SY). Comparisons were based on fish at ages 2–8 recovered with bottom trawls, with gill nets, and from anglers' catches. Mean lengths and weights were greater for SY than for FF at all ages, and SY attained sexual maturity at an earlier age than FF. The survival of FF may have been affected by average size at stocking and by the severity of the weather during the first winter after stocking. Survival ratios of SY to FF lake trout from stocking to age 2 ranged from 1.32:1 to 6.80:1, and a ratio of 2.41:1 was considered to be typical. Stocking cost per 1,000 fish was US$21.76 for FF and $35.45 for SY. Under the most cost-effective hatchery regime for producing lake trout (the maximum number of SY plus some FF to fully utilize hatchery space and personnel year round), rearing cost per 1,000 fish was estimated to be $235.41 for SY and $38.75 for FF.

North American Journal of Fisheries Management↗