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... In 1991 and 1992, more than 50,000 fish representing 24 species were sampled in the Pend Oreille River of which only 174 (<0.4 %) were WCT (Bennett and DuPont 1993). Prior to 1952 (Completion of Albeni Falls Dam), the Pend Oreille River was considered a good cutthroat trout fishery (Horner 1989 in Bennett and. ...
... Coil pers. comm. in Bennett and DuPont 1993). Now, the river has primarily silt and sand substrates, and water temperatures reaching 24.5 o C during summer months (Bennett and DuPont 1993). ...
... comm. in Bennett and DuPont 1993). Now, the river has primarily silt and sand substrates, and water temperatures reaching 24.5 o C during summer months (Bennett and DuPont 1993). The Pend Oreille River was found to lack quality habitat for salmonids and is likely better suited for spiny-rayed predators. ...
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Ivlev's electivity index and the forage ratio, two commonly used measures of food selection, are significantly biased when the sizes of the prey samples from the gut of the predator and the habitat are unequal. Approximate confidence-interval expressions are derived for these indices. A stochastic (Monte Carlo) model was used to validate these expressions and to explore the statistical properties of the indices. The statistical reliability of each index is shown to be a function of the absolute and relative sample sizes and the relative abundances of the prey species in the environment. A linear index of food selection is proposed which avoids most of the statistical and mathematical inadequacies of these indices. Regardless of the index used, however, inadequate habitat sampling, differential availability of prey to the predator, and differential digestion of prey may be significant sources of error in the interpretation of food selection data.
Fish food habits were arrayed in a vector diagram such that food habits are related to trophic level. Fish communities in the lakes are discussed with reference to water chemistry and susceptibility to potential lake acidification. -from Sport Fishery Abstracts
Early growth and mortality rates for the 1977 year class of largemouth bass Micropterus salmoides were estimated and compared to the initial year class of largemouth bass after impoundment of West Point Reservoir in 1975. The population fecundity was estimated before spawning to be 422,000 mature ova per hectare in littoral areas. The number of young of the year ranged from 1,138 per hectare in May to 20 per hectare in August. Monthly instantaneous mortality rates for the 1977 year class were 0.872 between June and September 1977 and 0.213 between May 1977 and August 1978. Survival was estimated as: 0.22% from spawning to brood dispersal; 5.88% from brood dispersal in early June to early September 1977; and 0.002% if the estimate for population fecundity is used as the number of eggs spawned surviving to August 1978. The monthly instantaneous growth rate was 1.645 between May and September 1977. The observed biomass of young-of-the-year largemouth bass in September was 5.83 kg per hectare. Greater numbers and larger-sized fish were present in 1975. Mortality was greater for the initial 1975 year class, and included early fishing mortality.
This study's objective was to quantify the water depth, water velocity, and substrate used by adult brown trout Salmo trutta for feeding and spawning in rivers. General hypotheses were: (1) brown trout prefer specific magnitudes of environmental variables and occupy positions through choice; (2) the preferred value of any variable for a particular activity is the same in all rivers; (3) brown trout prefer different values of the same variable for different activities. Surface observation was used to locate 140 feeding and 140 spawning positions used by brown trout in both isolated and sympatric (with rainbow trout Salmo gairdneri) populations in six diverse rivers in New Zealand. Brown trout (mean fork length 42 cm) preferred a mean depth of 65.0 cm and a mean velocity of 26.7 cm second at the position occupied by the fish for feeding, but for spawning they preferred a mean depth of 31.7 cm, a mean velocity of 39.4 cm second, and a mean substrate size of 14.0 mm. Analysis of variance showed brown trout preferred the same velocity for the same activity in all rivers and years regardless of whether they were from allopatric or sympatric populations, but microhabitats used for feeding and spawning were significantly different. Velocity appeared to be the most important factor determining position choice but ranking of factors may vary with the type of activity. Brown trout chose positions with optimum combinations of depth and velocity instead of positions with more preferred values of either factor alone. Population size may be limited by the amount of the least abundant activity-specific microhabitat.Received May 22, 1982 Accepted March 8, 1983