Impact of logging and natural fires on fish communities of Laurentian Shield lakes

The goal of this study was to determine if natural fires and logging have a significant impact on abundance, growth, and size structure of fish populations in 38 lakes of the Laurentian Shield (Québec, Canada). The watersheds of nine of these lakes underwent logging and nine underwent natural fires, while the 20 remaining lakes were used as references. No significant differences were found among the three lake groups in the catch per unit of effort of the most abundant species: white sucker (Catostomus commersoni), northern pike (Esox lucius), yellow perch (Perca flavescens), lake whitefish (Coregonus clupeaformis), fallfish (Semotilus corporalis), brook trout (Salvelinus fontinalis), walleye (Stizostedion vitreum), and burbot (Lota lota). No significant difference was found among control, burned, and logged lakes in the back-calculated length of yellow perch, for which age determinations were made. However, we found that the proportions of small yellow perch and white sucker were significantly lower in populations of impacted lakes (burned and logged lakes pooled). The influence of logging and fires remained significant when a series of biotic and abiotic variables on watershed and lake characteristics were accounted for in multiple regression analyses. The lower proportion of small fish in impacted lakes could be due to an increase in postemergence mortality or to a shift of individuals to the pelagic zone.

Seasonal occurrence, recruitment, and maturation of Allocreadium lobatum Wallin, 1909 (Digenea: Allocreadiidae) in the fallfish, Semotilus corporalis Mitchell, in a New Brunswick, Canada, lake system

The seasonal occurrence, recruitment, and maturation dynamics of Allocreadium lobatum (Digenea: Allocreadiidae) infecting the fallfish, Semotilus corporalis, from the Magaguadavic Lakes system, New Brunswick, Canada, were studied from May 1978 through July 1978 and from February 1979 through November 1980. Allocreadium lobatum has an annual cycle with both low mean intensity and low prevalence of infection occurring from July through September and increasing to high levels from November through May. Parasite recruitment, marked by the presence of a high percentage (≥ 58%) of immature and mature worms in fallfish, is greater from August through November but occurs intermittantly throughout the year. From February through July at least 60% of the parasite population is composed of gravid individuals which die after oviposition. The seasonality of parasite occurrence, recruitment, and maturation cycles is discussed in relation to temperature changes of the water, host diet, and trends in the occurrence of amphipods which are the second intermediate hosts of A. lobatum.

Age and growth of the fallfish Semotilus corporalis with daily otolith increments as a method of annulus verification

Daily increments were found in the otoliths of the fallfish Semotilus corporalis from three stream populations in central New York. By counting these increments one can verify annual marks and validate other less precise methods of aging. Results suggested that a false first annulus was observed in the only previous study of fallfish age and growth. Annual growth in length is shown to be linear. All three populations' growth rates were significantly different. Furthermore, the difference among these local populations can account for much of the.variability in the rate of growth exhibited throughout the species' range. It is therefore proposed that the nature of the local habitat, in particular the size of the stream and the density of conspecifics, may be the major determinant of the rate of growth in the fallfish.

Metorchis conjunctus (Cobbold, 1860) Looss, 1899 (Trematoda: Opisthorchiidae): isolation of metacercariae from fish hosts

After 40 years Lac Edouard, Québec (46°45′ N, 72°55′ W), remains a focus of Metorchis conjunctus. Prevalence of infection differs for species of fish: Catostomus commersoni (100.0%), C. catostomus (81.8%), Semotilus corporalis (78.3%), and Salvelinus fontinalis (71.4%). All cysts isolated from S. fontinalis had a dense calcium coat.Many metacercariae, recovered after digestion of the fish in acid–pepsin solution, were viable and infective to domestic cats. Viability apparently depended on time of collection since more encysted larvae were found to be viable in October (32.4%) than in May (19.6%). Metacercariae of M. conjunctus were distributed in C. commersoni in an anterior–posterior density gradient. Anterior regions of the fish were more likely to be penetrated by the cercariae, based on both density and percent of metacercariae recovered. It is concluded, as a result of this study, that fish swim into clouds of cercariae which actively penetrate into the musculature of the fish.