We examined stomach contents of 906 age-0 and older walleyes Stizostedion vitreum vitreum and 1,575 age-2 and older yellow perch Perca flavescens, collected from western Lake Erie in 1979-1981, to measure preferences for prey type and size and diet overlap among different size groups of these two percids. Seasonal diets closely followed changes in forage-fish availability. Walleyes ate age-1 shiners Notropis atherinoides and N. hudsonius in spring, but switched to age-0 clupeids Dorosoma cepedianum and AIosa pseudoharengus in summer and autumn. Diet selection was governed by abundance of appropriate-size prey and preferences for forage species. Yellow perch ate invertebrates in spring but clupeids and shiners thereafter; electivity values for prey were low compared with those of walleyes, indicating that yellow perch were the more opportunistic feeders. Diet overlap was greatest among walleye age groups (0, 1, and 2-and-older) and least between walleyes and yellow perch. We hypothesize that density-dependent processes within the percid community probably will occur during years of low shiner and clupeid abundance and that they will be most intense for walleyes. Walleyes were less size-selective and grew more slowly in 1979-1981 than in 1959-1960, suggesting that forage-fish availability has declined in the presence of increased walleye stocks. Yellow perch should be less affected by forage-fish reductions if invertebrates are plentiful. Abundant stocks of walleyes Stizostedion vitreum vitreum and yellow perch Perca flavescens support valuable sport and commercial fisheriesin western Lake Erie. Commercial harvest of walleyes, which was as great as 6,985 t in 1956, reached an historic low of 213 t in 1969, pre-• Present address: Lake Erie Fishery Unit, Ohio
As part of the Episodic Response Project (ERP), we studied the effects of episodic acidification on fish in 13 small streams in the northeastern United States: four streams in the Adirondack region of New York, four streams in the Catskills, New York, and five streams in the northern Appalachian Plateau, Pennsylvania. In situ bioassays with brook trout (Salvelinus fontinalis) and a forage fish species (blacknose dace (Rhinichthys atratulus), mottled sculpin (Cottus bairdi), or slimy sculpin (Cottus cognatus), depending on the region) measured direct toxicity. Movements of individual brook trout, in relation to stream chemistry, were monitored using radiotelemetry. Electrofishing surveys assessed fish community status and the density and biomass of brook trout in each stream. During low flow, all streams except one had chemical conditions considered suitable for the survival and reproduction of most fish species (median pH 6.0‐7.2 during low flow; inorganic Al < 60 μg/L). ERP streams with suitable conditions during low flow, but moderate‐to‐severe episodic acidification during high flow, had higher fish mortality in bioassays, net down‐stream movement of brook trout during events, and lower brook trout density and biomass compared to nonacidic streams, and lacked acid‐sensitive fish species (blacknose dace and sculpin). Movement of trout into refugia (areas with higher pH and lower Al) during episodes partially mitigated the adverse effects of episodes. Recolonization from alkaline tributaries or microhabitats can maintain low densities of fish in streams that experience severe acidic episodes, but it is not sufficient to sustain fish densities and community composition at levels expected in the absence of these episodes. Fish responses to acid‐base chemistry were fairly consistent across regions. In general, trout abundance was reduced and acid‐sensitive fish species were absent from ERP streams with median pH < 5.0‐5.2 during high flow and inorganic Al > 100‐200 μg/L. We conclude that episodic acidification can have long‐term effects on fish communities in small streams.
Bevelhimer, M. S., 8. A. Stein, and 8. F. Carline. 1985. Assessing significance of physiological differences among three esocids with a bioenergetics model. Can. ). Fish. Aquat. Sci. 42: 57-69.To predict stocking success of esocids in Ohio waters with different thermal regimes, we measured individual food consumption, conversion efficiency, growth, and metabolic rate for Ohio stocks of northern pike (Esox lucius), muskellunge (E. rnasquinongy), and their hybrid, tiger muskellunge, in laboratory experiments. The first three parameters were quantified during 2-wk experiments of ad libitum feeding on fathead minnows (Pimeohales prome8as) at seven constant temperatures (5, 15, 20, 22.5, 25, 27.5, and 30°C). The food consumption and growth data suggest that northern pike shouid grow faster than muskellunge at cool temperatures (~2 0°C )~ but slower than muskeSlunge at warm temperatures (>25"C). Latitudinal differences in their natural distributions might explain this observation. Growth data of the hybrid showed no such obvious relationship to either of the parents. Metabolic rates were determined by measuring oxygen consumption in a closed, static respirorneter at five constant temperatures (5,15,20, 25, and 30°C). We found little difference in metabolic rates among the three taxa. To examine these data further, we used a bioenergetics model that simulated different stocking conditions, both natural (thermal regime and prey availabiiity) and human controlled (stocking size and date). With this model, we predicted growth for 12-15 rno after stocking. In general, summer-stocked fish were about 35-90% larger 15 mo after stocking than were fall-stocked fish 12 mo after stocking. More specifically, the combined effect of ration and temperature permitted hybrids to grow faster than the parents in all simulations. Northern pike grew larger than muskellunge in a cool system, but smaller than muskellunge in a warm system with summer stocking. Based on bioenergetic considerations, tiger muskeIlunge should outgrow both northern pike and muskellunge in thermal regimes common to Bhio waters.Pour determiner B e succes de B'ensemencement d'esocides dans des cours d'eau de differentes temperatures en Ohio, nous avons mesure la consommation d'elements nutritifs et leur transformation, le taux de croissance et le metabolisme du brochet ( b o x lercius), du rnaskinonge (E. rnasgerinongy) et de I'hybride resultant du croisement de ces deuxespeces, en etudiant en Baboratoire des sujets prelevks dans Ies stocks de IfOhio. Nous avons quantifi6 les trois premiers parametres mentionnes ci-dessus en etudiant pendant 2 sem des tetes-de-boules (P8'mephales promelas) noknrries 3 volontk et consew6es sept temperatures differentes (5, 15,20, 22,5, 25, 27,s et 30°C). Bfapres les resultats que nous avons obtenus sur la consommatisn de nourriture et la croissance, le brochet devrait se developper plus rapidernent que le maskinong6 en eau froide (~2 0°C ) et plus lentement en eau chaude (B25"C). Ce phkwomene s'explique peut-&re par la difference de ...
The triolein-filled semipermeable membrane device (SPMD) is a simple and effective method of assessing the presence of waterborne hydrophobic chemicals. Uptake rate constants for individual chemicals are needed to accurately relate the amounts of chemicals accumulated by the SPMD to dissolved water concentrations. Brown trout and SPMDs were exposed to PCB-contaminated groundwater in a spring for 28 days to calculate and compare uptake rates of specific PCB congeners by the two matrixes. Total PCB congener concentrations in water samples from the spring were assessed and corrected for estimated total organic carbon (TOC) sorption to estimate total dissolved concentrations. Whole and dissolved concentrations averaged 4.9 and 3.7 µg/L, respectively, during the exposure. Total concentrations of PCBs in fish rose from 0.06 to 118.3 µg/g during the 28-day exposure, while concentrations in the SPMD rose from 0.03 to 203.4 µg/ g. Uptake rate constants (k 1 ) estimated for SPMDs and brown trout were very similar, with k 1 values for SPMDs ranging from one to two times those of the fish. The pattern of congener uptake by the fish and SPMDs was also similar. The rates of uptake generally increased or decreased with increasing K OW , depending on the assumption of presence or absence of TOC.
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