摘要:

In Lake Atnsjo, Southeastern Norway, Arctic charSalvelinus alpinusand brown troutSalmo truttaboth attained sexual maturity mainly at 6 years of age and older, usually at a body length larger than 26 cm. Both species have been heavily exploited at least since the turn of the century. The annual survival rate was estimated at 0.38 for Arctic char (age-groups 6–9) and 0.49 for brown trout (age-groups 4–9). Mean female age at maturity was higher than the optimal age at maturity predicted if female reproductive success only depended on fecundity. We argue that reproductive advantages of larger parental body size, due to high competitive ability during spawning, favored late female maturation and also limited the selective effect by the fishery for earlier maturation.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0141:AASASM>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Homing and straying patterns of fall chinook salmonOncorhynchus tshawytschaoriginating from five Columbia River hatcheries were assessed from coded-wire-tag data for the 1977, 1978, and 1979 brood years. There was considerable variation in both the tendency of different populations to stray and where they strayed. Homing ranged from 90.1% (of 372 fish) for the Lewis River to 72.5% (of 342 fish) for the Cowlitz River. Very few chinook salmon strayed into the Washougal River and Abernathy Creek, but the Lewis and Kalama rivers attracted many strays. The numerous strays from the Cowlitz River in 1980 probably were influenced by volcanic ash from Mount Saint Helens, Washington. Apart from the Cowlitz River fish, homing varied interannually from 8 to 19.3%. More older chinook salmon strayed than did the youngest age-group. The overall levels of straying were higher than have generally been reported for salmon and, if continued, could cause substantial genetic interchange among populations.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0150:HASPOF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We assessed the compatibility of alewivesAlosa pseudoharengusand gizzard shadDorosoma cepedianumthrough comparison of their distributional, reproductive, and early life history characteristics in Smith Mountain Lake, Virginia, a hydroelectric impoundment where these clupeids have coexisted for 20 years. Larval gizzard shad (<30 mm total length, TL) were most likely to be affected by alewives through trophic competition and predation. However, gizzard shad larvae were concentrated in uplake, littoral areas when alewives of all ages were downlake and pelagic. Gizzard shad spawning was virtually completed in June but most alewife spawning occurred in July. Gizzard shad larvae grew faster (1.33 mm/d) than alewife larvae (0.84 mm/d) throughout the summer. Alewife larvae 5–30 mm TL exhibited lower mortality (mean, 11.0%/d) than gizzard shad larvae (means: 40.1%/d and 12.9%/d for length-groups of 7.0–12.0 and 12.5–30.0 mm TL, respectively). Earlier spawning and faster growth of gizzard shad provided a high degree of temporal isolation, limiting both interference and exploitative competition with alewife larvae. We concluded that alewives and gizzard shad are compatible in Smith Mountain Lake and will likely be so in other systems of similar morphometry and water quality. However, potential negative impacts on other fish dictate that the alewife should be considered with extreme caution as a forage-species candidate.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0157:COAAGS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Shifts in microhabitat selection by rainbow troutOncorhynchus mykisswere related to seasonal and ontogenetic factors in a small stream characterized by short riffles, small pools, and boulder substrate. Resource availability did not differ significantly between summer and November sampling dates for most variables related to water velocity, substrate, and cover, although depths were greater and temperatures were significantly lower in November. Ontogenetic shifts were found for total depth, focal elevation, mean water column velocity, focal velocity, surface velocity, and substrate, but not for relative depth or temperature. When microhabitat selection was adjusted for fish size, selection was significantly different between seasons, most notably for velocity. Ontogenetic shifts in microhabitat use by young-of-year rainbow trout were interrupted by cooling winter temperatures. These changes resulted in substantially different microhabitat requirements for all rainbow trout size-classes in different seasons.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0166:SCIMSB>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

High-gradient boulder-bed streams have been the sites of relatively few studies of salmonid spawning habitat, although they have geomorphic and hydraulic characteristics—and therefore gravel distributions—that are quite different from the more commonly described lowergradient channels. We documented gravel distribution in seven high-gradient stream reaches in the eastern Sierra Nevada. Gravels occurred only in locations characterized by relatively low shear stress; they formed small pockets in sites of flow divergence and larger deposits upstream of natural hydraulic controls. In 1986 (a wet year), all tracer gravels placed in gravel pockets at nine sites on four streams were completely swept away, and substantial scour, fill, and other channel changes occurred at many sites. In 1987 (a dry year), tracer gravels and the channel cross sections were generally stable. Periodic mobility of gravel may explain why brown troutSalmo truttaare more abundant than rainbow troutOncorhynchus mykissin the study reaches, where high flows occur every May and June during snowmelt. Brown trout are fall spawners, and their fry emerge long before the high snowmelt flows, whereas rainbow trout are spring spawners whose eggs are in the gravel, and thus vulnerable to scour, during snowmelt flows.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0177:DASOPS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Year-class strength of striped bassMorone saxatilisis often determined by the success of first-feeding larvae. In the Sacramento–San Joaquin estuary, this success may be influenced by the recent invasion of exotic copepods that appear to be displacing native copepods important as food. We tested selection by larval striped bass on native copepods (Eurytemora affinisandCyclopssp.) and on introduced copepods (Sinocalanus doerriandPseudodiaptomus forbesi). Two-species and single-species tests established the following order of preference:Cyclopssp. (most preferred),E. affinis,P. forbesi, andS. doerri(rarely eaten). Tests to evaluate the underlying mechanism of prey selection showed that the presence of egg sacs and copepod size did not affect the larvae's choice of prey. Instead, selection by larval striped bass apparently involved differences in copepod swimming and escape behaviors.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0187:SPBLSB>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We sampled phytoplankton, zooplankton, and alewivesAlosa pseudoharengusand measured water temperature in Lake Ontario during 1981–1986. Through the use of general linear regression models we then sought evidence of control of the eplimnetic zooplankton community (mid-July to mid-October) by producers, consumers, and temperature. Our measures of the zooplankton community were total biomass, cladoceran biomass, and the ratio of large to smallDaphniaspp. (D. galeata mendotaeandD. retrocurva). Zooplankton population variables assessed were abundance, egg ratio, and productivity. Through factor analysis, factors were created from the standardized, transformed independent variables for use in the regression analyses. Regression models showed significant inverse relationships (P< 0.05) between alewives andBosmina longirostris(abundance, production, and egg ratio),Ceriodaphnia lacustris(egg ratio), andDaphnia retrocurva(egg ratio).Bosmina longirostrisandD. retrocurvaegg ratios were inversely related to algae biomass (<20 μm), thus the smaller algae might be controlled in part by the zooplankton community. Production ofC. lacustriswas directly related to temperature, as was the production and abundance ofTropocyclops prasinus. The annual size-frequency distributions ofB. longirostrisandD. retrocurvawere inversely related to yearling alewife abundance and directly related to adult alewife abundance, which suggested that yearlings use a particulate-feeding mode on these zooplankton species more frequently than adults. We found no significant negative correlations among the zooplankton species, which suggested that interzooplankton predation and competition were not as important in structuring the community as were planktivory and temperature.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0193:ROPFAT>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We measured survival of caged overwintering young-of-the-year and introduced, free-swimming adult smallmouth bass Micropterus dolomieui in five Ontario lakes that varied in pH from 4.9 to 5.9 (winter values). No hatchery-reared young survived in lakes that ranged in pH from 4.9 to 5.9 and in total aluminum from 55 to 215 μg/L. The only lake in which young survived the winter (2–100% survival) had a pH of 5.9 and a total Al of 34 μg/L. Survival of overwintering young in the laboratory was high (92–100%) at all pH levels tested (4.9–6.0). Differences in metal (AI, Cu, Zn, Ni, Mn) concentrations may account for survival differences between the field and laboratory and between lakes with similar pH. Adult smallmouth bass were transferred to four of the same lakes (19–24 fish/lake) used for the experiment on young fish. Population size estimates for the introduced adults were obtained from snorkeling surveys conducted during three spawning seasons (1987–1989). Estimated population size, expressed as a percentage of the number stocked, was highest (41–55%) in the lake with pH 5.9, low (4–12%) in the lake with pH 5.4, and zero in two lakes with pH 4.9–5.2.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0209:SOISBI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Growth and food conversion efficiency of hybrid bass juveniles (female striped bassMorone saxatilis× male white bassM. chrysops) were measured as a function of diel oscillating and constant temperatures, spring (increasing day length) and autumnal (decreasing day length) photoperiods, and ration sizes ranging from no food to daily satiation. The optimum temperatures for growth and peak conversion efficiency were estimated to be 26.8 and 21.2°C, respectively, for fish under constant temperatures, 12 h of daylight, and a maximum ration size. Springtime photoperiod significantly increased growth, and autumnal photoperiod significantly reduced growth. There was a significant temperature-photoperiod interaction; maximum growth occurred at 27.9°C under the springtime photoperiod and at 25.7°C under the autumnal photoperiod. Diel temperature oscillations with an amplitude of ±4, 6, and 8°C did not influence growth rate or conversion efficiency. Reduced ration sizes led to a lower optimum temperature for growth. Manipulation of temperature and photoperiod may be advantageous where feasible in intensive culture of hybrid bass. In field situations, stocking hybrid bass, a temperate eurytherm, may be successful where stocking striped bass, a temperate mesotherm, has failed because of thermal restrictions.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0217:EOTPAR>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We quantified diet and compared field estimates of growth and daily ration with predictions from a bioenergetic model for young-of-year muskellungeEsox masquinongy, northern pikeE. lucius, and tiger muskellungeE. masquinongy×E. luciusintroduced into five Ohio reservoirs. Gizzard shadDorosoma cepedianumdominated esocid diets (77–97% by weight) through autumn but were absent by spring. Diets in late autumn and spring included sunfishesLepomisspp. and brook silversidesLabidesthes sicculus. Northern pike and tiger muskellunge grew faster than muskellunge through the first year. Food consumption was highest for tiger muskellunge, followed by northern pike, then muskellunge. Growth rates and rations were highest immediately after stocking, declining through autumn to their lowest levels in December and spring. A bioenergetic model underestimated final mass by a factor of two to three for all esocids; predictions for food consumption were better than those for growth but still overestimated observed values by 39–52%. Neither behavioral thermoregulation nor incorporation of seasonal energetic content of prey altered predictions (maximum of 2% increase). In contrast, adjustments in metabolic rates to account for differences in season and temperature substantially improved model predictions. Size-selective mortality did not account for the inaccuracies in model predictions. Conversion efficiencies (39–63%) exceeded those previously measured for esocids fed maximum rations, suggesting that model variables should be determined for a range of ration levels. Though used extensively, the predictions of bioenergetic models should not be accepted until the models have been subjected to additional field verification.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0230:FCAGOT>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor