摘要:

Bull trout Salvelinus confluentus and other salmonids in the Pacific Northwest are believed at risk of local and regional extinctions because of ongoing habitat loss and fragmentation. Biologists have focused on defining and protecting critical stream channel characteristics, but there is little information regarding the scale or spatial geometry of habitat that may be necessary for the species' long-term persistence. We investigated the influence of habitat patch size on the occurrence of bull trout by determining the presence or absence of fish in naturally fragmented watersheds of the Boise River basin in Idaho. We defined patches of potential habitat for bull trout as watersheds above 1,600 m elevation, a criterion based on the presumed restriction of local populations by stream temperature. We used logistic regression to investigate the possible influence of patch size as well as stream width and gradient on the occurrence of bull trout at reach, stream, and patch scales of analysis. Both stream width and patch size were significant in the models, but individual effects could not be clearly resolved because of collinearity. The predicted probability of occurrence based on patch size alone was less than 0.10 for patches smaller than about 1,000 ha and more than 0.50 for patches larger than about 2,500 ha. Our results support the hypothesis that area of available habitat influences the distribution of disjunct populations of bull trout. An area effect is consistent with the predictions of island biogeography and metapopulation theory, and our work suggests that larger-scale spatial processes may be important to the persistence of species like bull trout.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0285:OOBTIN>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Some aspects of a previously described migratory paradigm for the southern form of anadromous Dolly VardenSalvelinus malmawere investigated with seven 3-year mark–recapture experiments on fish that used lakes in eight watersheds as their winter residence. Weirs on Kodiak Island, around Prince William Sound, and near Juneau, Alaska, were used to capture Dolly Varden as they emigrated to the sea each spring. Dolly Varden (≥200 mm fork length) were individually marked during the first year of each experiment (1989 or 1990), and log-linear models of their capture histories were used to estimate probabilities of capture during the second year (1990 or 1991). Our observations on timing of spring emigration and dispersal of Dolly Varden at sea confirm observations from earlier studies. Our results support the paradigm that Dolly Varden home to the same lacustrine watershed when overwintering in fresh water, as more than 98% of the recaptured fish did so. Our results contradicted the paradigm that Dolly Varden return to lakes each fall, for across study populations, 14–58% failed to return. The most probable explanation for this anomalous behavior is that some Dolly Varden spend the winter at sea. Differences in maturity, size, and growth of Dolly Varden and timing of their entrance into salt water during spring emigration were excluded as causes of this anomalous behavior.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0297:STOTMH>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Straying results in an exchange of individuals between wild and hatchery salmon populations and is important because it could affect their genetic differences. Understanding what factors affect straying could help in the development of procedures for controlling the influence of specific stocks on nearby populations. We explore the effects of release date and the transportation of juvenile Chinook salmonOncorhynchus tshawytschaon straying by adults from two Columbia River hatcheries. Early and late releases from Washougal Hatchery produced much higher straying levels than intermediate release dates, and this pattern was consistent among brood years. Fish reared at Grays River Hatchery and released from Washougal Hatchery strayed significantly more than local (i.e., Washougal) fish of the same brood year and release date. Our results and those from previous studies indicate that the sequence of imprinting events is characterized by the combination of the time at which the fish experience given locations and the physiological state of the fish at that time. Changes in release date and transportation disrupt the sequence and timing of these events, with varying effects on homing. Hatchery rearing and release techniques can sometimes be modified to control straying and minimize the impact of hatchery fish on other hatchery and wild stocks.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0308:FATHOF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We developed a predation index to describe the relative magnitude of predation on juvenile salmonids by northern squawfishPtychocheilus oregonensisthroughout the lower and middle Columbia River and lower Snake River. The predation index was the product of an abundance index and a consumption index. We evaluated various catch indices and found that catch per unit effort best reflected differences among northern squawfish abundances. Northern squawfish abundance was higher in the lower Columbia River than in the middle Columbia or lower Snake rivers and was highest in Bonneville Reservoir and the Columbia River downstream from Bonneville Dam. The consumption index was based on the concept of meal turnover time for a sample of northern squawfish. Variables needed to calculate the consumption index (CI) were water temperature (T), mean weight of the northern squawfish (W), mean number of salmonids in each gut (S), and mean weight of the gut contents (GW): CI = 0.0209·T1.60·W0.27·(S·GW−0.61). Generally, northern squawfish consumption of juvenile salmonids was highest in tailraces downstream from dams and higher in the Columbia River than in the Snake River. Predation on juvenile salmonids was much higher in the lower Columbia River than in the middle Columbia or lower Snake rivers and was usually higher in summer than in spring. Predation was highest in the Columbia River downstream from Bonneville Dam and in John Day Reservoir. The predation index identified areas where predator control efforts can be most effective. Angling for northern squawfish at dams should be concentrated in tailraces. Removal efforts concentrated in the lower Columbia River would have the greatest effect on predation.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0321:IOPOJS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We described and compared population structure, growth, mortality, and reproduction of northernSquawfish Ptychocheilus oregonensisamong four reservoirs of the lower Columbia River and among four reservoirs of the lower Snake River. We also pooled data for comparisons among three larger areas: Columbia River reservoirs, Snake River reservoirs, and the unimpounded Columbia River downstream from Bonneville Dam. Females made up 76–100% of northern squawfish 380 mm fork length or greater in individual reservoirs, and 87–99% of fish 380 mm or greater in the three combined areas. Females lived longer and grew faster than males in all reservoirs and areas and had lower annual mortality rates in all but two reservoirs. Proportional stock density was highest and annual mortality rates were generally lowest in Columbia River reservoirs. Northern Squawfish downstream from Bonneville Dam had a lower mean relative weight and higher relative fecundity (eggs per unit fish weight) than populations in impoundments. Snake River populations had the highest mortality rates but exhibited intermediate values for other population parameters. None of the biological characteristics were strongly correlated with density of northern Squawfish except relative fecundity. Differences in life history traits of northern Squawfish among reservoirs and between free-flowing and impounded reaches underscore the ability of northern Squawfish to adapt to altered conditions. Spatial heterogeneity in population characteristics creates uncertainty regarding the effects and relative benefits of a northern Squawfish management program to reduce predation on juvenile salmonids.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0335:VIBCON>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The use of bioenergetics models in fisheries ecology and management has increased rapidly in recent years, but application-specific information on energy content of fish and their prey has lagged behind. We believe this is because the process of directly measuring energy density is very time consuming. In this paper we present and evaluate a series of general empirical models that predict energy density (J/g wet weight) from fish percent dry weight. Data were gathered from the literature, obtained from cooperating investigators, and measured directly. Least-squares models were derived for all species combined and for orders, families, and species. All models were linear; however, logarithmic transformation was necessary to normalize residuals in the combined model. All models with more than four data points were highly significant (P< 0.002) and had coefficients of determination of 0.76 or greater. The model for all species combined (N= 587,r2= 0.95) was J/g wet weight = 45.29 DW1.507; DW is the percent dry weight of the fish. At all taxonomic levels, energy density models showed a strong positive relationship between energy density and percent dry weight. This relationship, if corroborated, should allow the estimation of seasonal and ontogenetic changes in energy density based solely on percent dry weight data.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0347:EEDOF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

RuffeGymnocephalus cernuus, a percid native to Europe and Asia, is established in the Lake Superior drainage and could have negative impacts on native fish through competition for forage and predation on fish eggs. We investigated the diet of ruffes in the 4,654-ha St. Louis River estuary in May–October 1989–1990 and the feeding periodicity of ruffes in two adjacent habitats during five 24-h periods in summers 1990–1991. Ruffes were primarily benthophagous. Age-0 ruffes fed mostly on cladocerans and copepods in early summer and midge larvae (Chironomidae) in late summer and fall. Adult ruffes less than 12 cm fed mostly on midges and other macrobenthos but also consumed large numbers of microcrustaceans. Adult ruffes 12 cm and larger fed mostly on midges, burrowing mayfliesHexageniaspp., and caddisflies (Trichoptera). Ruffes consumed few fish eggs. Adult ruffes in deeper waters and all age-0 ruffes fed throughout the day as indicated by weight patterns of stomach contents. However, adult ruffes generally moved to shallower waters at night to feed most heavily. Results of this study indicate that ruffes will probably compete with other benthic-feeding fishes such as yellow perchPerca flavescensand trout-perchPercopsis omiscomaycus.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0356:DAFPOR>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Largemouth bass can hatch over a 70-d period, and among fish less than 90 d old, those hatched earlier can grow faster than those hatched later. Because faster growth of age-0 largemouth bass has been positively linked with fish consumption, it has been suggested that faster growth of largemouth bass hatched earlier was also due to higher fish consumption. We determined hatching-date-specific diets and growth of largemouth bass up to about 180 d old, collected in summer and fall 1987 in a North Carolina reservoir. Frequency of fish consumption for age-0 largemouth bass of all sizes tended to decrease as the growing season progressed. Largemouth bass that hatched earlier, however, were piscivorous at a younger age and maintained a higher level of piscivory late in the growing season than did fish that hatched later. Dietary differences that were hatching-date-dependent seemed to be due to seasonal decrease in prey fish availability. The growth advantage for fish hatched earlier was primarily expressed for fish less than about 85 d old. No growth differences related to hatching date were observed among fish older than 85 d. Studies are needed to determine whether the faster growth of fish hatched earlier results in lower mortality and ultimately in greater recruitment.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0370:HDIOAS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Larval sea lampreysPetromyzon marinusbegin to metamorphose into their parasitic phase in July and migrate to the Great Lakes either in autumn, when they immediately feed on fish, or in spring after overwintering in the stream substrate. Survival and growth of newly parasitic autumn migrants (mean weight, 4.18 g) differed significantly between temperature treatments when sea lampreys were held over winter and allowed to feed on longnose suckersCatostomus catostomusat either the maximum available temperature (˜4°C) or normal surface temperature (minimum <1°C) in the Great Lakes during winter. Survival from December 1990 to June 1991 was 60% for the animals held in the warmer water but only 30% for the animals held in the colder water until 23 April. The average increase in weight was 8.23 g for the 35 survivors in the warmer water but only 5.15 g for the 17 survivors in the colder water. Average increases in weight from December to May for sea lampreys at both temperatures were 3.8 to 6.6 times greater than increases reported previously. A newly metamorphosed sea lamprey that migrates to the Great Lakes in autumn could be 2.5 to 3 times larger in June than one that overwinters in the stream substrate, where it cannot feed, and migrates in spring. Hence, autumn migrants may have an advantage in growth and survival over spring migrants, particularly if food supply is adequate in the warmest stratum of the lake during winter.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0380:GASONP>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We evaluated the relative weight (Wr) condition index as a field assessment tool with pumpkinseedLepomis gibbosusand golden shinerNotemigonus crysoleucas, focusing on sources of variability and potential ofWras a predictor of growth, prey availability, and environmental conditions in 10 southern Quebec lakes over 2 years. To allow calculation ofWr, we developed standard weight (Ws) equations for both species, using the regression-line-percentile (RLP) technique. The proposedWsequation in metric units (grams wet weight and millimeters total legnth, TL) for pumpkinseed is log10Ws= –5.179 + 3.237 log10TL; for golden shiner it is log10Ws= –5.593 + 3.302 log10TL. Spatial and temporal variation inWrwas highly significant and largely asynchronous in both species, although spring values were lowest in most lakes. TheWrindex frequently varied with length, prompting us to examine relationships in stock and quality length fish separately. We found little evidence for a relationship betweenWrand growth in either species. PumpkinseedWswere positively correlated with total benthic invertebrate biomass: stock lengthWrwas positively correlated with chironomid biomass, and quality lengthWrwas positively correlated with gastropod biomass. The relative weight of quality length golden shiners was positively correlated with chironomid biomass. Our results and those of other studies suggest that the common assumption of a relationship betweenWrand growth in field populations should be reconsidered, but thatWrcould be cautiously used as a working index of prey availability. We recommend empirical or experimental verification whenWris used as an assessment tool in field populations.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0387:RWWRAA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor