摘要:

Diets of northern squawfishPtychocheilus oregonensis, smallmouth bassMicropterus dolomieu, walleyeStizostedion vitreum, and channel catfishIctalurus punctatusfrom John Day Reservoir were examined to determine the extent of predation on juvenile salmonids during seaward migrations of the salmonids during April–August 1983–1986. Juvenile Pacific salmonOncorhynchusspp. and steelheadO. mykisswere the most important food group (by weight) of northern squawfish – about 67% – but made up smaller proportions of the food of the other predators: channel catfish, 33%; walleyes, 14%; smallmouth bass, 4%. Seasonal changes in diets indicated that northern squawfish preferred juvenile salmonids in May and August (generally the peak period of salmonid out-migration), and switched to prickly sculpinCottus asperwhen numbers of juvenile salmonids declined; walleyes and smallmouth bass showed a preference only for prickly sculpin among the prey fishes analyzed. As judged by dietary composition and prey selectivity, the northern squawfish was the major fish predator on juvenile salmonids in the reservoir; channel catfish also were important predators in the upper reservoir in spring. Walleyes and smallmouth bass were much less important predators on salmonids, and appeared to select subyearling chinook salmon only in August when the distribution of this prey overlapped with that of the predators. Size-selective predation by northern squawfish may also play an important role in reducing survival of the smaller individuals within each run of out-migrating juvenile salmonids.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0405:FOPFOO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Adult northern squawfishPtychocheilus oregonensis, walleyesStizostedion vitreum, smallmouth bassMicropterus dolomieu, and channel catfishIctalurus punctatuswere sampled from four regions of John Day Reservoir from April to August 1983–1986 to quantify their consumption of 13 species of prey fish, particularly seaward-migrating juvenile Pacific salmon and steelhead (Oncorhynchusspp.). Consumption rates were estimated from field data on stomach contents and digestion rate relations determined in previous investigations. For each predator, consumption rates varied by reservoir area, month, time of day, and predator size or age. The greatest daily consumption of salmonids by northern squawfish and channel catfish (0.7 and 0.5 prey/predator) occurred in the upper end of the reservoir below McNary Dam. Greatest daily predation by walleyes (0.2 prey/predator) and smallmouth bass (0.04) occurred in the middle and lower reservoir. Consumption rates of all predators were highest in July, concurrent with maximum temperature and abundance of juvenile salmonids. Feeding by the predators tended to peak after dawn (0600–1200 hours) and near midnight (2000–2400). Northern squawfish below McNary Dam exhibited this pattern, but fed mainly in the morning hours down-reservoir. The daily ration of total prey fish was highest for northern squawfish over 451 mm fork length (> 13.2 mg/g predator), for walleyes 201–250 mm (42.5 mg/g), for smallmouth bass 176–200 mm (30.4 mg/g), and for channel catfish 401–450 mm (17.1 mg/g). Averaged over all predator sizes and sampling months (April–August), the total daily ration (fish plus other prey) of smallmouth bass (28.7 mg/ g) was about twice that of channel catfish (12.6), northern squawfish (14.1), and walleyes (14.2). However, northern squawfish was clearly the major predator on juvenile salmonids.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0421:ROCOJS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We used mark-recapture and catch-per-unit effort data to estimate abundances and distributions of three potential predators on juvenile salmonids migrating through John Day Reservoir in 1984–1986. The northern squawfishPtychocheilus oregonensiswas the most abundant predator (estimated population: 85,316), followed by smallmouth bassMicropterus dolomieu(34,954) and walleyeStizostedion vitreum(15,168). Because of uncertainty in sampling and assumptions of the mark-recapture estimator, the combined abundance of these three predators could lie between 50,000 and 500,000. We believe, however, that bias is probably negative, and that any errors should result in conservative estimates. Northern squawfish were common reservoir-wide, but large concentrations occurred immediately below McNary Dam near the head of John Day Reservoir. Walleyes were largely restricted to the upper third of the reservoir, whereas the number of smallmouth bass increased progressively downriver. As judged by abundance and distribution, northern squawfish have by far the greatest potential for predation on juvenile salmonids. We also expect predation to be unevenly distributed in time and space as a result of variations in the number and distribution of predators.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0439:AADONS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

–We estimated the loss of juvenile salmonidsOncorhynchusspp. to predation by northern squawfishPtychocheilus oregonensis, walleyes Stizostedion vitreum, and smallmouth bassMicropterus dolomieuin John Day Reservoir during 1983–1986. Our estimates were based on measures of daily prey consumption, predator numbers, and numbers of juvenile salmonids entering the reservoir during the April–August period of migration. We estimated the mean annual loss was 2.7 million juvenile salmonids (95% confidence interval, 1.9–3.3 million). Northern squawfish were responsible for 78% of the total loss; walleyes accounted for 13% and smallmouth bass for 9%. Twenty-one percent of the loss occurred in a small area immediately below McNary Dam at the head of John Day Reservoir. We estimated that the three predator species consumed 14% (95% confidence interval, 9–19%) of all juvenile salmonids that entered the reservoir. Mortality changed by month and increased late in the migration season. Monthly mortality estimates ranged from 7% in June to 61% in August. Mortality from predation was highest for chinook salmonO. tshawytscha, which migrated in July and August. Despite uncertainties in the estimates, it is clear that predation by resident fish predators can easily account for previously unexplained mortality of out-migrating juvenile salmonids. Alteration of the Columbia River by dams and a decline in the number of salmonids could have increased the fraction of mortality caused by predation over what it was in the past.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0448:ELOJST>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A synthesis of information describing the trophic basis for production of marine fishery yield along the east coast of the USA from New York through Georgia is presented. It includes a documentation of the species composition and magnitude of fishery harvest, a delineation of the major food chains, and an estimate of the flow rates of organic matter through populations of yield species. In order to place the information on fishery food webs inappropriate context, we related it to primary production within the system and trophic structure of other systems that have been described. We conclude that (1) algal production is inadequate to support the existing system, and vascular plant production is required; (2) detritus, a frequent dietary constituent, retains at least 42% of the organic material from which it was derived, when it is ingested; (3) the system efficiently converts available organic matter to harvested species through direct paths; and (4) evaluations of fish production in this system may be advanced most rapidly by research on detritus production and use, species composition and diets of forage fish, and mortality rates of both forage fish and prerecruits of yield species.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0459:EMOTTB>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We observed young coho salmonOncorhynchus kisutch, steelheadO. mykiss, and DollyVarden Salvelinusmalma in a second-order stream on Prince of Wales Island, Alaska, to assess differences between species in habitat use and response to cover and predators. Habitat use by subyearlings of the three species differed primarily in depth of water and position in the water column. Coho salmon selected the relatively deep areas of the small stream; steelhead were more evenly spread across the bottom, regardless of depth; and Dolly Varden were close to the bottom in water less than 20 cm deep. All three species selected lower positions in the water column in pools without cover than in pools with riparian or instream cover. We detected no shift in habitat use in response to fish predators.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0474:SHUBYS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Subyearling coho salmonOncorhynchus kisutchand steelheadO. mykisswere placed together and separately in laboratory stream channels to assess their habitat use, interactions, and response to cover and predators. We studied the fish in six replicated riffle-pool-riffle units in the laboratory channels during 12 trials of 7 d each. In all test situations, we allowed the fish to emigrate from the test units. More fish remained in the units of the laboratory streams when both species were together than when either species was alone. The presence of larger fish (potential predators) caused both species to change habitats, regardless of cover available, and many left the test units or were eaten. Coho salmon used mainly the pools, whether stocked alone or together with steelhead; steelhead used both the riffles and pools when alone but shifted slightly toward increased use of the riffles when both species were present.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0486:HUBSAC>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Incidence of black spot disease was measured qualitatively in fish collections from 10 stream systems around Toronto, Ontario. Individuals in 18 of 49 fish species were found with black spot infections; they included representatives of Salmonidae, Catostomidae, Cyprinidae, Centrarchidae, and Percidae. Fishes in the families Petromyzontidae, Umbridae, Ictaluridae, Gasterosteidae, and Cottidae were all collected in substantial numbers but were never observed with black spot. Measures of stream size, gradient, riparian forest, and urbanization were each significantly correlated with black spot incidence for at least four fish species. These data suggest that in southern Ontario streams, habitat degradation accompanying agricultural and urban development is associated with increased incidence of black spot in a variety of fish species. The data also support informed and cautious use of measures of black spot incidence in multivariate indices of stream health, such as the index of biotic integrity.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0494:OAECOB>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Piscivorous fish are size-selective predators. Although sizes of prey selectively ingested by piscivores traditionally have been measured in terms of prey length relative to predator length, the relationship between prey body depth (measured dorsoventrally) and piscivore mouth gape may be a more appropriate measure of prey size selection. In 2-d feeding trials with three sizes of largemouth bassMicropterus salmoides, I offered various sizes of shallow-bodied fathead minnowsPimephales promelasand deep-bodied pumpkinseedsLepomis gibbosusin assemblages of one or both species. All sizes of predators preferred pumpkinseeds with body depths well below the maximum size ingestible. Small predators also preferred fathead minnows with body depths below the maximum size ingestible, whereas intermediate and large predators selectively ingested the largest fathead minnows offered. Largemouth bass never ingested prey of body depth greater than their own external mouth width. Although lengths of selectively ingested fathead minnows and pumpkinseeds differed, largemouth bass showed highest preferences for prey of similar body depths regardless of taxonomic identity. These results suggest that, in addition to setting constraints on maximum sizes of prey that can be ingested by piscivores, the relationship between prey body depth and piscivore mouth gape may also be important in selection of prey within the range of ingestible sizes. Therefore, body depth may be more useful than the traditional measure of prey length as a common measure for examining prey selection by gape-limited piscivores over a wide array of prey species.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0500:EAOPSB>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The relative weight (Wr) index is commonly used to assess fish condition. However, little is known about the relationship ofWrto physiological condition. Whole-body proximate analysis quantifies the general chemical composition of fish but is impractical and too costly for large-scale application to natural populations. Relative weight may offer an alternative method to estimate body composition. We raised juvenile striped bassMorone saxatilisand hybrid striped bassM. saxatilis♀ ×M. chrysops♂ under controlled conditions for a 12-week period and then determined their proximate compositions. Analysis of relationships betweenWrand proximate components indicated thatWrmay be used for estimating body composition and gross energy in juvenile striped bass and hybrid striped bass;Wrwas correlated with percent crude fat, crude protein, ash, visceral fat, and ash-free dry-weight gross energy. Additionally,Wrwas correlated with relative growth and the change in total length for the experimental period. Reserve energy (visceral fat) predicted fromWrmay provide a measure of overwintering fitness and suitability of juvenile striped bass and hybrid striped bass for stocking.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0509:RORWTP>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor