摘要:

The physical habitat simulation model (PHABSIM) produces curves showing the relation between flow and habitat that are often used as evidence for decisions on the management of water resources. The curves show values of “weighted usable area” (WUA) over discharge. Minimum confidence intervals for the curves can be developed with the bootstrap method if transects are randomly located within sampling units. This is illustrated with bootstrap simulations that develop minimum confidence intervals for several model rivers, defined in terms of sampling procedures and values of WUA for juvenile chinook salmonOncorhynchus tshawytschaat 15 transects on the Feather River, California. The simulations show that the chance location of transects in PHABSIM studies can introduce such great uncertainty into the resulting curves of WUA over discharge that the curves can be meaningless. Therefore, it is crucial that confidence intervals be developed for curves of WUA over discharge before PHABSIM results are presented to decision makers.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0458:LISMCI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

We evaluated the relative importance of energy depletion and osmoregulatory stress as possible mechanisms regulating overwinter mortality of age-0 white perchMorone americana. Fish used less energy, took up more water, and had much higher mortality at 2.5°C than at 4.0°C. Mortality, energy use, and water uptake were all related to body size. Relationships of empirically derived endurance time (ET, days to 50% mortality) to body mass were allometric with weight exponents of 0.29 at 2.5°C and 0.77 at 4.0°C. Theoretically derived weight exponents were 0.82 for ET models based on starvation and 0.18 for models based on osmotic mechanisms. The theoretical and empirical models suggest that overwinter mortality of white perch is caused primarily by starvation at 4.0°C and by osmoregulatory dysfunction as well as starvation at 2.5°C.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0466:NTCOOS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Habitat for young-of-the-year rainbow troutOncorhynchus mykisswas enhanced in a fourth-order stream during August–October 1991 by the addition of wooden structures that simulated accumulations of fine woody debris (FWD). The experiment represented a two-factorial design with the presence or absence of FWD bundles and time since debris introduction as factors. Immediately after FWD placement, fry density, individual biomass, fry condition factor, and total fry biomass were similar in treated and untreated sites. As the experiment progressed, density and total fry biomass significantly increased at treated but not at untreated sites. Individual biomass and condition factor did not differ between treated and untreated areas, and they were affected only by time since FWD placement. Because individuals at treated and untreated sites were the same size, added FWD did not affect an individual's net rate of energy gain. Rather, we hypothesize that the FWD provided structurally complex habitat that acted as a refuge from predators and as sites from which foraging forays were staged. Adding FWD to a stream can increase carrying capacity for trout fry, and adult population density may increase as a result.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0472:SFWDAI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The hypothesis that brook sticklebacksCulaea inconstansand fathead minnows Pimephales promelas are competitors was tested in field enclosures containing young-of-the-year individuals from both species. Growth was monitored for 6 weeks, then final weights and gut contents were examined. Fathead minnows were relatively unaffected by brook sticklebacks. Neither dietary composition nor growth was affected in enclosures containing only fathead minnows or a combination of fathead minnows and brook sticklebacks at similar density. The presence of fathead minnows did, however, stimulate growth of brook sticklebacks; this was possibly related to the relatively higher mortality of fathead minnows within the jointly occupied enclosures and the resulting reduced absolute density of fish. The diet of brook sticklebacks also became more diverse in the presence of fathead minnows. In enclosures containing only sticklebacks, the fish consumed primarily copepods. These data demonstrate that growth of brook sticklebacks may be sensitive to both intra- and interspecific competition. This apparent sensitivity of growth to the presence of fathead minnows may account for the observed spatial distribution and migratory habits of brook sticklebacks.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1996)125<0480:IBYOYF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0002-8487    

DOI:10.1577/1548-8659-125.3.486

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor