摘要:

To predict the effects of reduced flows on potential rearing habitat for fish in a large braided river (the lower Rakaia River on South Island, New Zealand), water depth, velocity, and substrate data were collected along transects in two representative reaches at five discharges ranging from 69 to 146 m3/s during 1981–1982. From these measurements and habitat-suitability curves, weighted usable area (WUA) was computed for each of six species of fish. Within both reaches WUA declined with decreasing discharge for each of the native fish species, although variably so in space and time (2–33%), whereas for the two exotic salmonid species there was no consistent and appreciable change. The overall decrease in WUA was attributed primarily to the loss of habitat in minor channels (<1 m3/s). Weighted usable area ranged from approximately 20,000 m2/km of river for juvenile chinook salmon Oncorhynchus tshawytscha, which prefer relatively deep, slack water with cobble-bedded substrates, to 80,000 m2/km for the longfinned eel Anguilla diefenbachii, which inhabits a wide range of water depths and velocities, probably because of its ability to live among the interstices of bed sediments. Inclusion of substrate size distribution in the data analysis significantly lowered the amount of WUA for all species (range 15–65%), but had no appreciable effect on the rate of change of WUA with decreasing discharge. For all the branch channels measured (ranges 0.01–76 m3/s and 3–140 m wide), average WUA for six fish species combined was positively correlated with channel discharge and channel width, suggesting that WUA for the whole river would continue to decline with decreasing river discharge below 69 m3/s. Unlike single-thread rivers, braided rivers tend to show (within the general range of base flows) relatively little change in WUA with decreasing discharge, because the loss of habitat in minor channels is offset by the gain of habitat in major channels.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<165:PEORFO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Brown trout Salmo trutta in Vangsvatnet Lake, Norway, include freshwater residents that mature sexually without any sea run and migrants that smoltify and migrate between fresh water and the sea one or more years before maturing. Migrants leave Vangsvatnet Lake during spring and move in coastal waters up to 100 km from the lake outlet before they return to their home river in summer or autumn; older migrants return earlier than younger migrants, sexually mature fish before immatures. Both residents and migrants spawn together in tributaries to Vangsvatnet Lake. Young brown trout (parr) grow in the tributaries and lake; lake dwellers grow faster than stream dwellers. Parr that become migrants at age 2 grow faster than parr that become residents, but parr that become migrants at age 4 and older grow more slowly than those that become residents. Parr that smoltify or mature at a young age grow faster than parr that do so later. Resident males are 2–8 years of age, and 13–47 cm in tip length, resident females 3–10 years and 21–45 cm. Smolts are 2–7 years old and 14–29 cm long. Mature migrants are 3–9 years old; males are 29–67 cm and females 34–67 cm long. Sex-ratios were in favor of males among residents, in favor of females among migrants.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<182:LHPOFR>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Since 1900, the distribution of native brook trout Salvelinus fontinalis has shrunk in the southern Appalachian Mountains area. Initial reductions were caused by logging and heavy fishing pressure but, in later years, encroachment by exotic rainbow trout Salma gairdneri may have contributed. Historical and current field evidence supports the hypothesis that the modern contraction of the brook trout's range is due to encroachment by rainbow trout. In Great Smoky Mountains National Park, Tennessee-North Carolina, brook trout formerly occurred from headwaters to low-gradient streams near the park boundary. They retain this longitudinal distribution in a few streams today, but only in those lacking rainbow trout. The typical pattern in other streams is for allopatric brook trout to be in upper stream reaches, allopatric rainbow trout in lower reaches, and a zone of sympatry (up to about 3.2 km long) between the two pure populations. Few age-0 rainbow trout occur in zones of sympatry unless adult brook trout are rare, and vice versa. In stream segments with similar physical characteristics, allopatric brook trout and allopatric rainbow trout have similar numerical densities, but the average size of rainbow trout is larger, and rainbow trout have biomasses about 1.8 times greater than that of brook trout. Adult allopatric brook trout occupy main channel habitats, but they occur predominately in peripheral stream areas when sympatric with rainbow trout. We believe the encroachment of rainbow trout is dynamic and continuing in the park and elsewhere in the southern Appalachian Mountains, and that brook trout ultimately will be reduced to a few small inbreeding populations in headwater refugia, and exterminated from many streams, if no management measures are taken.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<195:EOERTI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Young-of-the-year largemouth bass Micropterus salmoides in Lake Opinicon, Ontario, displayed a divergence in size over their first summer. The range in total body lengths was 11 mm when year-0 fish were first captured on June 22–25, and this range increased to 26 mm by September 8–12. The size divergence was not due to a protracted or disrupted spawning period and, instead, appeared to be underlain by differences in diet and prey availability. Diets of small and large year-0 largemouth bass (less than and greater than the cohort mean length, respectively) differed progressively over the summer. Large year-0 fish maintained a diverse diet of which fish prey always constituted 25–30% by volume. In contrast, small year-0 largemouth bass shifted from a diet comprised of zooplankton, aquatic insects, and larval fish in July to one dominated by zooplankton, and including no fish, in September. The diet shift of the small individuals occurred when fish prey became too large to handle. However, some forage fish were always within the manageable size range for large year-0 largemouth bass and, consequently, large individuals were able to maintain fish in their diet. Analysis of the gross energetic value of the diets showed that larger year-0 individuals obtained a higher energy content in their diet, relative to the small individuals.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<204:GDIYLB>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The contingent valuation method was used to estimate the economic value of sport diving around the many petroleum structures located off Louisiana's coast. The average diver derived economic surplus in the amount of $163 (95% confidence interval, $136-$190) annually from this activity. Variation of the mean bid was not statistically affected by interview techniques, purpose of trips, years of diving experience, distance traveled over land and sea, investment in equipment, or average trip costs. The number of trips was the only variable that had a significant effect on the mean bid; however, the number of diving trips depended on income, overland distance to port, and trip cost. The trip cost variable, though significant, was positively signed. A finding of a significant positive relationship between trip cost and number of trips indicates the merit of using the direct estimation technique of contingent valuation.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<214:CVORDA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

In 1982–1983, 15 pairs of captive tessellated darters Etheostoma olmstedi proved to be fractional spawners and produced from two to eight clutches (19 to 324 eggs per clutch; mean = 158) between the last week of April and the first week of August, in northeastern Pennsylvania. Average clutch size for individual pairs ranged from 49 to 204. The total number of eggs spawned per pair ranged from 97 to 1,435 (mean = 727). Intervals between clutches ranged from 5 to 16 d (mean = 7.6) in troughs and pools and from 8 to 26 d (mean = 16.3) in cages in a cool, spring-fed creek. Spawning usually occurred during daylight. Eggs began hatching in 97 h at 25 to 26°C. In 1984, the left ovary of eight fish confined for various durations held from 2,790 to 5,365 eggs of a continuum of sizes; 85.3% of 29,210 eggs were 0.2 mm or less, the size retained after the spawning season. Egg complements from females spawning up to six clutches were virtually indistinguishable from those of prespawning females, indicating continual egg recruitment from the group 0.2 mm and smaller. Fecundity estimates based upon ovarian eggs in prespawners would have been much too high if all eggs had been counted and far too low if only ripe eggs had been included.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<220:FASFOC>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

We present evidence for reduced developmental stability in a hatchery stock of westslope cutthroat trout Salmo clarki lewisi. These fish have a high frequency of two obvious morphological deformities and an unusually high amount of asymmetry at five bilateral meristic traits. We have previously reported that this stock has a reduced amount of genetic variation at 35 isozyme loci compared to the wild population from which it was derived. The loss of genetic variation in this stock apparently has reduced the ability of these fish to develop precisely along genetically determined developmental pathways. We also present the biological rationale and the methods for using fluctuating asymmetry as a diagnostic tool for detecting the effects of the loss of genetic variation in cultured stocks of fish.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<230:DIAAIO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Biochemical genetic variation was found among populations of sockeye salmon Oncorhynchus nerka in the Russian and Karluk river systems in Alaska. Significant differences in allele frequencies of lactate dehydrogenase (Ldh-4), phosphoglucomutase (Pgm-1), and cis-aconitase (Aco) were found between the early and late runs in both the Karluk and Russian rivers, and between fish from the two rivers. The most common allele for Aco in the Russian River fish was lacking in fish from the Karluk River. Gene frequencies were stable between years, except for 1 year in Karluk River fish. Within the Karluk system, there were no significant genetic differences between groups of early-run fish, or between groups of late-run fish. Average heterozygosities (H) fell within ranges reported for other populations of sockeye salmon. Our data suggest that the two runs of sockeye salmon in each river system are now reproductively isolated as a result of natural events.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<236:GDAPOA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Isozyme electrophoresis was used to assess biochemical genetic variation in spawning striped bass Morone saxatilis captured from two tributaries of Kerr Reservoir, Virginia-North Carolina in 1979 and 1980. Only 3 of 56 scorable loci were polymorphic. Average heterozygosity was estimated at 1.6%, similar to measurements made on anadromous Atlantic coast striped bass stocks, but well below typical values for either freshwater or marine fish species. Allele frequencies of polymorphic loci were independent of sex and age, with the exception of Itp, which demonstrated variation among age groups. Allele frequencies for each of the polymorphic loci differed significantly between rivers for collections made in 1979 but not in 1980. It is hypothesized that striped bass exhibit spatial as well as temporal heterogeneity in the distribution of genotypes within spawning rivers, which can influence interpretation of genetic distinctness of spawning groups. The low degree of genetic variability which is resolvable by isozyme electrophoresis appears to limit its usefulness for discriminating among landlocked striped bass of different genetic origins.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<244:EAOGVI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Ecological studies using measures of overlap or similarity often treat these measures as free of sampling error. If sample sizes are relatively small, however, the estimates of overlap may not be accurate, and misleading interpretations may result. Two methods are presented here for estimating the variance of a general weighted measure of similarity. First, an approach based on the multinomial model is discussed. Because the multinomial model is not valid when data are clustered, a second more general approach is given. The more general approach is applicable when the data may be broken into units; in diet analysis, for example, a stomach may be used as a unit. Two examples illustrating the usefulness of the methods are given.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<250:SCOWOM>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor