摘要:

Invertebrate population changes were traced during 1966–1968 in Emmaline Lake, Colorado, after removal in 1964 of a population of stunted brook trout. Species composition of the zooplankton changed greatly after fish removal; in the absence of fish predation, large species were dominant. Populations of mud dwelling midges increased after fish removal; in the absence of fish predation, population regulation appeared to occur through density-dependent larval mortality. Insect emergence over rocky areas was highest in the second summer after fish removal, following increases in periphyton production. In 1968, the lake was restocked with yearling cutthroat trout that fed primarily on midge pupae and Daphnia middendorffiana, and doubled in weight during the first summer in the lake. Growth efficiency of the trout was estimated to be 10–30%. Less than half of the daily ration was present in trout stomachs at any time, as judged from observed growth rate and potential growth efficiency. A computer simulation model of the fish production system suggested that yield and optimum management policy (stocking rate and harvest rate) are most strongly affected by the quantities of terrestrial insects available to fish. Optimum stocking rate is apparently much lower than that which would maximize total invertebrate yield to fish.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1973)102<675:PPOAAL>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

Primary production and limiting nutrients were studied by14C techniques in a small, shallow, subalpine lake. There was no relationship between productivity at any depth and light intensity at that depth. Samples taken near the lake bottom always had higher productivity than samples taken near the surface, probably due to more optimal nutrient conditions. Nutrient enrichment experiments support this hypothesis, since sediment extract and ethylenediamine-tetraacetic acid were always effective in enhancing productivity. The effects of other nutrients and nutrient combinations were less consistent, and tended to change through the summer. A large number of significant three, four and five factor interactions in midsummer indicated that the nutrient requirements of the algal community were most complex at this time. Although retention time increased through the summer from 10 to 71 hours, productivity tended to more closely parallel water temperature.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1973)102<698:PPALNI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

The distribution and limnetic density of five species of Chaoborus larvae were determined in 26 lakes of the Matamek River System, Québec. The distribution of C. americanus is closely related to the absence of fish while C. punctipennis is associated with fish populations. The distributions of C. trivittatus and C. flavicans appear independent of the presence or absence of fish, but C. flavicans reaches its greatest density in the three lakes with the largest individual basins. A probable new species or subspecies of the subgenus Scadanophasma was found in three lakes. The standing crop of limnetic Chaoborus larvae is higher in lakes without fish than with fish.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1973)102<707:TIOFOT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

Hemlock Lake, a eutrophic and meromictic Michigan lake, was artificially aerated by hypolimnetic aeration. This aeration system involved a special aeration tower and compressed air injection. Hypolimnetic oxygen concentrations increased from zero to saturation during aeration. Thermal stratification was gradually reduced by the aeration, but the lake remained thermally stratified for 10 weeks during aeration. Before aeration, rainbow trout (Salmo gairdneri Richardson) were limited to shallow depths by the anaerobic hypolimnion. They distributed to the deepest depths soon after aeration began and occupied the entire lake during artificial aeration.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1973)102<715:EOAHAO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

Travel time of adult sockeye salmon (Oncorhynchus nerka) through the Karluk River, Alaska, was determined from fish tagged with Petersen disks about 2 miles (3 km) inside the river mouth and timed as they reached a weir at Karluk Lake, 21 miles (34 km) upstream. Migration time to the weir averaged 7 days for spring run and l0 days for fall run fish. The influence of three factors on travel time was determined by multiple regression analysis. Most important was time of season, followed by number of fish and rainfall.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1973)102<723:TTAIFF>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

Landlocked salmon, Salmo salar, were introduced into Schoodic Lake, Washington County, Maine in 1960. From 1963–70 we studied nine groups of stocked salmon to obtain information on survival, standing crops, the salmon sport fishery, and population density-catch relationships. Average survival from age I+ to age II+ (four groups) was 47.9%. Average survival from age II+ to age III+ (five groups) was 53.1%. Average survival from age III+ to age IV+ (three groups) was 23.9%. Average survival from age IV+ to age V+ (four groups) was 14.2%. Few salmon survived beyond age V+. Annual survival, excluding fishing mortality, for four groups of young salmon ranged from 26.4% to 61.6%. Survival from planting to 6 months at large for one group was 72.6%. Annual survival after death from all causes ranged from 17.6% for one group of salmon from age III+ to age IV+ to 73.1% for one group of salmon from age II+ to age III+. Numerical annual standing crops from 1964–69 computed by the Petersen method ranged from 4.0 ± 1.0 to 13.8 ± 2.0 fish per ha. Weight standing crops from 1964–69 ranged from 2.5 ± 0.4 to 3.4 ± 1.0 kg per ha. Catch per angler hour by sport fishing ranged from 0.036 in 1969 to 0.229 in 1967. Annual mean number of salmon checked was 164. Salmon creeled averaged 38.6 ± 0.5 cm in total length and 0.5 ± 0.04 kg in weight. Based on an estimated 75.0% census, mean numerical yield was 1.4 fish per ha. Mean weight yield was 0.7 kg per ha. Of 12,107 salmon stocked, 8.6% were subsequently checked in angler's creels. Salmon stocked at age I+, age I, and age 0+ yielded returns of 14.3%, 8.9% and 5.4% respectively. Mean effort per ha per year was 6.9 angler hours. There is a linear relationship (1964–69 data) between population density expressed as numbers per ha and numbers per ha captured by fall trap netting. There is also a linear relationship between population density expressed as numbers per ha and catch per angler hour of all salmon the following fishing season. Indications are that management of small lakes such as Schoodic for salmon can be a fruitful management practice.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1973)102<728:PDOHLS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

This study was undertaken to evaluate the role of cannibalism in determining year class strength of walleyes. From mid-July 1969 to May 1970, I monitored the abundance of young walleyes by trawling and examined stomachs of adult walleyes collected in trawls and gill nets. Number of young walleyes consumed was estimated from occurrence in adult walleye stomachs, digestion rates, and estimated number of adults. Daily consumption ranged from 0.044 young walleyes per adult in August to 0.002 during the winter. Monthly cannibalism, estimated by the multiplication of daily consumption by the number of days and the number of adult walleyes, varied from 1,053,000 young in August to 240,000 during the winter. Cannibalism declined proportionally with abundance of young walleyes. Overwinter mortality rates in 1969–1970 were highest for small young-of-the-year walleyes because adult walleyes were size-selective in preying upon young.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1973)102<739:CAAFIF>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

We assessed the effects of angling and planted trout on the abundance of wild juvenile steelhead trout in a rearing stream with underwater censusing of abundance and angling for steelhead in sections with and without planted trout. A large proportion of the juvenile steelhead were removed by angling. The presence of hatchery reared, catchable-size rainbow trout did not affect the angling harvest of juvenile steelhead trout. Angling reduced the abundance of juvenile steelhead in the catch-remove study sections but did not alter the numbers of juvenile steelhead in catch-release study sections. Partial recolonization of fished-out areas occurred. Angling was selective for larger juvenile steelhead in the test sections, but had no detectable effect on the average size of fish in subsequent samples because fished-out areas were recolonized by fish of the same size as those originally removed. Differences in fish size and habitat preferences reduced interactions between hatchery rainbow trout and juvenile steelhead trout. Hatchery trout released into study sections slightly altered the distribution of juvenile steelhead trout.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1973)102<745:TEOAAH>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

The long-term survival of fin-clipped and unmarked rainbow trout was studied in Castle Lake, California. The results of this study confirmed the generally held belief among fishery workers that fin removal has a serious detrimental effect on fingerling salmonids. Moreover, the relative magnitude of this effect for each of the seven fins that could be removed was determined; viz.: (1) removal of the adipose fin may reduce survival by as much as 50%, (2) removal of a ventral fin may reduce survival by as much as 60 to 70%, (3) removal of a pectoral or dorsal fin may reduce survival by as much as 70 to 80%, and (4) removal of the anal fin may be no worse than removal of the pectoral or dorsal fins, but can have an inconsistent effect. The absence of a single fin did not reduce significantly the rate of growth of the members of a group possessing that mark.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1973)102<753:EOFROS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor

摘要:

Gastric evacuation of a single meal of zooplankters by young yellow perch was about half as fast as that of a similar meal under conditions of continuous feeding. Time for gastric evacuation of a single meal of 150 to 200 daphnids by 60-mm perch at 15 C was 12 hours compared to only 6 hours for a similar meal under conditions of continuous feeding. Likewise, 30- to 40-mm perch fed 10 daphnids at 22 C required 6.5 and 1.5 hours respectively for single and multiple meals.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1973)102<759:EROYYP>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1973

数据来源: Taylor