摘要:

Lake Taneycomo, a 700-hectare hydroelectric impoundment in Taney County, southwestern Missouri, is fed by cool hypolimnetic waters from an upstream reservoir. A popular put-grow-and-take fishery for rainbow trout Salmo gairdneri has become established in Lake Taneycomo, but fishing success and effort decline each fall when oxygen-depleted waters enter the lake. The fishery was examined in detail from June 1978 through May 1980. During this period, catch rates of rainbow trout averaged 0.55 fish/hour, and were influenced by dissolved-oxygen concentration, number of fish available to be caught, discharge rates from the upstream reservoir, angler experience, and water temperature. A decrease of 1 mg/liter dissolved oxygen, between 6.0 and 2.4 mg/liter, reduced catch rates by 0.1 fish/hour. During the fall, a change in catch rate of 0.1 fish/hour can result in a change of 20,000 hours of fishing at Lake Taneycomo. The expected annual economic loss to the Taney County economy due to low concentrations of dissolved oxygen is $358,000 (range, $267,000-$432,000).

ISSN:0002-8487    

DOI:10.1577/1548-8659(1984)113<109:EODDOT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Seventeen paddlefish were tracked in Pools 12 and 13 of the upper Mississippi River during summer 1980 and spring and summer 1981. Interpool movement occurred during spring high-water periods when dam gates were lifted to create a free-flowing river. Habitat use varied by season; selection was greatest for tailwater and channel habitats, although strong association with one backwater slough was evident. Paddlefish often congregated near man-made structures that created eddies and reduced current velocities.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1984)113<125:HUBAPI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Seasonal collections of American eels Anguilla rostrata were made with baited traps at an estuarine and a freshwater site in the Altamaha River, Georgia. Estuarine animals were on average shorter, lighter, and younger than freshwater animals, although growth was faster in the estuary. Both sites were characterized by greater weight gains in spring through fall and lesser weight gains during late winter. Males constituted 36% of sexually differentiated American eels in the estuarine population but only 6% in the freshwater population. Estuarine males grew more slowly than estuarine females. Males and females differentiated sexually at the same lengths and ages, but matured at younger ages in the estuary. Sexually undifferentiated and differentiated fish overlapped considerably in length, weight, and age at both sites. Glass eels were captured in late winter; they were 49–56 mm long and 250–300 days old. Maturing silver eels were caught during late winter-early spring and were 353–587 mm long and 3–6 years old. In general, American eels from the Altamaha River are smaller, younger, and may mature more rapidly than animals at more northern latitudes.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1984)113<132:SAASOA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Chronic turbidity in streams during emergence and rearing of young anadromous salmonids could affect the numbers and quality of fish produced. We conducted laboratory tests to determine the effect of chronic turbidity on feeding of 30–65 mm long steelheads Salmo gairdneri and coho salmon Oncorhynchus kisutch in straight and oval channels. Fish subjected to continuous clay turbidities grew less well than those living in clear water, and more of them emigrated from channels during the experiments.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1984)113<142:EOCTOD>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

ISSN:0002-8487    

DOI:10.1577/1548-8659(1984)113<151:TSLFC>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Oceanic or coastal spawning grounds of fish are often distant from nursery areas. Fish larvae require appropriate currents and sufficient and suitable food during transit to reach the nursery area at the proper time, size, and condition. Meteorologic and oceanographic factors influence food availability and transport direction and time. Annual variation in these controlling factors could affect recruitment success. Certain generalizations can be made that apply to marine and estuarine systems. Reproduction occurs in a selected portion of the species' total range. Spawning often takes place close to gyral, upwelling, or other directional circulations that frequently are associated with major current systems. The coupling of spawning to natural oceanographic transport systems for eggs and larvae is advantageous to a species as long as those systems operate normally. The details of such coupling, and the consequences for eggs and larvae of deviations from usual transport mechanisms, remain poorly understood. Investigation of year-class success requires a clearer understanding of the natural variability and periodicity inherent in these physical processes. Further research is needed to resolve these details, including environmental cues to reproductive behavior and relative importance of passive and behaviorally mediated transport; to statistically analyze atmospheric and oceanographic cycles; and to quantify transport mechanisms for spawner-recruit models and predictions of year-class success.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1984)113<153:OAETOF>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Monthly plankton collection of eggs and larvae of sea bream Archosargus rhomboidalis were made in Terminos Lagoon, Mexico, from February 1980 until April 1981 in order to determine the species' spawning season and area and adult stock size, and to study aspects of its early life history. Spawning occurred from January to July, and was most intense from January to April, when temperature ranged from 21.5 to 29.9 C and salinity from 8 to 38% Major spawning areas were above sea grass beds. The estimate of annual egg production was 8 × 1011. Adult females were considered to be multiple spawners during one spawning season. Fecundity was related to fish length and weight and the relative fecundity was 485 oocytes per gram body weight. The egg production divided by relative fecundity and adjusted for a proportion of 60% females among adult fish gave an estimate of 2,700 metric tons for adult biomass. Larvae are carnivorous, feeding mainly on copepods, and prey size showed a clear relationship to mouth diameter and digestive-tract length of larvae. Larva growth was studied from daily growth increments on otoliths and mortality rate was estimated in relation to larva length and age. Mortality was 35% per day during the first 2 weeks of planktonic life, 17% per day until metamorphosis, then 0.2% per day until age 1 year.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1984)113<166:ELHAAB>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

A scholarly life-history model, applicable to various ontogenies, requires precise definitions of the major periods and their boundaries. The theory of saltatory ontogeny enables one to construct such a model based on natural boundaries between consecutive intervals of development. This theory stipulates that development does not proceed by a continuous accumulation of inconspicuous, small changes but is a sequence of rapid changes in form and function alternating with prolonged intervals (steady states) of slower development during which complex structures are prepared for the next rapid change. These times of rapid changes from one steady state to the next are called thresholds and represent decisive events of life history. Saltation explains some of the most misunderstood events of ontogeny. For example, it explains why only activation should be accepted as the beginning of ontogeny, and why insemination, fertilization, and hatching are not the appropriate clues for timing ontogeny. Similarly, it is argued that according to the definition of the larva period–lasting from onset of exogenous feeding until metamorphosis–not all fishes have larvae. In fishes with an increased endogenous food supply and parental care (increased reproductive cost per embryo), the embryo develops permanent organs directly, bypassing the larva period with its remodelling of temporary structures. Hatching is rarely a developmental threshold. The transition to exogenous feeding, rather than hatching, is the decisive threshold of ultimate survival value.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1984)113<178:ROSDEI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The otoliths of larval fish may be useful data-storage systems if the mechanisms of formation and carbonate deposition are discerned. Striped mullet Mugil cephalus were reared from hatching under controlled laboratory conditions. The start and periodicity of otolith growth increments were examined by light and scanning electron microscopy, and ratios of stable isotopes in otolith carbonate were determined. Otoliths formed their first increment 1 day after the larvae hatched and increment formation continued on a daily schedule regardless of growth rate. Electron microscopy revealed a transition area in otoliths that corresponded to the time of yolk-sac absorption. Isotopic analyses showed that otolith carbonate is deposited in disequilibrium with the ambient water chemistry, in contrast to prevailing theory.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1984)113<186:FASCOL>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Tucker-trawl collections showed that behavior of larval shad Dorosoma spp. and freshwater drum Aplodinotus grunniens was altered by inflow of turbid water into Lake Texoma (Oklahoma-Texas) in two different years. During periods of increased turbidity, larval shad were concentrated in a reduced volume of water near the surface, and larval freshwater drum were distributed throughout the water column in contrast to their normal concentration near the bottom. In 1981 and 1982, greatest decline in abundance of larval shad came after zooplankton density fell below 100 per liter, and during or immediately following an extended period of high turbidity. Nutritional stress resulting from decline in zooplankton abundance and changes in larval-fish behavior during turbid conditions could be one important factor in population dynamics of shad in reservoirs.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1984)113<192:IOTIOV>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor