摘要:

In recent years, recruitment of walleyes Stizostedion vitreum vitreum in Claytor Lake, Virginia, has resulted from both natural reproduction and periodic stockings of age-0 fish from the midwestern United States. Malate dehydrogenase (MDH) allele frequencies of six walleye cohorts were assessed by starch gel electrophoresis. Augmented cohorts were found to possess MDH allele frequencies significantly different from unstocked cohorts, and both augmented and unstocked cohorts differed in allele frequencies from the juvenile fish that had been stocked during that period. Success of supplemental stocking was evaluated by quantifying shifts in cohort allele frequencies due to the stocking of juvenile fish with allele frequencies different from resident fish. Supplemental stocking of juvenile walleyes contributed an average 67% of year-class strength to augmented cohorts in Claytor Lake during 1976–1979. This investigation demonstrates the utility of genetic tags for evaluating stocking efficiency, even in situations where supplementally stocked fish do not possess unique alleles or phenotypes.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<457:UOGTTE>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

We assessed the merits of using Floy anchor tags, machine- and hand-implanted coded-wire tags, and modified Carlin or Swedish trailer tags on chinook salmon Oncorhynchus tshawytscha of at least 15 cm in fork length. Tagged and control fish were released into a landlocked lake. Estimated tag-loss rates were low (2–5%) for each of the tags tested. The tags did not appear to have any significant effect on growth and survival of fish in the lake over periods of up to 2 years.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<464:AEOFTS>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

A small, second-order stream in the southern Appalachians was sampled every 2 months from September 1978 to October 1979. The 1.5-km study segment was divided into 50, 30-m sections grouped into three areas: A downstream area with only rainbow trout Salmo gairdneri; a middle, mixed-trout area; an upstream area with predominantly brook trout Salvelinus fontinalis. Although a few fish of both species exhibited substantial movements, the majority of fish moved less than 30 m either upstream or downstream. Growth rates of both species were approximately equal until the spring of their second year, when rainbow trout outgrew brook trout and thereafter maintained a size-at-age advantage. Rainbow trout, particularly the 1978 cohort, dominated trout production in the stream. Even in the brook trout area, where the density of 1978 cohort brook trout was twice that of 1978 cohort rainbow trout, rainbow trout outproduced brook trout by 1.20 g/m2to 1.14 g/m2. Declining mean biomass of older fish of both species indicates high winter mortality. This, accompanied by slow growth of older fish, resulted in very few fish of either species entering the legal fishery.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<469:GAPOSB>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The mysid shrimp Neomysis mercedis is a major prey of striped bass Morone saxatilis in the inland delta and estuary of the Sacramento and San Joaquin rivers, California. Its abundance during 1968–1981 was highest between 1.2 and 4.6‰ surface salinity. Cross-delta flow of water to large pumping plants and shallow river channels with high current velocities limited the upstream extent of the shrimp. The population shifted spatially in response to salinity changes caused by variations in river outflow. Annual July to October abundance indexes were highest from 1968 to 1975, and lowest during the drought years 1976 and 1977. Regression analysis showed that population size was negatively related to salinity intrusion and positively related to the abundance of the copepod Eurytemora affinis, an important food item of the shrimp. High N. mercedis populations appear dependent on adequate food supply and minimal salinity intrusion into the western delta.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<476:FRAADO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The hypothesis that young of the year of two sympatric morphs of tui chub Gila bicolor were trophically indistinguishable was tested in Pyramid Lake, Nevada. Based on gill-raker counts, young-of-the-year tui chubs longer than 25 mm fork length could be separated into distinct morphs, G. b. obesa (fewer gill rakers) and G. b. pectinifer. Undesignated juveniles shorter than 26 mm, collected from depths 1 m and less, ate primarily zooplankton plus small quantities of macroinvertebrates. Among G. b. obesa, consumption of macroinvertebrates, principally chironomids, rose to 41% for fish 26–50 mm long and to 62% for fish 51–75 mm long. Among G. b. pectinifer, diets of fish 26–50 mm and 51–75 mm long contained 93 and 100% zooplankton, respectively. As young of the two morphs grew larger, their gill-raker distributions became nonoverlapping. Divergence in food selection accompanied the shift in numbers of gill rakers. Our results suggest that sympatric morphological variants of polytypic fishes like tui chub should be treated as functionally distinct species for fishery-management considerations.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<486:FPBYOT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Food-habit, niche-breadth, and diet-overlap analyses were conducted for larvae of American shad Alosa sapidissima and blueback herring Alosa aestivalis collected from the Connecticut River from June 3 to July 15, 1981. River zooplankton densities (numbers˙m−3were used to assess the influences of prey availability on niche-breadth and diet-overlap indices for the species. Niche-breadth values were consistently higher for blueback herring than for American shad larvae. American shad fed mostly on the less-abundant crustaceans and immature insects, whereas blueback herring larvae usually utilized the numerically dominant rotifers. The cladoceran Bosmina sp. was utilized extensively by American shad of all sizes and by 13–16-mm blueback herring larvae, and was the only prey for which interspecific competition between the larval predators might occur. The mean mouth gape of American shad larvae was always larger than that of blueback herring larvae at a given length, and American shad larvae of all sizes generally selected the larger cyclopoid copepodites and chironomid larvae. The diet-overlap indices varied over time, but were generally higher among length groups within species than between species, suggesting that intraspecific competition for food may be more severe than interspecific competition.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<498:FEOCLO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Largemouth bass Micropterus salmoides are the dominant top carnivores of many North American lakes and reservoirs and are very popular sport fish, but the actual behavioral mechanisms of their feeding are still poorly known. In laboratory experiments we broke predation into its component parts: Location, pursuit, attack, and handling of prey. The distance at which largemouth bass can locate forage fish increases with prey size, with prey motion (when prey are small), and with light intensity. In the pursuit phase of the predation cycle, largemouth bass are more likely to choose prey with large apparent size, closer proximity, or greater motion. When bluegills Lepomis macrochirus were the experimental prey, the number of attempted attacks by largemouth bass before the prey was ingested increased with bluegill size, within broad limits. At high light intensities bluegills can locate modest-size largemouth bass (29 cm total length) long before the predators locate them, but at low light intensities, the advantage is reversed.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<508:PFBOLB>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Distribution and growth of rainbow smelt Osmerus mordax larvae are described from samples collected in eastern Lake Michigan during 1978–1981 with plankton nets and benthic sleds deployed in water 1–15 m deep. Rainbow smelt larvae less than 25.5 mm total length were caught from May to early August, whereas young of the year 25.5 mm and larger occurred from July to September. Newly hatched larvae were found mostly during May; however, some hatching occurred in late June or early July, apparently due to slower incubation of eggs in deep cooler water. After hatching, rainbow smelt larvae were distributed in shallow water for a short period; from June to early August larvae were widely dispersed. Larvae concentrated inshore in late August. They generally were found at a few random depth strata from May to early August. In late August larvae concentrated near bottom. Larval rainbow smelt were most common at water temperatures of 10 to 16 C. Rainbow smelt averaged from 5.3 to 6.1 mm in May; they grew to a mean length of 15.7 mm after 1 month and to 36.5–41.1 mm after 3 months.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<517:DAGOLR>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The diagnostic potential of dorsal and anal pterygiophore-interdigitation patterns was examined in larvae of striped bass Morone saxatilis, white bass M. chrysops, white perch M. americana, and yellow bass M. mississippiensis. The number and position of pterygiophores relative to interneural spaces 1–6 and 10–13 and to interhaemal spaces 12–15, as well as total number of dorsal and anal pterygiophores, are characters useful in delimiting larvae of these species. Interdigitation patterns useful in distinguishing yellow bass from white perch larvae were not found; however, these two species may not co-occur.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<525:PPILOF>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The effects of prolonged stream desiccation on development of salmonid eggs were simulated for steelhead Salmo gairdneri and spring chinook salmon Oncorhynchus tshawytscha. Recently fertilized eggs were placed in artificial redds and subjected to controlled water flows in outdoor laboratory channels. Control redds were continuously submerged. “Dewatered” redds were exposed to air; water flowed through the substrate 10 cm below the eggs. Eggs were dewatered 1–4 weeks (steelhead) or 1–5 weeks (chinook salmon) before they were returned to water in hatchery incubators, where hatching success and subsequent fry development were monitored. Several combinations of cobble, coarse sediment, and fine sediment used to cover eggs did not influence egg development, provided the mixtures retained at least 4% moisture by weight. Dewatered eggs hatched sooner than control eggs; faster hatch was associated with higher substrate temperature in exposed redds. Hatching success of dewatered eggs averaged 94% for steelhead (control: 88%) and 76% for chinook salmon (control: 56%) and was not affected by the time eggs had been dewatered. After 8 (chinook salmon) and 8.5 (steelhead) weeks of rearing, juveniles from dewatered and control eggs had grown equally well.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1983)112<532:EOCRDO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor