摘要:

Sectioned sagittal otoliths were used to determine ages of vermilion snapperRhomboplites aurorubenscollected from the South Atlantic Bight (SAB) by trawl, trap, and hook-and-line gear during 1979–1993. Annulus formation, validated by marginal increment analysis of ages 1–8, occurred from June to August, the peak spawning period for vermilion snapper. Ages ranged from 0 to 12 years for each sex. No significant difference was found for size at age between males and females. The von Bertalanffy growth equation for vermilion snapper taken during 1979–1981 was TLt= 562{1 – exp[–0.202(t+ 0.117)]}, where TLt= total length (mm) at age andt= age in years. The length–weight relationship wasw= 2.147 × 10−5TL2.899, wherew= whole fish weight in grams. Weighted mean back-calculated lengths at age, compared by analysis of variance for five 3-year periods, declined from 1979–1981 through 1982–1984 to 1985–1987. but did not change significantly during 1985–1993. The temporal decrease in size at age did not appear to result from gear selectivity, sampling strategies, or the varying depths and latitudes of sampling areas, but reflected changes in growth that may have been caused by overfishing. In general, caution should be used when growth parameters derived from an overfished population are used to evaluate the biological impacts of fisheries management actions.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0181:AGATCI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Isozyme variation and fluctuating asymmetry at different ages of Atlantic salmonSalmo salarwere analyzed for hatchery and wild stocks. Significant age-related decrease of fluctuating asymmetry was detected in wild stocks but not in hatchery stocks. Natural selection may act against phenotype asymmetry, or some trait associated with asymmetry, in wild but not in hatchery populations. Heterozygosity did not vary significantly with fish age in most cases, suggesting the lack of association between heterozygosity and asymmetry.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0194:FAAIVI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Fish assemblages and environmental variables were evaluated from 37 least-disturbed, 1st- through 6th-order streams and springs in the upper Snake River basin, western USA. Data were collected as part of the efforts by the U.S. Geological Survey National Water Quality Assessment Program and the Idaho State University Stream Ecology Center to characterize aquatic biota and associated habitats in least-disturbed coldwater streams. Geographically, the basin comprises four ecoregions. Environmental variables constituting various spatial scales, from watershed characteristics to instream habitat measures, were used to examine distribution patterns in fish assemblages. Nineteen fish species in the families Salmonidae, Cottidae, Cyprinidae, and Catostomidae were collected. Multivariate analyses showed high overlap in stream fish assemblages among the ecoregions. Major environmental factors determining species distributions in the basin were stream gradient, watershed size, conductivity, and percentage of the watershed covered by forest. Lowland streams (below 1,600 m in elevation), located mostly in the Snake River Basin/High Desert ecoregion, displayed different fish assemblages than upland streams (above 2,000 m elevation) in the Northern Rockies, Middle Rockies, and Northern Basin and Range ecoregions. For example, cottids were not found in streams above 2,000 m in elevation. In addition, distinct fish assemblages were found in tributaries upstream and downstream from the large waterfall, Shoshone Falls, on the Snake River. Fish metrics explaining most of the variation among sites included the total number of species, number of native species, number of salmonid species, percent introduced species, percent cottids, and percent salmonids. Springs also exhibited different habitat conditions and fish assemblages than streams. The data suggest that the evolutionary consequences of geographic features and fish species introductions transcend the importance of ecoregion boundaries on fish distributions in the upper Snake River basin.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0200:FAAECI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Relationships between large woody debris (LWD) and pool area or pool spacing varied with channel slope and channel width for streams in second-growth forests in northwest Washington. Pool spacing (expressed as the number of channel widths between pools) decreased as number of woody debris increased in both moderate-slope (0.02 < slope < 0.05) and low-slope (0.001 < slope ≤ 0.02) channels, but the relationship was stronger in moderate-slope channels. Percent pool was also more strongly correlated with woody debris volume in moderate-slope channels than in low-slope channels. Multiple-regression analyses showed that pool spacing and percent pool were correlated with an interaction term between LWD abundance and channel slope, suggesting that the influence of LWD on pool formation changes with channel slope. Analysis of pool-forming mechanisms indicated that low-slope channels are less sensitive to LWD abundance because pools are formed by mechanisms other than LWD when LWD abundance is low. Size of LWD that formed pools increased with increasing channel width, but was not related to channel slope. Percent gravel (proportion of the bed in patches of gravel 16–64 mm in diameter) was best explained by channel slope and channel width, and there was no significant relationship between woody debris and percent gravel. A regression between median particle size of sediment on the stream bed and basal shear stress showed that the relationships among percent gravel, channel width, and channel slope are adequately explained by the channel's capacity to transport particles of various sizes.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0217:RBCCWD>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We investigated the effects of nonmigrant (residual) juvenile hatchery steelhead (anadromous rainbow troutOncorhynchus mykiss) on growth of wild rainbow trout and juvenile spring Chinook salmonO. tshawytschato examine how increased densities of residual hatchery steelhead might affect the growth of preexisting wild rainbow trout and Chinook salmon. We used screened enclosures in a natural stream to examine food utilization and physiological stress, factors that might affect fish growth. The presence of residual hatchery steelhead led to reduced growth of wild rainbow trout (1993:P= 0.019; 1994:P= 0.020) but not of spring Chinook salmon (P= 0.360). Enclosures did not reduce the total number of food items available but did influence the species composition of aquatic and terrestrial invertebrates. The food habits of paired and unpaired fish differed; however, the power of those tests was low. Cortisol level, a measure of physiological stress, did not differ between paired and unpaired fish held in enclosures. Cortisol levels were significantly lower in fish confined for 42 d than in wild fish outside the enclosures at the end of the experiment. Our results suggest that adverse effects on wild rainbow trout growth resulting from high densities (a doubling) of residual juvenile steelhead from hatchery releases may be significant.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0230:EORHRS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Bonneville ciscoProsopium gemmiferare endemic to and found only in Bear Lake, Utah–Idaho. As part of an investigation into life history characteristics of this species of special conservation concern, we examined survival of Bonneville cisco eggs by measuring changes in egg density under natural environmental conditions. Eggs were vacuumed off the lake bottom over a month period in 1992 and 1993. This survey indicated that egg loss was high: fewer than 4% of the eggs remained after 30 d of an incubation period lasting more than 100 d. Thirty percent of this egg loss could be explained by unsuccessful fertilization or improper embryonic development. An exclosure experiment demonstrated, however, that the majority of the Bonneville cisco egg loss was due to fish predation. A second exclosure experiment indicated that predation rates were not affected by changes in egg density. Our results suggested that fish predation on the eggs may determine recruitment success of Bonneville cisco.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0240:TFOBCE>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The metabolic cost of stress increased with the severity of handling in juvenile coho salmonOncorhynchus kisutchexamined via respirometry. Stressed fish had rates of oxygen consumption 39–98% higher than controls. Elevation in oxygen consumption was largely eliminated within 1 h after stress. Oxygen consumption was significantly correlated to both plasma cortisol and lactate concentration in response to a moderate stressor, but no correlation was found after more severe stressors. Fish given exogenous cortisol did not experience an increase in oxygen consumption, so cortisol alone is unlikely to have a major effect on metabolic rate. Whole-body lactate concentration was significantly elevated following stress, reaching levels almost 500% higher than controls. We suggest that metabolism associated with exercise or hypoxia is the dominant source of elevated oxygen consumption following handling.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0248:TERTHS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Quantitative bioenergetic and physiological measurements were made on juvenile rainbow troutOncorhynchus mykissexposed over summer (June–September 1993) to a simulated summer warming scenario of +2°C in the presence and absence of 70 μmol total ammonia/L (nominal; equivalent to 0.013 mg NH3-N/L at 15°C, pH = 7.6) to determine the metabolic costs and physiological consequences associated with their growth in a warmer, more polluted environment. With unlimited food, fish exposed to +2°C show better energy conversion efficiency and increased nitrogen retention at a metabolic cost equivalent to the base temperature group. Metabolic fuel use appears to have been optimized to support the bioenergetic demands imposed during maximum summer water temperatures. Low-level ammonia enhances nitrogen and energy conversion efficiency by stimulating protein retention, which ultimately results in the most cost-effective growth. However, in the +2°C ammonia treatment, the stimulatory effect of low-level ammonia is lost during mid to late summer due to the greater energy demands when fish are forced to cope with the additional stress of a small further increase in temperature.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0259:TMCAPC>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We collected migrating larvae of walleyeStizostedion vitreumin the Poultney and Missisquoi rivers in 1994 to provide data for developing indices of juvenile walleye abundance. These Vermont rivers drain to southern (Poultney) and northern (Missisquoi) Lake Champlain. We determined the temporal and spatial distributions of larvae migrating from each river by collecting larvae in drift nets at stations below spawning areas. Comparisons of larval densities among dates and time of day within each river were made with standardized densities adjusted for daily changes in discharge in surface migration areas. The greatest standardized larval density at the station near the spawning area in the Poultney River was 2.0/m3at 2055 hours and the greatest density at the down-stream station was 2.0/m3at 0030 hours; peak densities at the downstream station occurred about 3.5 h later than those at the upstream station. In the Missisquoi River, the greatest standardized larval density was 2.8/m3at 2130 hours. Standardized larval densities changed across dates in a quadratic pattern by time of day; quadratic linear regression models fit to observed densities yielded estimates of total walleye numbers during the 12-d migration period in which densities peaked during a 2- to 3-d period. We estimated that 528,000 (95% confidence interval: 307,000–778,000) walleye larvae migrated from the Poultney River and 1,306,000 (891,000–1,727,000) walleye migrated from the Missisquoi River.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0273:TASAOL>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We quantified habitat use, diet, and population characteristics of paddlefishPolyodon spathulain the lower Alabama River, Alabama, in an effort to determine whether juveniles and adults differ in their seasonal use of three types of habitats (oxbow lakes, backwater areas, and channel areas) and to identify differences in population characteristics between fish from the Alabama River and those from other drainage systems. Both juveniles and adults used backwater and channel areas. Paddlefish used backwater areas primarily during summer and fall and channel habitats during winter and spring. Juvenile paddlefish that were present in backwater areas migrated with prespawn adults, whereas juveniles in the oxbow habitat did not. Juvenile paddlefish used oxbow lakes as nursery areas, remaining there until sexual maturity. Paddlefish in the lower Alabama River had shorter life spans than those previously studied further north, suggesting a latitudinal gradient in fish survival. Although fecundity rates were higher, in part compensating for their shorter life span, growth rates were lower than observed elsewhere. Slow growth may result from inhabiting areas where water is warmer than optimal for feeding. However, part of the apparent difference in growth rates may be due to problems in aging paddlefish in previous studies. Paddlefish consumed primarily copepods and cladocerans when available; however, ephemeropteran nymphs were consumed heavily in the channel habitat during winter and spring.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0289:HUDAPS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor