摘要:

Effects of anthropogenic stream degradation on fish assemblages in coastal plain streams of Maryland were investigated by using data from 1989–1993. Fish assemblages, stream physical habitat, and water quality were assessed concurrently at 69 sites. Through the use of habitat and water quality information, two groups were selected from the data set to represent least-impacted streams (N= 16) and most-impacted streams (N= 22). Impacts ranged from agricultural activities involving channelization and riparian destruction to altered hydrologic regime and channel modification related to urban development. Differences in fish assemblages between the two groups indicated that the degraded streams were less diverse and were dominated by a few tolerant taxa, whereas higher-quality sites were characterized by a more balanced assemblage structure and trophic composition, as well as by higher indigenous cyprinid richness and abundance. Various metrics, based on assemblage structure and function under a guild approach, were tested for differences between the high- and low-quality stream groups. The metrics that exhibited the greatest discrimination between groups reflected greater diversity and abundance, a balanced trophic structure, and lower abundance of species considered tolerant to environmental degradation. The most effective metrics included the number of intolerant species present, the number of shiner species, the proportion of silt-intolerant spawners in the assemblage, the proportion of tolerant fishes, and the proportion of insectivorous cyprinids. The metrics that demonstrated ability to discriminate high- and low-quality streams are proposed for development into biological indicators for this region.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0349:FAAIOE>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

I investigated the relationships between year-class strength and selected environmental variables for the migratory population of goldeyeHiodon alosoidesof the Peace–Athabasca delta, Alberta, Canada. Year-class strength was highly variable from year to year. Goldeyes from the 1971 year-class dominated the catch (up to 87%) in the 1970s, and other dominant year-classes (>25% of the catch) developed in 1982 and 1989. The 1985 year-class failed completely. On average, dominant or abundant year-classes (>5% of the catch) occurred about three times per decade. Year-class strength was related to the number of warm days (mean daily temperature >15°C) from May 1 to July 31, the period that covers the time from the spawning migration to the development of a 57-mm, 1.9-g juvenile goldeye (r= 0.57,P< 0.01). The semibuoyant eggs and larvae of goldeyes were present in the delta primarily from May 22 to June 20. A linear relationship was not evident between year-class strength and wind intensity during this 30-d period (r= −0.09). However, dominant and abundant year-classes usually developed in those years when this 30-d period was both warm and calm (wind intensity usually <20 km/h during the day). Year-class strength was not related to discharge of the Peace River, the winter habitat of goldeyes, or to water levels in Mamawi and Claire lakes, the spawning and rearing habitats. Density-independent mechanisms regulate recruitment in the Peace–Athabasca delta population of goldeyes.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0361:RBYCSF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Managers of migratory striped bass stocks that mix along the Atlantic coast of the USA require periodic estimates of the relative contributions of the individual stocks to coastal mixed-stock fisheries; however, to date, a standard approach has not been adopted. We compared the performances of alternative stock identification approaches, using samples taken from the same sets of fish. Reference (known) samples were collected from three Atlantic coast spawning systems: the Hudson River, Chesapeake Bay, and the Roanoke River. Striped bass of mixed-stock origin were collected from eastern Long Island, New York, and were used as test (unknown) samples. The approaches applied were discriminant analysis of morphometric data and of meristic data, logistic regression analysis of combined meristic and morphometric data, discriminant analysis of scale-shape features, discriminant analysis of immunoassay data, and mixed-stock analysis of mitochondrial DNA (mtDNA) data. Overall correct classification rates of reference samples ranged from 94% to 66% when just the Hudson and Chesapeake stocks were considered and were comparable when the Chesapeake and Roanoke stocks were grouped as the “southern” stock. When all three stocks were treated independently, correct classification rates ranged from 82% to 49%. Despite the moderate range in correct classification rates, bias due to misallocation was relatively low for all methods, suggesting that resulting stock composition estimates should be fairly accurate. However, relative contribution estimates for the mixed-stock sample varied widely (e.g., from 81% to 47% for the Hudson River stock, when only the Hudson River and Chesapeake Bay stocks were considered). Discrepancies may be related to the reliance by all of these approaches (except mtDNA) on phenotypic features. Our results support future use of either a morphometrics-based approach (among the phenotypic methods) or a genotypic approach based on mtDNA analysis. We further recommend a conservative strategy of reliance on a single approach in tracking changes in relative contributions of striped bass stocks to coastal fisheries.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0369:AECOSI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Variation in mitochondrial DNA (mtDNA) was examined among 707 red snapperLutjanus campechanusrepresenting 16 samples taken during 3 years from localities in the northern and western Gulf of Mexico. Ninety-two composite mtDNA haplotypes were revealed by 13 restriction enzymes (representing 93 inferred restriction sites). Significant heterogeneity (P= 0.042) in mtDNA haplotype frequencies was detected among the 16 samples; however, homogeneity tests of mtDNA haplotype frequencies between or among samples taken in different years at the same locality and among samples at different localities within the same year, were not significant. No phylogeographic structure of haplotypes was evident, nor were rare haplotypes clustered geographically. Spatial autocorrelations did not differ significantly from those expected when no correlation exists. These findings are consistent with the hypothesis that a single breeding population of red snapper inhabits the northern Gulf of Mexico. Intrapopulational mtDNA diversities, however, differed significantly among samples, suggesting that red snapper in the Gulf may not be drawn from a single population. Red snapper in the Gulf of Mexico may possibly include recently derived populations for which there has been insufficient time for accumulation of significant differences in mtDNA haplotype frequencies.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0386:PSORSF>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We examined mitochondrial control-region haplotype diversity and allelic frequency distributions for three polymorphic microsatellite loci in 541 coastalOncorhynchus mykisscollected from six habitats associated with different levels of human activity and ocean access in southern California. Extensive urbanization, climatic unpredictability, and the accelerated rate of decline in anadromous fish suggested a probable loss of genetic diversity in this area due to habitat fragmentation, geographic isolation, and population bottlenecks. Unexpectedly high levels of genetic diversity were found in southern California populations ofO. mykiss. Haplotype diversity (HS) was highest in anadromous fish (HS= 0.74) and lowest in the Whale Rock Hatchery trout (HS= 0.32). The proportion of variation attributable to population differentiation among habitat groups (GST) was 10%. Haplotype frequencies showed a close relationship between anadromous steelhead and resident rainbow trout from closed habitats (DST= 0.03). Combined microsatellite allelic diversity (at lociOmy77,Omy207, andSsa289) was highest in rainbow trout from closed habitats (88%), and lowest in Whale Rock Hatchery fish (29%). Greatest microsatellite distance (δμ = 17.1) was between anadromous steelhead and reservoir rainbow trout, and closest identity (δμ, = 1.8) was among rainbow trout from closed habitats, hatchery rainbow trout, and reservoir rainbow trout. Analysis of genetic distance measures for both molecular markers showed that considerations of life history patterns and freshwater habitats that retain ocean access remain important factors in the preservation of the unique genetic diversity found in southern California coastalO. mykiss.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0397:MDANMD>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Influences of large-scale abiotic, geomorphic characteristics on distributions of Yellowstone cutthroat troutOncorhynchus clarki bouvieriare poorly understood. We sampled 151 sites on 56 perennial streams in the Greybull–Wood river drainage in northwestern Wyoming to determine the effects of geomorphic variables on Yellowstone cutthroat trout distributions. Channel slope, elevation, stream size, and barriers to upstream movement significantly influenced the presence and absence of Yellowstone cutthroat trout. Wild populations of Yellowstone cutthroat trout were not found upstream of barriers to fish migration, at sites with channel slopes of 10% or greater, or at elevations above 3,182 m. Based on channel slope alone, logistic regression models correctly classified presence or absence of Yellowstone cutthroat trout in 83% of study sites. The addition of elevation and stream size in the models increased classification to 87%. Logistic models tested on an independent data set had agreement rates as high as 91 % between actual and predicted fish presence. Large-scale geomorphic variables influence Yellowstone cutthroat trout distributions, and logistic functions can predict these distributions with a high degree of accuracy.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0418:GIOTDO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Most studies of the diel pattern of trout foraging have focused on examining gut fullness at different times of the day. We used radiotelemetry coupled with stomach content and macroinvertebrate drift sampling to compare the diel activity of Colorado River cutthroat troutOncorhynchus clarki pleuriticuswith variation of invertebrate drift and light intensity on six dates during summer 1993 in the North Fork Little Snake River, Wyoming. The percentage of trout active was greater during midday than at night (medians, 100% versus 40%) and active fish had fewer transmitter signal strength fluctuations per minute during crepuscular periods than during the remainder of the day (medians, 8.8 versus 12.3). Light intensity and daytime macroinvertebrate drift rate were significantly correlated with trout activity but 24-h drift rates were not. Stomach samples collected in the afternoon weighed significantly more than samples collected in the morning. Despite declines in daytime drift rate and stream discharge, the diel movement of trout also declined as summer progressed. Drift and diet significantly overlapped on all six dates, but selection occurred for certain taxa, especially terrestrial insects. We believe that Colorado River cutthroat trout in this stream forage primarily during the day in summer and that low light intensities prevented trout from exploiting the nocturnal increase in drifting invertebrates.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0428:IOMDAL>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The demography of breeding populations of the longnose garLepisosteus osseushas heretofore remained unstudied. During the summer of 1992, longnose gars were captured en route to spawning sites in Weaubleau Creek, a tributary of Missouri's Harry S. Truman Reservoir. To characterize the spawners, individual age, growth, and morphometric data were obtained. The spawning population consisted of smaller, younger males and somewhat fewer older, larger females. As expected, Weaubleau Creek spawners exhibited heightened condition values relative to other longnose gar populations assessed outside the breeding season. Females displayed greater backcalculated total lengths at age and higher growth rates than males, with these differences being manifested early in life. Examination of individual yearly growth increments suggested that most longnose gars in Weaubleau Creek were annual spawners. Females made substantial investments of time and biomass in reproduction, as their gonad weight–body weight relationships, fecundities, and spawning-associated weight and girth losses reflected. Males also invested heavily in reproduction, but may have recouped some biomass through postspawning instream foraging. Fish from nearby Truman Dam differed in their sizes, condition, growth, relative gonad sizes, and relative branchiostegal ray sizes, possibly reflecting the impact of earlier maturation associated with abundant forage. A novel approach for assessing breeding participation in fishes is also developed.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0438:DGARAI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Triploid grass carpCtenopharyngodon idellawith surgically implanted radio tags were stocked in two Texas reservoirs, Lake Texana (4.453 ha) and Lake Weatherford (445 ha), then tracked to determine magnitude and seasonality of movement patterns, diurnal changes in movement, and distribution relative to aquatic vegetation. After release, fish quickly became associated with macrophytes. More than 50% of observed movement during the first 3 months occurred within 1 week. Mean home range area was 3,234 ha (SE = 1,190), and mean core use area was 515 ha (SE = 193). Extensive movement was observed during 24-h tracking conducted immediately after release. However, five 24-h tracking surveys that were conducted at least 3 months after release showed little movement after acclimation. Somewhat elevated movement was evident from 0400 to 1200 hours. We conclude that immediately after stocking, an acclimation period with relatively intense movement occurs followed by an extended period of quiescence. Mean duration of the acclimation period was approximately 7 weeks for lake Texana and 8 weeks for Lake Weatherford. Although both lakes in this study contained habitat considerably more heterogeneous than other sites where 24-h radio-tracking of grass carp had been done, individual fish did not appear to take advantage of the opportunity (via diel movement) to forage in different areas. Hence, daylight tracking alone should be sufficient to determine grass carp movement trends.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0467:DAMBOR>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We examined mercury concentration in muscle of walleyeStizostedion vitreumfrom three reaches in Franklin D. Roosevelt Lake, a reservoir on the Columbia River, and from the upper Columbia River, an area contaminated by wastes from metal mining and associated processing activities. Our objectives were to describe the relation between size and age of walleyes and tissue concentrations of mercury and to compare mercury concentrations within a single reservoir system among spatially segregated cohorts. Overall, mercury concentrations in walleye muscle ranged from 0.11 to 0.44 mg/kg (wet weight) and were positively correlated with age, weight, and length of the fish. Mercury concentrations in walleyes varied spatially within the system; the highest concentrations were in fish from the lower and middle reaches of the reservoir. Condition factor of age-2+ fish was inversely related to tissue concentration of mercury and was lower in fish from the lower and middle reaches than in fish from the upper reach. Spatial patterns in condition factor and mercury in walleyes were unrelated to concentrations of total mercury in surficial bed sediments, which ranged from less than 0.05 to 2.8 mg/kg (dry weight). We suggest that the observed spatial differences in the concentrations of mercury in walleyes may be attributed to the fish preferring to spawn and forage in specific areas where the bioavailability of mercury varies due to local differences in the physical and chemical environment.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0477:SHOMBB>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor