摘要:

We examined distribution and abundance of small, medium, and large American eelsAnguilla rostratain Virginia streams by comparing observed with expected null-model patterns. At large spatial scales (across drainages or physiographies), densities of small and medium American eels decreased with distance from the ocean, and densities were not strongly or consistently related to local habitat features (e.g., habitat type, abundance of cover, water temperature, density of predators). A mathematical function, analogous to diffusion of particles from a concentrated source, accounted for up to 85% of the variance in densities of small- or medium-sized eels at statewide, physiographic, or river-drainage scales. At smaller spatial scales (e.g., within a drainage in a particular physiography), we found few relations between American eel density and habitat features. Exceptions to this pattern occurred at Coastal Plain sites of the James River drainage, where American eel densities were exceptionally high. Such small-scale, nonrandom patterns may reflect local density-dependent processes that only rarely affect American eel distribution and abundance more than do ubiquitous, large-scale random processes. Parsimonious, large-scale models (e.g., diffusion models) may predict the distribution and abundance of American eels (and other widespread or generalist stream fishes) more reliably than do more typical, small-scale habitat models (e.g., habitat suitability models).

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0789:DAAOAE>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The spatial and temporal patchiness of limnetic fishes is not well understood but has important implications for biological interactions as well as for sampling strategies. We used hydroacoustics to assess the distribution of threadfin shadDorosoma petenensein Lake Norman, North Carolina, a large, multipurpose reservoir. We sampled three transects on four consecutive days and nights in April, July, and October to enable us to characterize threadfin shad on both daily and seasonal time scales. We used a patch recognition algorithm to analyze echo-integrated hydroacoustic data in order to define patches and related patch characteristics (numbers, density, area, and mean depth). Threadfin shad in Lake Norman were patchily distributed and exhibited strong, generally consistent patterns in patch number, fish density, size, and depth. During most surveys we observed 12–16 patches/km with fish densities exceeding twice the average background density, and 1–2 patches/km with fish densities 50 times the average background density. Most patches were small (<50–100 m2in the vertical plane); less than 10% of the area contained 50% of the fish. In October night surveys, patches tended to be larger and less numerous and to have lower fish densities than at other times. Depth distribution of patches varied among seasons and was influenced by temperature, by oxygen concentration, and possibly by vertical distribution of predators and prey. Temporal changes in patch distribution suggested that fish composing the patches were highly mobile, spatially integrating threadfin shad impacts on their zooplankton prey. Large differences in day and night average density estimates in October suggested strong diel habitat shifts by threadfin shad during fall.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0804:SATDOT>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Over 77,000 fish remains from 51 archaeological sites on the central California coast between San Mateo and San Luis Obispo counties, deposited between 6200 B.c. and A.D. 1830, were studied to assess prehistoric species distribution, diversity, and Native American fisheries. Remains were obtained from exposed rocky coastal sites, lagoon–estuaries at Elkhorn Slough and Morro Bay, and the freshwater drainages of the Pajaro and Salinas rivers. On the rocky coast, 58.4% of the remains represented large inshore species, 26.9% were small schooling species, and 11.8% were surfperches (family Embiotocidae). Large inshore species included rockfishesSebastesspp., lingcodOphiodon elongates, kelp greenlingHexagrammos decagrammus, cabezonScorpaenichthys marmoratus, and monkeyface pricklebackCebidichthys violaceus. At Elkhorn Slough and Morro Bay, about half of the remains of marine species represented moderately small schooling species, including Pacific herringClupea pallasi, Pacific sardineSardinops sagax, northern anchovyEngraulis mordax, topsmeltAtherinops affnis, jacksmeltAtherinopsis californiensis, and California grunionLeuresthes tenuis. Surfperches also were common, and specialized local fisheries for flounders or sharks and rays were suggested. Aquatic conditions at Elkhorn Slough were dramatically different from those that exist today. Sites on Elkhorn Slough had both marine and freshwater fishes and showed site occupation when the Salinas River entered the slough and did not follow its present course into Monterey Bay. Sacramento perchArchoplites interruptuswas the most abundant species found at freshwater sites, and remains of extinct thicktail chubGila crassicaudaconfirm its presence in the Pajaro and Salinas rivers. Surprisingly rare are the remains of steelhead (the anadromous form of rainbow trout)Oncorhynchus mykiss. As is the case today, Pacific salmon were apparently absent from central coast streams south of the San Lorenzo River. Presumably the remains reflect local species availability.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0813:PNAFOT>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We examined how condition (weight at length) of rainbow troutOncorhynchus mykissvaried in relation to availability of drifting invertebrates and temperature at two locations over four seasons in the Green River, Utah. Food availability (daytime drift density) varied more than 17-fold across sites and seasons, and rainbow trout experienced an 11°C range in mean monthly temperature. Both rainbow trout gut fullness and condition increased as joint, nonlinear functions of increasing food availability and increasing temperature. Variation in condition decreased with fish size, although condition of intermediate sized fish was most strongly related to variation in food and temperature. Observed relationships between rainbow trout condition, drift abundance, and temperature were qualitatively consistent with bioenergetic models that predict fish growth should vary as a joint function of food and temperature. However, the inferred temperature optima for rainbow trout seemed to be significantly higher than predicted. Our results support a growing body of evidence that stream trout may be frequently food-limited in nature.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0824:VICORT>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Artificial fluctuations in streamflow caused by hydroelectric power dams can degrade fish habitat and reduce the abundance and diversity of riverine fish faunas. Increased minimum water releases and reduced fluctuations in discharge may mitigate these effects. In this study, we compared shoreline fish abundance and diversity before and after an enhanced flow regime was implemented on the Tallapoosa River (Alabama) downstream of a hydroelectric dam. Before the minimum-flow regime, only eight species of fish were collected 3 km downstream from the dam, and all were classified as macrohabitat generalists. After the minimum flow was initiated, species richness 3 km below the dam more than doubled, and over half of the species collected were classified as fluvial specialists. Fish community response to the enhanced flow was not as great at a site 37 km downstream from the dam, where species richness was similar between the two periods. However, more species classified as fluvial specialists were collected after the minimum flow regime than before enhanced flows at this site. Additionally, relative abundance of species classified as fluvial specialists increased from less than 40% of fish collected before enhanced flows to over 80% after minimum flows began. Our results suggest that the enhanced flow regime provided conditions supporting a relatively abundant and diverse fish assemblage more reflective of a riverine system.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0836:ROAWFA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The unimpounded lower Columbia River downstream from Bonneville Dam (LCR) supports the greatest abundance and density of white sturgeonAcipenser transmontanusreported in the species' range. The high productivity of the population resulted from growth that was as good as or better than reported for other populations, the highest mean relative weight reported for any white sturgeon population, and a relatively low median age (24 years) of first maturity for females (95% of females matured between 16 and 35 years of age). Estimated instantaneous natural mortality was 10%. During 1986–1990, the estimated instantaneous fishing mortality for age-12–17 fish averaged 36% in LCR fisheries. Over the same period, the average annual abundance estimate of LCR white sturgeon 54 cm fork length (FL) or longer was 895,500 fish, and the average density was 14.6 fish per ha. Population simulations, under the assumption of constant recruitment, predicted a maximum sustainable yield (MSY) of 3.0 kg/recruit at an 18% exploitation rate (of the 82–166-cm FL population). Reproductive potential was 93,400 eggs/recruit for an unexploited population and 4,800 eggs/recruit at the predicted MSY exploitation rate. The factors most responsible for the favorable production potential of the population were access to marine areas, abundant food resources, and consistently favorable hydrologic conditions during the spawning period.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0845:DAPPOW>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

White sturgeonsAcipenser transmontanuswere sampled in three lower Columbia River reservoirs from 1987 to 1991 to describe population dynamics, the ability of these stocks to sustain harvest, and differences among reservoir and unimpounded populations. Significant differences were observed among reservoirs in white sturgeon abundance, biomass, size composition, sex ratio, size of females at maturity, growth rate, condition factor, and rate of exploitation. No differences among reservoirs were detected in fecundity, natural mortality rate, or longevity, in part because of sampling difficulties. Recruitment rates and densities in reservoirs were inversely correlated with growth rate, condition factor, and size of females at maturity. Differences in population dynamics resulted in substantial differences in sustainable yields. Maximum yields per recruit were predicted at annual exploitation rates between 5 and 15%. Most characteristics of reservoir populations were less than or equal to optima reported for the unimpounded lower river; as a result, yield per recruit, reproductive potential per recruit, and the number of recruits were less in reservoirs than in the unimpounded river. Comparisons with pristine standing stocks suggest that the unimpounded river may approximate preimpoundment conditions for white sturgeon. We conclude that potential yield from impounded populations has been reduced by dam construction, which restricts populations to river segments that may not include conditions optimal for all life stages. Alternatives for enhancement of reservoir populations might include improved passage at dams, increased spring flow to improve spawning success, transplants from productive populations, hatchery supplementation, and more intensive harvest management.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0857:DITDAP>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Fall and winter movements of and habitat use by cutthroat troutOncorhynchus clarkiwere studied with radiotelemetry in low, mid, and high altitudes of a river system to evaluate the timing and extent of habitat shifts when fish moved from summer feeding areas to overwintering areas. The movements of 20 fish were monitored from August to November 1991, and 17 fish were monitored from October to December 1992. Cutthroat trout moved out of summer habitats in mid-September, and many made a two-stage shift in habitat use from summer to winter that was associated with anchor ice formation. When cutthroat trout were excluded from fall habitats by anchor ice, they moved to overwintering areas less likely to be influenced by frazil and anchor ice: deep pools with ice cover or areas where water temperatures were higher than the rest of the stream because of springs or upwelling warm groundwater. Cutthroat trout used deeper water and smaller diameter substrates in winter than in summer but used less cover during winter. Because of decreases in discharge and exclusion by anchor ice, cutthroat trout were forced into restricted suitable habitat, which resulted in large aggregations of fish. Cutthroat trout moved 0.0–7.6 km from summer to overwintering areas. They were stationary most of the time; when they did move, most movements exceeded 100 m. The number of movements made decreased from summer to winter.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0873:FAWMOA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Although the northern hog suckerHypentelium nigricansis widely distributed throughout the Mississippi and Ohio river basins and is both ecologically and recreationally important, much of its basic ecology is not known. We determined movement and habitat use for 25 fish in the Current River, Missouri, for 1 year using radio telemetry. Seasonal movements were recorded two or three times each week during daylight hours from January to November 1988. Diet movement and habitat use were recorded once each hour for 17 d in winter and 12 d in summer. Mean daily distance traveled was greater in summer (425 m) than in winter (276 m). Home range was greater in winter and spring (812 m) than in summer and fall (426 m). Habitat use changed seasonally from slower, deeper water and smaller substrates during winter to increasing use of taster, shallower water and larger substrates through warmer-water periods. In both seasons, fish had a consistent daily pattern, moving more during the day than at night. Diet patterns of use were distinct. In winter, fish used pool habitat with moderate flow during the day and riffle or edge habitat at night. In summer, fish used run habitat during the day and riffle or edge habitat at night. Patterns of habitat use indicated fish used one area of the river during the day to feed and another at night to rest. Fish remained in their home area during high-flow events but used flooded riparian areas where current velocities were lower. Fish moved up- or downstream short distances (mean = 497 m,N= 7) into spawning areas during late February and early March. This study emphasizes the importance of habitat diversity to accommodate this species' diel and seasonal preferences and the necessity of a connected floodplain for the fish to survive catastrophic events.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0886:POMAHU>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Age-0 bluefishPomatomus saltatrixwere widely distributed and seasonally abundant in shallow beach habitats of Narragansett Bay, Rhode Island. Based on length-frequency data that were polymodal in some years, these age-0 fish comprised spring- and summer-spawned cohorts. Cohort-specific measures of abundance, growth, total mortality and emigration, and size were determined for 1982–1992. In all years, spring-spawned fish dominated the catch from at least July to September. For this cohort, annual abundance varied by an order of magnitude, growth ranged from 0.9 to 2.1 mm/d, total mortality and emigration rates were between 0.2 and 2.8%/d, and mean length on October 1 ranged from 164 to 248 mm fork length. Spring-spawned fish were about twice as large as summer-spawned fish by October. Summer-spawned fish also occurred less frequently and in lower abundance. These findings confirm that Narragansett Bay is an important nursery for bluefish, and that the trend toward declining annual abundance measured in this bay is concordant with the reported decline of bluefish throughout the western Atlantic. Correlation analysis with data for only the spring-spawned cohort suggested density-dependent (i.e., compensatory) processes occurred; growth decreased monotonically but not linearly, relative to abundance, whereas combined mortality and emigration rates increased linearly. Measures of abundance were also a function of seine-net size; seines less than 25 m long were particularly ineffective for collecting age-0 bluefish. These relationships suggest that monitoring age-0 fish in estuaries may help predict future population size.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1995)124<0898:CVIASG>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor