摘要:

We used an individual-based model to examine possible explanations for the dominance of rainbow troutOncorhynchus mykissover brook troutSalvelinus fontinalisin southern Appalachian streams. Model simulations were used to quantify the effects on interspecific competition of (1) competitive advantage for feeding sites by rainbow trout, (2) latitudinal differences in stream temperatures, flows, and daylight, (3) year-class failures, (4) lower fecundity of brook trout, and (5) reductions in spawning habitat. The model tracks the daily spawning, growth, and survival of individuals of both species throughout their lifetime in a series of connected stream habitat units (pools, runs, or riffles). Average densities of each species based on 100-year simulations were compared for several levels of each of the five factors and for sympatric and allopatric conditions. Based on model results and empirical information, we conclude that more frequent year-class failures and the lower fecundity of brook trout are both possible and likely explanations for rainbow trout dominance, that warmer temperatures due to latitude and limited spawning habitat are possible but unlikely explanations, and that competitive advantage for feeding sites by rainbow trout is an unlikely explanation. Additional field work should focus on comparative studies of the reproductive success and the early life stage mortalities of brook and rainbow trout among Appalachian streams with varying rainbow trout dominance.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0001:FACDOR>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Surviving pure-strain populations of westslope cutthroat troutOncorhynchus clarki lewisiin headwater lakes of Glacier National Park could play an important role in the managed recovery of regional cutthroat trout fisheries. However, uncertainty exists about whether native trout could have naturally invaded several park lakes where they now occur. This study used paleolimnological techniques to address the question of whether the population of native trout in Avalanche Lake is indigenous or became established through an undocumented introduction. The validity of using fossil diapause eggs (ephippia) of the fish-sensitive cladoceransDaphniaspp. as indicators for the historical presence of zooplanktivorous fish was tested with a survey of live zooplankton and corresponding surface-sediment fossil assemblages in eight Glacier Park lakes with and without trout. Analysis of a sediment core from Avalanche Lake dated by lead radioisotopes, historical wildfires, and a flood allowed reconstruction of zooplankton dynamics from about 1700 A.D. to the present. FossilDaphniaephippia were rare or absent in Avalanche Lake sediments deposited before 1910, suggesting intense zooplanktivory due to sustained presence of an indigenous population of native cutthroat trout. Fossil evidence for largerDaphniapopulations in the 1930s and early 1940s revealed a temporary disturbance of the lake's normal food web interactions during which zooplanktivory was significantly reduced. This disturbance may have resulted from a collapse of the native trout population caused indirectly by failed attempts between 1915 and 1943 to stock Avalanche Lake with Yellowstone cutthroat troutO. clarki bouvieri.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0021:FZATHS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We sampled fish assemblages and quantified production dynamics of brook troutSalvelinus fontinalis, brown troutSalmo trutta, and rainbow troutOncorhynchus mykissin 13 southeastern Minnesota streams during 1988–1990 to examine the influence of water quality on fish populations in fertile trout streams. Fish assemblages in 15 stream reaches were abundant, but low in diversity; 13 species were collected. Parameter means (ranges) over the reaches were species richness, 4.1 (1–8); density, 29,490 (1,247–110,602) fish/ha; and biomass, 253.5 (49.6–568.6) kg/ha. Means (ranges) for salmonids were annual mean density, 2,279 (343–8,096) fish/ha; annual mean biomass, 162.0 (32.5–355.5) kg/ha; and annual production, 155.6 (36.7–279.6) kg/ha. Salmonid production and mean biomass were greater during the spring-fall interval than during fall-spring; young cohorts (ages 0–1) contributed the greatest proportion to population biomass and production. Salmonid annual production-to-mean-biomass ratio (P/B) averaged 1.06 (0.64–1.42), and means were significantly different among species (1.03 for brown trout, 1.54 for brook trout, and 1.92 for rainbow trout). A significant linear model was developed that describes P/B as an inverse function of population age structure and may be used to improve accuracy in approximations of annual production from mean biomass. Fish density, biomass, or production were not correlated with eight water quality variables describing ionic and nutrient content in these streams, but when data from other United States streams with a wide range in alkalinity were incorporated, salmonid production was strongly, positively correlated with alkalinity. The wide range in fish population and production statistics and their lack of correlation with water quality suggest that no uniform fish carrying capacity exists among these streams and that factors other than water fertility limit fish density, biomass, and productivity at this spatial scale, but the overall maximum production rate in the region may be governed by water quality.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0035:TPDAWQ>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Regional habitat and fisheries management planning requires estimates of the capacity of watersheds to produce salmonids. To predict the average abundance of smolts of coho salmonOncorhynchus kisutchproduced by streams and rivers, we related estimates of smolt abundance to habitat features derived from maps and discharge records. We assembled a database of 474 annual estimates of smolt abundance from 86 streams in western North America for this analysis. We found that only stream length and to a lesser extent latitude were useful in predicting mean smolt abundance, The frequency distribution of annual estimates of smolt abundance from individual streams tended towards a normal rather than the more usual lognormal distribution; the median coefficient of variation in abundance was 37%. Our results are consistent with the view that, on average, smolt abundance is limited by spatial habitat, but that there is significant annual variation in abundance probably due to variation in habitat quality caused by climate, flow, or other factors. We conclude that forecasting smolt yield from stream length and latitude is feasible at the watershed or regional level, but that the precision of a prediction for a single stream is poor. A more detailed approach will be required for local forecasting.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0049:EROCSS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We developed habitat suitability criteria (HSC) for mean column velocity and depth from a foraging model (foraging-model HSC) that incorporated the energetic costs and benefits of a foraging location for drift-feeding brook troutSalvelinus fontinalisin Hunt Creek, Michigan. We compared these criteria to HSC developed from frequency-of-use data (use HSC) collected in Hunt Creek. Foraging-model HSC predicted that a single mean column velocity was optimal and depended on fish size, whereas a range of optimal mean column velocities was predicted from frequency-of-use data. The optimal velocities predicted from foraging-model HSC for yearling and older brook trout (range 32–49 cm·s−1) were greater than the highest optimal velocity (27 cm·s−1) predicted by use HSC. The optimal-velocity values predicted from foraging-model HSC for age-0 fish (23 and 29 cm·s−1for 5- and 7.5-cm fish, respectively) were within the range of optimal velocities (6–30 cm·s−1) predicted from use HSC. The predicted range of usable velocities was narrower for foraging-model HSC than for use HSC, regardless of fish size. Foraging-model HSC values for depth were a function of current velocity and fish size and were similar to use HSC. Use HSC suitability scores for an independent set of habitat use observations in Hunt Creek were significantly higher than foraging-model HSC for age-0 fish but not for yearling and older fish. This may indicate that use HSC are too general and do not represent the actual suitability of foraging microhabitats in Hunt Creek. Yearling and older brook trout used microhabitats with higher mean column velocities and greater depths than age-0 fish.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0065:DAEOAH>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Young-of-the-year (age-0) brook troutSalvelinus fontinalisthat were spawned in a lake were observed migrating into and inhabiting small (<2-m-wide) inlet streams. We estimated that up to 81% of the entire age-0 population in the lake system inhabited the streams by midsummer. Some age-0 fish overwintered in the streams and remained there during their second summer. Such behavior suggested fitness advantages were gained by stream residence. The inhabited streams had accessible, cold, and stable habitats that existed because the streams occurred in forested catchments where groundwater dominated base flows. This identification of these small streams as habitat for young brook trout and the importance of catchment hydrology for sustaining these habitats indicated a need to review habitat protection guidelines for lake-dwelling populations.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0077:UOSSBY>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Factors affecting abundance, growth, and survival of age-0 gizzard shadDorosoma cepedianumwere examined in Pomme de Terre and Stockton lakes, Missouri, during 1987–1991. Otolith ages were used to assign larvae (≤25 mm total length, TL) and juveniles (>25 mm TL) to weekly cohorts so that cohort-specific estimates of abundance, growth, and survival could be made. The distribution of initial abundances of larvae among weekly cohorts was influenced by water temperature and reservoir water level but not by characteristics of adult females (abundance, size, condition, fecundity). Intense periods of spawning activity during rising water levels resulted in high peaks in larval abundance and relatively few large weekly cohorts (e.g., 1990). In the absence of water level rises, peaks in larval abundance were much lower and abundances of larvae were more evenly distributed among several cohorts (e.g., 1988). Spring warming also affected spawning; early cohorts in warm springs (1987 and 1991) were relatively more abundant than those during cool springs (1989 and 1990). The initial distribution of larvae among weekly cohorts influenced subsequent interactions between the larvae and their environment. Growth of larvae was positively affected by water temperature and, to a lesser degree, food abundance. Early cohorts grew slower because of lower water temperatures, and they suffered higher mortality than did late cohorts. Survival was also density dependent; weekly cohorts with high initial densities experienced lower survival than cohorts with small initial densities. High survival of larvae occurred in 1988 when densities of larvae were low and evenly distributed among weekly cohorts and food abundance was high. Growth and instantaneous mortality of juveniles were not closely tied to any single variable. Growth was positively related to food abundance and negatively related to gizzard shad density. Mortality was not significantly related to any measured variable. Overall, findings indicate that cohort dynamics of age-0 gizzard shad are initially driven by climatic factors and later by a combination of climatic and biotic factors.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0084:FAAGAS>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Relationships among age-0 gizzard shadDorosoma cepedianumand their predators were examined over 5 years (1987–1991) in Pomme de Terre and Stockton lakes, Missouri. to determine the influence of gizzard shad abundance and size on diets, diet overlap, and growth of predators. Within years, temporal changes in age-0 gizzard shad size affected predator diets and diet overlap of predators more than abundance. Age-0 gizzard shad were not important as prey until they grew larger than 25 mm total length, even though larval densities were much higher. They were the most common prey for most predators during June through October and diet overlap among predators was usually highest during that period. Lengths of age-0 gizzard shad ingested by predators resembled those available in the reservoirs throughout much of the season except in early summer, when predators ingested larger-than-average individuals, and in the fall, when smaller predators ingested smaller-than-average individuals. Among years, variations in summer production (kg/ha) and mean weight (g) of age-0 gizzard shad were significantly correlated with their importance in most predator diets and with diet overlap among predator species in Stockton Lake but not in Pomme de Terre Lake, possibly because age-0 gizzard shad were always abundant in Pomme de Terre Lake and annual variation in gizzard shad variables was less in Pomme de Terre than in Stockton Lake. One or both of these gizzard shad variables were usually significant in regression models explaining variation in growth increments of predators. When significant, production of age-0 gizzard shad was positively related to the species' importance in predator diets, to diet overlap among predators, and to predator growth, but mean weight of age-0 gizzard shad was negatively related to those variables. Because mean weight and mean density of age-0 gizzard shad were strongly negatively correlated, predators may have been responding more strongly to prey density than to prey size. Size of age-0 gizzard shad appeared to most strongly influence growth of smaller predators, whereas age-0 gizzard shad production most strongly influenced growth of larger predators. I conclude that changes in age-0 gizzard shad abundance and size can significantly influence predator diets, diet overlap among predators, and predator growth.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0101:IOAASO>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We documented the age and growth of alewivesAlosa pseudoharenqusin Lake Ontario during 1978–1992 and determined if growth was affected by intraspecific competition for epilimnetic zooplankton, lake temperature, or demand of salmonine piscivores for prey. Ages of juvenile alewives were determined from scales during 1978–1983, and ages of juvenile and adult alewives were determined from otoliths during 1984–1992. Indices of abundance for alewives were calculated from spring bottom trawl catches in 1978–1992; zooplankton density and epilimnetic temperature were monitored at two stations during 1981–1991; and salmonine demand each year during 1978–1992 was calculated with a simulation model. Although we encountered 11-year-old alewives, few fish lived longer than 7 years, and most fish in the population were younger than 6 years. Mean sizes at ages 1, 2, and 3 in spring averaged 93 mm (5.1g), 133 mm (17 g), and 149 mm (22 g), but from age 3 to age 8, mean size increased by only 5–7 mm and 2–3 g per year. Female alewives lived longer than male alewives and were always longer than male alewives at age 4 and older. Epilimnetic temperatures were suitable for rapid growth of juvenile alewives each year. Lake temperature had the potential to affect growth of adults but adult growth was not correlated with temperature suitability indices perhaps because temperature regimes differed among lake regions and alewives were mobile, Growth of alewives was not correlated with salmonine demand for prey. Competition for zooplankton among the two youngest alewife cohorts affected growth of age-1 alewives. Zooplankton density declined sharply in 1986, and should it decline again, growth of age-1 alewives will slow, unless numbers. of age-0 alewives fall. Whether growth of age-1 fish declines or numbers of age-0 fish fall, the result of another decline in zooplankton density will be a reduction in the production of alewives needed to support piscivores.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0112:AAGOAI>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Natural hybridization between black crappiePomoxis nigromaculatusand white crappieP. annularisrecently has been documented in reservoirs of the southeastern United States, including Weiss Reservoir in Alabama. In this study, we examined hybrid zone dynamics of crappies in Weiss Reservoir using allozymes and restriction fragment length polymorphisms of the cytochrome-bregion in mitochondrial DNA (mtDNA) to (1) determine the maternal parent of F1hybrid crappies in this reservoir and (2) compare levels of mtDNA gene flow in this hybrid zone with those from other hybrid zones. We found that hybridization was reciprocal between the two crappie species. In addition, the percentage of F1hybrids with white crappie as their maternal parent was not significantly different (P> 0.10) from the expected value based on abundances of each parental species in Weiss Reservoir. Past studies of mtDNA gene flow in hybrid zones found that hybridization was unidirectional. Thus, results of this study suggest that current hypotheses on mtDNA gene flow in hybrid zones are not universally correct or that the crappie hybrid zone in Weiss Reservoir is an atypical outcome of habitat change (impoundment of the Coosa River).

ISSN:0002-8487    

DOI:10.1577/1548-8659(1997)126<0127:SHBBCA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor