摘要:

We examined relationships between the biomass of trout (species of Salvelinus and Salmo) and physical and biological habitat variables in streams to identify habitat factors that might limit trout biomass. Thirty sites were chosen to span a wide array of habitat types. At each site we measured a large number of habitat variables representing instream cover, substrate, stream morphology and velocity, stream temperature and food availability. Two habitat quality index models developed by Binns and Eiserman for Wyoming streams accounted for only 6.7 and 9.2% of the variation in trout biomass at Ontario stream sites. Different factors must limit trout biomass in Wyoming streams than in Ontario streams. Regression and discriminant function analyses indicated that trout biomass in southern Ontario is correlated with microcommunity biomass (measured as ATP of the suspended solids, and representing bacteria, fungi, and algae), percent pool area, mean maximum summer temperature, biomass of small benthic invertebrates, presence of piscivorous fish, and a variable representing pools and overhead cover. Microcommunity biomass was the most important habitat variable in these analyses and it was significantly correlated with basin yield. We hypothesize that microcommunity biomass is a surrogate measure of localized groundwater inflow, which, in turn, has a beneficial effect on the microhabitat of trout eggs and underyearlings.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<503:TBAHRI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The feeding habits of a population of stunted lake trout Salvelinus namaycush in Lake Louisa, Algonquin Park, Ontario, suggest that these fish are facultative planktivores in summer. Although other prey such as cyprinids and mayfly larvae were eaten, these fish fed mainly on zooplankton. They selected large cladocerans (99% of zooplankters eaten were Daphnia sp. longer than 0.9 mm), even though similar-sized copepods sometimes were more abundant in the lake. Electivities were similar for each depth stratum examined. We suggest the lake trout used all parts of the water column while foraging, and were not restricted to deep water as previously believed. However, periodic foraging excursions into the warmer summer epilimnion, low abundance of large prey, and gastric inefficiency may all contribute to the stunting of lake trout in this lake.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<515:PBSLTI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We developed a model predicting the filtering efficiency of different sizes of filter-feeding gizzard shad Dorosoma cepedianum. The model is based on the cumulative frequencies of interraker distances of the gill rakers and was corroborated by feeding trials in which gizzard shad ingested different sizes of suspended plastic microspheres and plankton. The proportion of particles removed by fish increased as a function of particle size, leveling off when particle diameters exceeded 35 μm for small fish (7.1–11.1 cm standard length, SL) and 55 μm for large fish (13.6–16.3 cm SL). According to selectivity index values computed from the filtering efficiency model, gizzard shad of 5, 15, and 25 cm SL would selectively feed on particles larger than 19, 40, and 63 μm, respectively. This change in selective particle ingestion may explain why phytoplankton becomes less important in the diet of gizzard shad and why this clupeid shifts its feeding niche as it increases in length.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<522:EOFSOT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The fall downstream migrations of juvenile American shad Alosa sapidissima and blueback herring Alosa aestivalis were monitored for 3 years in the Connecticut River at Holyoke Dam, Massachusetts. Decreasing water temperature—not increasing river flow—determined the time migration began and ended for both species. The migration of blueback herring began in September as water temperature declined to 21°C, peaked at 15–14°C, and ended in late October or early November at 10°C. The American shad migration began at 19°C, peaked at 14–9°C, and ended at 10–8°C. Most movement peaks were centered on quarter-moon periods; seven were centered on a new moon and none was centered on a full moon. The diel pattern of migration varied among the 3 years. In general, however, blueback herring were active throughout the 24-h period (peak activity at 1800 hours), and American shad moved in the afternoon and evening (peak activity between 1800 and 2200 hours). The migration of juvenile American shad may be mediated by decreasing temperature such that, as a threshold of 19°C is reached in the fall, the behavioral tendency to maintain position against the current in low light or at night is curtailed and the juveniles drift downstream. Sex ratios of American shad were not 1:1; females dominated in 1980 and males in 1981 and 1982. Sex ratios of blueback herring were 1:1 in 1980 and 1981, but males significantly outnumbered females in 1982. The mean total fish lengths increased significantly during the course of the migration for American shad in 1982 and for blueback herring in 1981.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<529:BLASRO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The distribution of redds of chinook salmon Oncorhynchus tshawytscha was evaluated in October-November 1978–1983 on Vernita Bar, about 6.5 km downstream from Priest Rapids Dam on the Columbia River. Minimum flows of 1,020 m3/s (license minimum set by the Federal Energy Regulatory Commission) and 1,416 m3/s were maintained in six alternating years, but flows each day fluctuated widely above the minima because of power production; part of the spawning area was exposed for several hours on most days. We detected no effect of minimum flow regime on redd size. Chinook salmon spawned at depths as great as 7 m below the water surface as measured at a discharge of 1,020 m 3/s. The highest redds occurred near the water's edge at the 1,982-m3/s flow elevation. Vertical range of spawning use was 8.5 m. Water velocities at 23 cm above the substrate (facing velocity) on the area used for spawning varied greatly with river discharge, but usually exceeded 0.67 m/s. Chinook salmon females completed redds in areas that were not covered by water for up to 8 h/d, and on other areas that had velocities near 2 m/s for part of each day. Chinook salmon spawned at Vernita Bar in areas with high fractions of cobble and low percentages of fines. They began spawning in early October below the 1,020-m3/s flow elevation and increasingly used the area between the 1,020- and 1,982-m3/s flow elevations until spawning ended about the third week of November. The percentage of redds above the 1,020-m3/s flow elevation correlated strongly with mean daily discharge during late October and early November over 7 years. We found no evidence that the minimum daily flow affected redd distribution in any way. Egg retention in ovaries of postspawning females, one measure of spawning success, was minimal in all years, as was the proportion of excavated redds that contained no embryos. Daily flow fluctuations from minima to 3,400–4,250 m3/s did not prevent females from completing redds. We concluded that minimum flows of 1,020 m3/s for up to 8 h/d do not determine availability of spawning habitat, and that use of spawning areas above the 1,020-m3/s flow elevation could be reduced by managing the river discharge with storage manipulation upstream to provide lower mean daily flows, thus easing minimum flow restrictions during posthatch incubation and emergence.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<537:EORFOT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The growth rate of the silver hake Merluccius bilinearis in the northern Georges Bank-Gulf of Maine stock appears to be highly density-dependent after fish reach the size at which they become piscivorous. The correlation between mean weight of age-2 through -5 fish and three estimates of relative stock density (catch per unit effort CPUE from commercial vessels, and virtual population analysis VPA of biomass and abundance) for the period 1962–1979 was analyzed by regression and Spearman rank correlation analyses. Mean weight at age was significantly and inversely correlated with estimates of stock density for all ages, although correlation coefficients were markedly lower for age-2 fish than for older age-groups. The lower correlation for age-2 fish may be due to reduced feeding competition with the adult stock, because silver hakes feed almost entirely upon invertebrates until becoming piscivorous after reaching 20–30-cm fork lengths between ages 1 and 2. Mean weight of age-2 fish was not correlated with year-class abundance, suggesting that growth rate may be density-independent for pre-adult life stages of this stock. Correlation was highest for age-3 fish; 84 and 75% of the variation in mean weight was explained by variation in CPUE and VPA biomass estimates, respectively. Growth of older fish seemed to be density-dependent only during periods when stock density was high. Mean weight at age was not correlated with CPUE for age-3 fish when data from only periods of low stock density were considered, but was significantly and inversely correlated when data from periods of high stock density were considered. The frequency with which density-independent growth has been identified in natural populations is probably due to the confounding effect that environmental variability and biological interactions have upon growth, and the probable reduction in intraspecific competitive pressure associated with exploited fish stocks maintained at low levels of density.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<548:DGOSH>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A 30-month study of the comparative dynamics of the fish populations inhabiting Kelsey Creek, located in the City of Bellevue, Washington, and a nearby pristine control stream suggest that urban development has resulted in a restructuring of the fish community. Environmental perturbations, including habitat alteration, increased nutrient loading, and degradation of the intragravel environment appeared to have a greater impact on coho salmon Oncorhynchus kisutch and nonsalmonid fish species than on cutthroat trout Salmo clarki. Although the total biomass (g/m2) of fish in each stream was similar, its composition differed markedly. Ages 0 and I cutthroat trout were the majority of the fish community inhabiting Kelsey Creek, whereas the control stream supported a diverse assemblage of salmonids of various ages and numerous nonsalmonids. The rapid growth and greater biomass of salmonids in Kelsey Creek (a 2-year mean of 3.51 g/m2versus 2.03 g/m2in the control stream) resulted in a total annual net production of these species of 1.6 to 3.3 times that of the control stream (a 2-year mean of 7.6 g/m2versus 3.5 g/m2in the control stream). Marking and outmigrant studies indicated that environmental disruptions in the urban stream do not result in the displacement of the salmonid inhabitants.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<555:EOUDOF>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The demographic and genetic population structure of plains killifish Fundulus zebrinus is presented for fish collected from tributaries of the Kansas and Arkansas river basins in Kansas. Electrophoretic analysis revealed heterozygote deficiencies in fish populations from both basins. These deficiencies are attributed, in part, to a temporal Wahlund effect caused by sampling across length classes of fish of differing genotype frequencies. Individual heterozygosity estimates were not associated with length, sex, or wet weights of fish. However, the proportion of heterozygous genotypes within a river was significantly correlated with the proportion of juveniles collected from the river. This association suggests a relationship between genetic heterozygosity and population fitness in this species. Total mean genic diversity and genetic differentiation among river populations was greater in the Arkansas basin. However, relative genic differentiation among sites within rivers accounted for more of the total genic differentiation in Kansas than in Arkansas basin populations. It is hypothesized that these results may be attributed to decreased gene flow and reduced population densities in the Kansas basin, both effects of relatively greater environmental alteration in this basin than in the Arkansas basin.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<568:PDAGSO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Animals usually encapsulate artificial implants placed in the abdominal cavity, but some fish species are unique in exhibiting transintestinal expulsion of the implant. Gross and histological examination were used to study the mechanisms of expulsion of artificial implants from channel catfish Ictalurus punctatus. Silicone-rubber- or paraffin-coated polystyrene transmitter capsules (0.5% or 2.0% of the fish's body weight) were surgically implanted into the peritoneal cavity of 74 adult channel catfish. Within 23 d, 39 transmitters had been expelled: 14 through the intestine, 24 through the incision, and one through a lesion in the ventral body wall. Two fish died, but 33 fish retained transmitters for the duration of the experiments (14–23 d); at necropsy, four transmitters were free in the abdominal cavity, 11 had limited fibrous proliferation, 14 were fully encapsulated by fibrous connective tissue, and four were partly or fully in the intestinal lumen. A fibrous connective tissue capsule was present in all but three fish that expelled their transmitters. Contraction of myofibroblasts, a prominent cell type in the fibrous capsule tissue, provided the force for expulsion. Expulsion occurred through the incision only when the transmitter was encapsulated over the incision. Anal exits occurred when the transmitter was encapsulated on the intestine and focal inflammation weakened the intestinal tissue layers and allowed the transmitter to pass into the intestine. Tissue reactions and number of incision exits were significantly greater with transmitters 2.0% of body weight than with transmitters 0.5% of body weight. Incision exits were more frequent in gravid females than in males or spent females. The kind of transmitter coating had no significant effect on expulsion.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<577:PAMFEO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The effects of three concentrations of copper (0.034, 0.057, and 1.30 mg/L) on the behavior of social groups of bluegills Lepomis macrochirus were examined. Social hierarchy formation was similar in all test groups. Ten behaviors, including respiratory disruptions and changes in comfort movements and aggression, were monitored. At the group level, there was a significant positive dose-response relationship demonstrated for coughs, yawns, fin flicks, nips and threats. The most subordinate and most dominant individuals of the hierarchy were affected more than the other fish. Subordinate fish had higher cough, yawn, and fin-flick frequencies during treatment than all other fish in the population; the dominant fish had the next highest frequencies. The aggressiveness of the dominant fish in each tank increased after copper exposure. The observation of significant behavioral changes at copper concentrations as low as 0.034 mg/L demonstrated that behavior can be a sensitive indicator of copper stress.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1986)115<590:BCISGO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor