摘要:

Changes in solar radiation, water temperature, periphyton accumulation, and allochthonous inputs and storage were measured after we removed patches of deciduous, second-growth riparian vegetation bordering two small streams in southeast Alaska that produce coho salmonOncorhynchus kisutch.Solar radiation and leaf litter input were measured at the water surface at random locations dispersed through six alternating closed- and open-canopy stream sections. Water temperature, periphyton, and stored organic samples were collected near the downstream end of each section. Solar radiation intensity was measured with digital daylight integrators and pyronometers, periphyton biomass and chlorophyllawere measured on red clay tile substrates, allochthonous input was measured with leaf litter baskets, and benthic organic matter was measured with a Hess sampler. Average intensity of solar radiation that reached the water surface of open-canopy sections was significantly higher than in closed-canopy sections of two streams measured during daylight hours in summer 1988 and of one stream measured day and night in summer 1989. Average daily water temperature was similar in the two canopy types in summer 1988, but was higher in open- than in closed-canopy sections in 1989. Accumulation of periphyton biomass was significantly higher in open- than in closed-canopy sections of the two streams studied in the summer of 1988 and of the one stream sampled in 1989. Accrual of periphyton biomass on tiles placed in the stream for 30-d colonization periods during the summer months of 1989 was also significantly higher in the open than closed sections. Accumulation of chlorophyllawas significantly higher in the open- than in closed-canopy sections of the two streams in 1988 but did not differ significantly between canopy types in 1989. Thirty-day accrual of chlorophyllawas greater in open- than in closed-canopy sections of the one stream studied in 1989. Allochthonous input to the streams decreased after canopy removal, but the amount of organic material stored in the substrate did not differ significantly between open- and closed-canopy sections. Weather was predominantly overcast and rainy in summer 1988 and mostly sunny with infrequent rain in 1989. We speculate that advective heat transfer and high stream discharge from frequent rains moderated the effect of canopy removal and increased solar radiation on water temperatures in open-canopy stream sections in 1988. In 1989, solar radiation was a significant factor in regulating water temperature, especially when streamflows were low. Using a model, we predicted that water temperatures would change little in a 160-m open-canopy reach of Eleven Creek during any weather condition when flows were high. With low flows, however, stream temperatures in open sections of Eleven Creek were predicted to exceed the optimum for growth of juvenile coho salmon in about 20 m during clear sunny weather and in about 50 m when cloudy and overcast.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0859:CISIWT>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We assessed changes in availability and consumption of invertebrates by juvenile coho salmonOncorhynchus kisutchin a small stream in southeast Alaska where patches of dense second-growth riparian vegetation bordering the stream had been removed. Benthic invertebrate populations were assessed during summer 1988 and 1989 with a Hess sampler. Aerial invertebrates were sampled during summer 1989 with wire-mesh sticky traps hung just above the water surface and with floating clear-plastic pan traps. Invertebrate drift was assessed during summer 1989 with nets placed at the downstream end of closed- and open-canopy stream sections. Diets of age-0 and age-1 coho salmon were sampled by flushing stomach contents of fish collected from closed- and open-canopy stream sections. Abundance and biomass of benthic invertebrates were larger in open- than in closed-canopy stream sections and were primarily dipterans, ephemeropterans, and plecopterans. More insects were caught on sticky traps in open than in closed sections on two of four dates sampled, and composition of the catch was primarily dipterans (74% in both closed- and open-canopy sections). Catch rates of invertebrates in the pan traps were significantly higher in closed than in open sections on 12 July and were greater in open than in closed sections on 11 August. No significant canopy effect was detected with regard to dry weight of insects captured in pan traps. Composition of the pan-trap catches was primarily dipterans in both closed and open sections (65% and 72%). Abundance of invertebrates in the drift was significantly higher in closed sections than in open sections on two of four dates sampled; dry weight of invertebrate drift did not differ significantly between canopy types. Dry weight of stomach contents of age-0 and age-1 coho salmon was greater for fish sampled in closed- than open-canopy sections on one of four dates sampled; no significant canopy effect was detected for the other three dates sampled. Aerial insects were more abundant in drift and in diets of age-0 and age-1 coho salmon in closed- than in open-canopy sections. Diet of age-0 coho salmon in both closed and open sections and diet of age-1 fish in closed sections overlapped significantly with composition of the drift. Diet of age-1 coho salmon in open sections, however, did not overlap significantly with drift, an indication of selectivity in feeding behavior. Based on higher abundance of aerial invertebrates above the water surface and increased standing crop of benthic invertebrates that we observed in open- versus closed-canopy sections of Eleven Creek, it appears that canopy removal has the potential to increase the carrying capacity of juvenile coho salmon in streams where populations are food limited.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0876:EOCROI>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We manipulated the canopy of second-growth red alderAlnus rubraand instream cover to assess the effects on abundance of juvenile salmonids in small streams of Prince of Wales Island, southeast Alaska, in 1988 and 1989. Sections of red alder canopy were removed to compare responses of salmonids to open- and closed-canopy sections. At the start of the study, all potential instream cover was removed from the study pools. Alder brush bundles were then placed in half the pools to test the response of juvenile salmonids to the addition of instream cover. Abundance of age-0 coho salmonOncorhynchus kisutchdecreased in both open- and closed-canopy sections during both summers, but abundance decreased at a higher rate in closed-canopy sections. More age-0 Dolly VardenSalvelinus malmawere found in open-canopy sections than in closed-canopy during both summers. Numbers of age-1 and older coho salmon and Dolly Varden were relatively constant during both summers, and there was no significant difference in abundance detected between open- and closed-canopy sections. Abundance of age-0 coho salmon decreased in pools with and without additional instream cover during both summers. Abundance of age-1 and older coho salmon and age-0 Dolly Varden did not differ significantly in pools with or without added cover during either summer. Abundance of age-1 and older Dolly Varden was higher in pools with added instream cover than in pools without cover during both summers. Age-0 coho salmon decreased in abundance throughout the summer in both years. Emigration was measured in 1989 and accounted for most of the decrease in abundance. Age-0 coho salmon emigrants were significantly smaller than age-0 coho salmon that remained in the stream.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0889:ROJSTR>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A North Carolina reef fish community was resurveyed with scuba gear to determine if changes occurred in community structure after 15 years of intense fishing. Generally, fishes important in the recreational and commercial fisheries were smaller, and large changes occurred in relative abundance and species composition. Indicative of a warming trend, total species composition of fishes had become more tropical, and a tropical sponge previously unrecorded at this latitude off the North Carolina coast became common. Two new (to the area) families and 29 new species of tropical fishes were recorded. Observations of 28 species of tropical reef fishes increased significantly. No new temperate species were observed, and the most abundant temperate species decreased by a factor of 22. Mean monthly bottom water temperatures in winter were 1–6°C warmer during the recent study. An increase in fish-cleaning symbiosis was especially noticeable.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0908:CIANCR>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We investigated mechanisms through which nonnative brook troutSalvelinus fontinaliscould negatively influence native Arctic graylingThymallus arcticus.We assessed occupied microhabitats, growth, and condition of Arctic grayling and brook trout in sympatric and allopatric groups in stream enclosures. Microhabitat use by both species was also measured in a natural assemblage. In stream enclosures and the natural assemblage, Arctic grayling and brook trout exhibited similar preferences for pools and runs, but they spatially segregated in microhabitats. Arctic grayling occupied faster focal point and mean column velocities closer to the surface than brook trout. Brook trout occupied slower focal point velocities in proximity to structural cover. Specific growth rates indicated that intraspecific competition operated more strongly than interspecific competition in regulating growth of both species in stream enclosures. In sympatry, Arctic grayling grew faster at a low density with a high density of brook trout. In contrast, Arctic grayling at high densities in the control and a sympatric treatment exhibited slow or negative growth. Similarly, brook trout grew faster in a low-density enclosure in sympatry with a high density of Arctic grayling. We found little evidence that nonnative brook trout negatively affected microhabitat use or growth of native Arctic grayling.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0921:CIBAGA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We used tethering to measure spatial and temporal patterns of relative risk of predation to age-0 rainbow troutOncorhynchus mykissover 2 years in five lakes that varied widely in the abundance of piscivorous rainbow trout. During the day, the most risky habitats were just above the thermocline near the substrate and in open water at the same depth. Risk was intermediate at the surface in the littoral zone and at the surface over the intersection of the thermocline and the lake bottom. The least risky habitat was at the surface in the open water. The intensity and spatial pattern of relative predation risk changed at dusk. The most risky habitat was still at the thermocline–lake bottom intersection, but it was more than twice as risky as during the day. At dusk, relative predation risk increased in the littoral zone and at the surface above the thermocline–lake bottom intersection. The open-water habitats, both at the surface and at the thermocline, had a low relative predation risk. Age-0 and older rainbow trout in the experimental populations segregated in their use of habitat, with the majority of age-0 trout in the littoral zone and the majority of older conspecifics in the pelagic zone. Survival rate of age-0 rainbow trout over the growing season was inversely correlated with instantaneous measures of relative predation risk but approached an asymptote at high relative predation risk, suggesting that the littoral zone provides a refuge that prevents the elimination of age-0 fish by piscivory.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0932:SATVIR>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We investigated distribution and dispersal patterns of subadult and adult Colorado squawfishPtychocheilus lucius(recently renamed the Colorado pikeminnow) throughout their range in the upper Colorado River. Annual, river-wide, capture–recapture data were used to document movements during a 5-year period (1991–1995). Average total length of Colorado squawfish progressively increased upstream: juveniles and subadults occurred almost exclusively in the lowermost 105 km of the 298-km study area, whereas most adults were concentrated in the uppermost 98 km. This was most pronounced early in the study and less so later due to the effect of two or three strong year-classes that dispersed through the system. Only 16% of subadult and adult fish initially captured and tagged in the upper reach were later located more than 10 km from the previous capture site; of those tagged in the lower reach, 58% were later located more than 10 km from the previous site. Most movements greater than 10 km were directed upstream, and many fish tagged in the lower reach moved to the upper reach; the smallest of these fish was between 421 and 449 mm in total length (TL) when it moved. No movement was detected from the upper reach to the lower. Distance moved was inversely related to fish size: displacement of fish shorter than 550 mm TL averaged 33.6 km; for those longer than 550 mm, average displacement was only 7.5 km. Movement of young adults may have been a response to changing food needs. Upstream movements placed fish into areas with greater availability of larger prey, and body condition of large adults during spring was significantly higher in the upper reach than in the lower reach. Water temperatures, however, were inversely related to adult distribution despite a preference for warmer water. We suggest that portions of the upper reach offer adults the best balance between food and water temperature.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0943:DPOSAA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Status of the Colorado River population of the endangered Colorado squawfishPtychocheilus lucius(recently renamed the Colorado pikeminnow) was investigated by (1) estimating adult numbers, (2) evaluating frequency of reproduction and recruitment, (3) identifying trends via changes in size structure over time, and (4) examining historical accounts for clues to former abundance. Adults and subadults were systematically captured from 278 km of river during 1991–1994. Larvae and age-0 fish were systematically sampled in two reaches during 1986–1994. Estimated number of adults in the upper 98 km averaged 253 individuals; estimated annual adult survival rate was 0.86. In the lower 181 km, estimates of subadults and adults combined averaged 344 individuals. A sizable pulse of subadults 300–400 mm long found in the lower reach in 1991 were from three year-classes, 1985–1987. By 1992, these were distributed throughout the river. Although catch rates of larger adults did not increase significantly in the upper reach during 1991–1994, catch rates of fish less than 550 mm long increased fivefold. Size-frequency analysis of lower-reach fish indicated the 1985–1987 cohorts were the largest produced since before 1977, and no similarly strong year-classes were produced subsequently. Estimated years of origin of these recruiting fish coincided with years of higher-than-average catch rates of larvae and age-0 fish in the upper reach and catch rates in subsequent years there were comparatively low. Very few individuals less than 450 mm long were found in the upper reach during the past 15 years, suggesting that recruitment there is from colonization from the lower reach. In contrast, significant numbers of fish less than 400 mm in total length occurred in the upper reach during the mid-1970s. Abundance appears much lower than suggested in historical accounts. Low adult numbers and sporadic pulses of recruitment may make this population vulnerable to extirpation. Though adult survival rate is probably fairly constant, recruitment is highly variable and may represent the most important demographic factor to population persistence.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0957:SATOTE>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Studies were conducted to determine the effects of water temperature on egg and larval production, larval survival, and juvenile growth of the endangered fountain darterEtheostoma fonticola.Adult fish were exposed to water temperatures of 14, 17, 20, 23 (control), 25, 27, and 29°C for 33 d. Egg production was significantly higher (P≤ 0.05) for fish held at 14, 17, 20, 23, and 25°C than for fish held at 27 and 29°C. Percent hatch was significantly higher (P≤ 0.05) at 17, 20, and 23°C than at 14, 25, 27, and 29°C. Larval production was significantly higher (P≤ 0.05) at 14, 17, 20, and 23°C than at 25, 27, and 29°C. Estimated low and high temperatures to produce 50% mortality of larvae (24–72 h old) over a 24-h period were 3.8 and 31.9°C, respectively. Low survival and substantial variation in growth of controls prevented a meaningful assessment of temperature effects on juvenile growth.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0971:EOTOEP>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The impacts of gravel mining on physical habitat, fine-sediment dynamics, biofilm, invertebrates, and fish were studied in three Ozark Plateaus gravel bed streams. Intense studies were performed upstream, on site, and downstream from one large mine on each stream. Invertebrates and fish were also sampled in disturbed and reference riffles at 10 small mines. Gravel mining significantly altered the geomorphology, fine-particle dynamics, turbidity, and biotic communities. Stream channel form was altered by increased bank-full widths, lengthened pools, and decreased riffles in affected reaches. Fine particulate organic matter transported from riffles to pools was decreased. Biofilm organic content was decreased on flats and increased on remaining riffles. Density and biomass of large invertebrates and density of small invertebrates were reduced at the small, more frequently mined sites. Total densities of fish in pools and game fish in pools and riffles were reduced by the large mines. Silt-sensitive species of fish were less numerous downstream from mines. Attempts to mitigate or restore streams impacted by gravel mining may be ineffective because the disturbance results from changes in physical structure of the streambed over distances of kilometers upstream and downstream of mining sites. Stream morphology was changed by lack of gravel bedload, not by how bedload was removed. Mining gravel from stream channels results in irreconcilable multiple-use conflicts.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1998)127<0979:IOGMOG>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor