摘要:

The vulnerability to UV-B radiation inAcanthocyclops robustuswas analyzed in the laboratory. The LD50for adult individuals, determined by mortality one day after UV-B exposure was 40 μ Wcm−2for 4 h exposure. A significant increase in the mortality ofA. robustusadults was observed four days after exposure to UV-B irradiation. As a consequence, the estimated lethal dose at four days post-exposure was 20% less than that estimated two days after the exposure. These results indicate that because there is significant latent mortality during the post-irradiation period, accurate assessment of mortality due to UV-B exposure can only be made four days after the irradiation. Copepodite IV life stage individuals were much more sensitive to UV-B exposure than were the adults.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663716

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In 1996 and 1998, standardized angling was conducted on four streams to determine the vulnerability of stock-length (≥ 180 mm) spotted bass (Micropterus puntulatus) to angling. Block nets were used to prevent movement of fish into or out of the reach. Two anglers fished the entire reach from the bank. After angling was completed, spotted bass were sampled using pulsed-DC backpack electrofishing equipment. A three-pass depletion method was used to estimate density. Population estimates varied from three to five stock-length spotted bass per 100 m of stream reach, and density varied from 21 to 63 spotted bass/ha. Mean angler catch per effort was 0.39 fish/h and potential harvest was 5.1 fish/ha. Percent of the spotted bass population that was captured by angling varied from 0% to 26%.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663717

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The Blue Hole Creek basin (1652 ha) is located in an area of Pennsylvania that is historically high in wet deposition of sulfates and nitrates. Five stations on Cole Run (chronically acidified) and one on Blue Hole Creek (episodically acidified) were sampled twice seasonally—once at base flow and once at high flow. Total iron, aluminum, and sulfate trended toward a direct relationship with discharge, while pH and alkalinity exhibited an inverse relationship. Stations with higher pH values were linked with the Mauch Chunk geologic formation and Fluvaquents soil series, while those with lower pH were linked with the Pottsville geologic formation and the Brinkerton, Cookport, and Rayne-Gilpin soil series. Fewer macroinvertebrates were collected from the episodically acidified station than at any of the chronically acidified stations on 71% of the sample dates. Although the number of taxa was similar between stations (n=16-23), more taxa were unique to Cole Run than to Blue Hole Creek. Shredder and collector functional groups dominated in Cole Run, while in Blue Hole Creek functional groups were more balanced, or dominated by predators or collectors depending on season. No clear patterns were discerned for season or flow. High flows, however, tended to produce higher diversity values at stations usually dominated by a single taxon. Despite chronic acidification, stations on Cole Run showed diversity and equitability values similar to, and occasionally exceeding, those of the episodically acidified stream.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663718

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We developed a microhabitat sampling methodology for investigating fish habitat use by radio telemetry. The technique is based on the concept of an area of probable occurrence (APO; a circular confidence interval around an estimated fish location) with measurements of depth, velocity, substrate, and cover features to describe the habitat in the vicinity of a fish's location. We conducted a test of precision and observer agreement of data obtained by this technique and found that the statistical precision of data varied among habitat variables and was low for features that were visually estimated. However, when data were interpreted within the context of several biologically relevant research questions, observer agreement was high indicating that the data led to consistent conclusions regarding microhabitat features within an APO.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663719

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The effects of water current on phytobenthos colonization in different seasons of the year were studied in a high-nutrient pampean stream of Buenos Aires province (Argentina). The accumulation rates of the community in places with different flows were estimated with artificial substrata which were removed in three-five day intervals during aproximately one month in each of the four seasons of the year. Biomass was measured as chlorophyll-a.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663720

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The upper Cahaba River in Alabama has experienced extensive urban development in its watershed in recent years. To assess the effects that these developments have had on the ichthyofauna, we compared data from samples made at 12 stations by other researchers prior to 1984 to data from samples collected by us at the same sites between 1995–97. Historical collections produced a total of 44 species, whereas recent samples produced 42. Two species, the blue shiner (Cyprinella caerulea) and the Alabama shad (Alosa alabamae), have been extirpated from this system. Relative abundances of the various taxa in recent samples correlated poorly with those of historical samples, indicating that the compositions of the ichthyological communities have changed. Disturbance-tolerant cyprinids (minnows) have generally increased in percent relative abundance (PRA) in recent collections, whereas the disturbance-sensitive cyprinids have generally decreased. The PRA of percids (darters) has decreased in recent collections, especially the disturbance-sensitive species such as the coal darter (Percina brevicauda) and the greenbreast darter (Etheostoma jordani). The ichthyofaunal diversity, as measured by several indices, has decreased in recent samples. These changes in the fish populations have occurred concurrently with extensive urbanization and resultant degradation of water and habitat that has taken place in the watershed over the last 20 years.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663721

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Dynamics and structure of a benthic macroinvertebrate community were studied during two years after a severe drought of a lake. Three families were dominant over the two-year study: Corixidae (31.90 %), Chironomidae (23.05 %) and Planorbidae (8.01 %). Temporal fluctuations were interpreted in relation to environmental conditions and life histories of macroinvertebrates.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663722

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Biomass, production, and yield of the pelagic fish communities were estimated in Laguna Grande of San Pedro (eutrophic), Laguna Chica of San Pedro (mesotrophic) and Lake Icalma (oligotrophic), all belonging to the Andean basin of the Biobío river (36°45′-39°S), Chile. Fish biomass showed differences that were related to the trophic state of the lakes. The highest biomasses were in the eutrophic lakes, with mean values of 563 kg ha−1in Laguna Grande of San Pedro and 591 kg ha−1in Laguna Chica of San Pedro. The lowest biomass was in Lake Icalma with a mean of 164 kg ha−1. The estimated annual yields were 170 kg ha−1in Laguna Grande of San Pedro, 157 kg ha−1in Laguna Chica of San Pedro, and 32 kg ha−1in Lake Icalma. In Laguna Grande of San Pedro, the highest percentage of fish yield was the non-salmonid species, including Cyprinids (Cyprinus carpioandCarassius carassius) with 87.2%, and only 12.8% wasOncorhynchus mykiss, the only salmonid species in this lake. The same pattern was observed in Laguna Chica of San Pedro, with 78.6% forOdontesthes bonariensisand 21.4% forO. mykiss. In Lake Icalma the pattern was opposite, with a 90.2% for the salmonid species (O. mykissandSalmo trutta) and only 9.8% forPercichthys trucha.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663723

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The effects of freshwater sponge (Porifera) overgrowth on the fitness of adult zebra mussels (Dreissena polymorpha) were examined in East Chicago and Michigan City, Indiana harbors in southern Lake Michigan. There was significant reduction in glycogen content of sponge-covered zebra mussel soft tissue wet weight (mean=2.6%) when compared to the non sponge-covered population (mean=3.9%). Similarly, the soft tissue wet weight of sponge-covered zebra mussels (15 to 25 mm size class) was lower when compared to non-covered mussels. A comparison of the live:dead ratios of zebra mussels in both populations showed overgrowth by sponges had a significant lethal effect. These data suggest that the epibiont growth of freshwater sponges on adult zebra mussel shells negatively impacts the growth and survivability of zebra mussels.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663724

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Vegetative riparian buffer strips are typically used to curb stream degradation due to cattle grazing, but intensive rotational grazing has shown promise as an alternative best management practice. We compared aquatic macroinvertebrate assemblages among stream segments within continuously grazed pastures, intensive rotationally grazed pastures, undisturbed grassy vegetative buffer strips, and undisturbed woody vegetative buffer strips. We collected macroinvertebrate and stream sedimentation data from four streams in each land use category in two consecutive years. In an attempt to account for inherent watershed variability among streams, we represented watershed condition with a sample collected upstream of each treatment reach. Watershed condition tended to have greater influence on macroinvertebrate measures than local riparian land use. However, local riparian land use influences were apparent if watershed condition was statistically accounted for with analysis of covariance. Stream reaches with intensive rotational grazing tended to have macroinvertebrate assemblage characteristics intermediate of the buffer and continuously grazed reaches. Although we detected some differences in macroinvertebrate assemblages that apparently reflected very local land use, our results suggest the macroinvertebrates were mostly responding to large-scale watershed influences.

ISSN:0270-5060    

DOI:10.1080/02705060.2000.9663725

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor