摘要:

Standard netting surveys have been ongoing since 1956 in Lake Sakakawea, a Missouri River main stem reservoir, and have identified 58 different species of fish. Regression analyses were performed for the total catch rate (CPUE), total weight catch rate, and the CPUE for 20 common fish species to determine trends in fish abundance over time. Significant (P<0.05) positive trends in abundance were found for walleye (Stizostedion vitreum), white bass (Morone chrysops), spottail shiner (Notropis hudsonius), and johnny darter (Etheostoma nigrum). Significant negative trends in abundance were found for crappie (Pomoxis annularisandP. nigromaculatus), yellow perch (Perca flavescens), common carp (Cyprinus carpio), and goldeye (Hiodon alosoides).

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663698

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The design of the subsampler described here is suited to both macroinvertebrate and plankton samples containing animals between 250 and 2000 μm in size. The subsampler is cheap to construct and is simple and fast to operate. It allows accurate enumeration of rare taxa and rapid subsampling to efficiently count abundant taxa.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663699

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Six Rio Grande basin cyprinid taxa compose a reproductive guild that spawns during increases in stream flow and broadcasts semibuoyant (drifting) eggs in the current. Spawning by guild members is naturally initiated by elevated flows during spring snow-melt or summer rainstorms, but reservoir releases now also result in spawning. Location or development of a material that mimics the physical properties of semibuoyant eggs of guild members would enable quantification of the displacement of drifting eggs and assessment of the additive impacts of stream flow, instream barriers, and habitat modifications on populations of these fishes. To initiate this search, the size and terminal velocity of guild members' eggs was determined and their specific gravity (SG=1.00589 ± 0.00011) calculated. Products with specific gravities similar to semibuoyant eggs were obtained, and tests were conducted on their rates of travel and settling times when exposed to current. Materials with specific gravities slightly greater than semibuoyant cyprinid eggs (SG>1.01) sank too rapidly, while materials less dense than water (SG<1.00) traveled downstream more rapidly than guild members' eggs. Particle size, not shape, noticeably affected rates of travel and settling times. Laboratory and field tests indicated that a modified nylon 12 particle (SG=1.00457 ± 0.00017) most closely mimicked the properties of semibuoyant cyprinid eggs.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663700

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The larval stages ofAmbystoma jeffersonianumandA. maculatumcoexist throughout much of their ranges. Mesocosm studies in field pens indicate that coexistence is due to strong intraspecific density-dependent effects and microhabitat shifts associated with predator avoidance. I used laboratory experiments to determine the limiting resource causing the observed density-dependent effects for each species by separating the effects of food and space. Both species experienced reduced survivorship and altered growth rates at high density and in the presence of heterospecific larvae, confirming results from previous field pen studies. Interspecific interactions are a complex combination of intraguild predation (including cannibalism) and competition. Data from treatments with reduced food and space are consistent withA. jeffersonianumbeing space-limited andA. maculatumbeing a food-limited.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663701

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The feeding ecology of the swan goose (Anser cygnoides) and the white-fronted goose (A. albifrons albifrons) overwintering at Poyang Lake, the largest freshwater lake in China, was studied from 1990 to 1991. The daily patterns of these geese showed differences of the activity categories between species. The energy intakes of these geese were estimated by fecal analysis, daily dropping counts, and calorie determinations. The average daily digestible energy intakes of these geese were about twice their basal metabolic rate. Roots ofVallisneria asiatica, Acorus calamus, andCatessp. were the main food for the swan goose. The leaves ofCarexsp. were the main food of the white-fronted goose. The diets of the geese do overlap with those of some other waterbirds, mainly that of the Siberian crane (Grus leucogeranus) in Poyang Lake. This, however, is not a main reason for the decrease of the number of geese in winter in this season.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663702

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Streams on the island of Guam were surveyed to compare species composition and densities of the most common species among seven rivers, of which three were above a dam and reservoir and three were unregulated. Rivers above the reservoir were also compared to the outflowing river. Species found in all of the rivers included the indigenous gobiesAwous guamensisandStiphodon elegansand two introduced cichlid fishes,Oreochromis mossambicusandTilapia zillii.The gobies have modified pectoral fins that allow them to climb waterfalls and to traverse the spillway and enter the reservoir from downstream. The cichlids, however, are not morphologically adapted for climbing and were introduced to the reservoir; they eventually moved into the rivers. The freshwater shrimpMacrobrachium lar, smaller atyid shrimp of the generaAtyaandCaridina, and the gastropodThiara graniferawere also found above the reservoir, in the outflowing river, and in the unregulated rivers. However, the flagtailKuhlia rupestrisand the neritid gastropods were not found above the dam. In addition, the dam and reservoir appeared to affect the densities of some species. The densities of the mountain gobyStiphodon eleganswere significantly lower in streams above the reservoir than in unregulated streams. However, densities of the prawnMacrobrachium larwere somewhat higher in the streams above the reservoir, possibly a result of the exclusion of the flagtails. The effects of a small dam and reservoir with a spillway on the largely amphidromous fauna of tropical island streams are relatively benign, impinging primarily on species that are incapable of climbing the spillway or that are impeded in upstream migration by the reservoir.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663703

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The Lacanja River, a tropical rain forest river in southern Mexico, remains relatively undegraded and serves as a good reference for comparison with other rivers in the region that are experiencing human impacts. We sampled 12 sites from the headwaters to the mouth of the river (120 km) in both the wet and dry seasons to quantify longitudinal and seasonal patterns in fish community diversity and composition. We collected 44 species (41 native) from the river, with Cichlidae the most speciose family. The most widespread and abundant species wereBrycon guatemalensis, Astyanaxsp. (both Characidae), andCichlasoma intermedium(Cichlidae). Based on fish species composition, the river could be divided into an upper, middle, and lower zone; waterfalls impeded fish movements within and between these zones. The upper zone had the lowest species diversity, and the lower zone had the highest. All of the upper zone fishes also occurred in the lower zone, and community composition changed from upstream to downstream solely through species addition and without species replacement. Overall, species diversity was slightly higher in the dry season.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663704

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Attempts at large river restoration are few and largely experimental. We studied a newly constructed river-wetland project on the upper Mississippi River three years after its completion. Species inventories for fish began to be compiled in the spring of 1993. Coincidentally, record rainfall throughout the midwest resulted in extreme floods and caused flooding of the study area during 1993. Fish communities responded to flooding with increased species diversity immediately following the flood. Wetland habitats yielded eight species of fish prior to flooding in June of 1993 compared to 26 species collected at the same sites in August 1993 following the flood crest. June 1994 sampling caught 33 species, but they declined to 16 in subsequent collections during August 1994. Flooding served to provide at least a temporary increase in diversity.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663705

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The yellow bass (Morone mississippiensis) is native to the Mississippi River drainage and some adjacent Gulf of Mexico tributaries where it inhabits backwaters, oxbows, and reservoirs. We described the diet ecology of yellow bass in an oxbow of the lower Mississippi River, assessed differences in diets between life stages, and measured diet overlap between yellow bass and coexisting species. Indices of diet breadth differed among age groups, with the diet of age-1 yellow bass being more specialized than that of larger fish. Although the yellow bass consumed a wide array of food items, it tended to rely on certain foods during different life stages. Age-1 yellow bass fed on chironomids, amphipods, and fish eggs, which accounted for 84% of the diet by weight. Age-2+ yellow bass consumed fish, fish eggs, amphipods, and benthic insects, which was over 70% of the diet by weight. Diet overlap was not significant (P > 0.20) between age-1 and age-2+ yellow bass, or between age-1 yellow bass and age-0 largemouth bass (Micropterus salmoides), inland silverside (Menidia beryllina), or juvenile bluegill (Lepomis macrochirus), suggesting that exploitative competition did not occur. Nevertheless, interactions between yellow bass and coexisting species may take the form of intraspecific predation given the propensity of the yellow bass to eat fish eggs.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663706

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Total mercury concentrations were determined in two Connecticut lakes for six fish species representing a range of trophic levels—largemouth bass (Micropterus salmoides), chain pickerel (Esox niger), black crappie (Pomoxis nigromaculatus), bluegill (Lepomis macrochirus), smallmouth bass (M. dolomieu), and yellow perch (Perca flavescens). Total mercury concentrations in all fishes increased with length and age. Slopes of log10mercury concentration-age regressions, which were used to compare bioaccumulation rates, were different among species in both lakes. In both lakes, no difference in bioaccumulation rate was found between top-level predators. Top-level predators and intermediate trophic level species (black crappie and yellow perch) accumulated mercury at a faster rate than bluegills. Intermediate trophic level species had bioaccumulation rates comparable to top-level predators over the range of ages sampled. Differences in mercury concentrations between a top-level predator (largemouth bass) and intermediate trophic level species decreased with age, while differences between largemouth bass and bluegill increased with age.

ISSN:0270-5060    

DOI:10.1080/02705060.1999.9663707

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor