摘要:

This study documented mercury contamination in river otter (Lutra canadensis) in the Keweenaw Bay area, northern Michigan. Total mercury concentrations in liver and kidney from 11 otters were determined by atomic absorption spectroscopy and ranged from 0.79 to 4.07 μg g−1wet weight. There were no significant differences in mercury concentrations between males and females, or between tissue types. A significant difference did exist between mercury levels in mature animals and those in immature animals (<1 year old). Data indicate that otters in areas with no known point sources are contaminated with mercury.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664420

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Wisconsin records forChordodes morgani, Gordius robustus, andParagordius variusare summarized. The occurrence of horsehair worms in the Great Lakes Is reviewed. Sexual size differences are demonstrated InG. robustus, with females being significantly longer than males. Skewing of sex ratios in horsehair worm populations is discussed.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664421

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Weight-length data were obtained for 45 muskellunge (Esox masquinongy) populations (N=4,343) from 16 states to develop a standard weight (Ws) equation that would allow calculation of relative weight (Wr) values. We developed a 75-percentile equation using the regression-line-percentile method. The proposed equation, based on all fish combined, is log10Ws(g) = −6.066 + 3.325 log10TL(mm). The English equivalent for this equation is log10Ws(lb) = −4.052 + 3.325 log10TL(in). This equation is useful for 38 cm and longer muskellunge, and there was no evidence of consistent trends in increasing or decreasingWrwith increasing fish length. Because muskellunge can be sexed based on external characteristics, we also developed separateWsequations for male and female muskellunge. However,Wrvalues calculated with the combined equation were quite similar (Wrvalues within 1–2) to those for values calculated from the female-onlyWsequation. Values calculated with the male-onlyWsequation were slightly more variable.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664422

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We compared cove rotenone sampling and Leslie catch-depletion estimates of age-0 largemouth bass (Micropterus salmoides) abundance in vegetated and unvegetated areas of Lake Guntersville, Alabama, in July—August 1992. With the Leslie catch-depletion method, bass abundance was estimated in 0.05 to 0.32-hectare areas enclosed with a block net. A 4.3-meter direct-current electrofishing boat was able to completely fish each enclosure with five to seven consecutive sampling runs and constant effort. Size-selectivity was not evident as no significant correlations existed between mean length and mean weight at capture for each sampling interval. In addition, catchability remained constant over time. In a cove that contained Eurasian watermilfoil (Myriophyllum spicatum), we estimated 1,088 age-0 largemouth bass/hectare from the two electrofishing catch-depletion samples compared to 1,386 bass/hectare by subsequent rotenone sampling. Cove rotenone density and biomass estimates in four unvegetated coves (1.2-hectare each) averaged 86 age-0 largemouth bass/hectare and 0.52 kg/hectare and were not significantly different from electrofishing catch-depletion density and biomass estimates which averaged 104 bass/hectare and 0.78 kg/hectare. This method appears to be a reliable and less costly method than cove rotenone sampling to estimate abundance of age-0 largemouth bass.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664423

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We determined spatial and temporal feeding patterns of white perch (Morone americana) and yellow perch (Perca flavescens) in Lake Erie by analysis of stomach contents. Diets were compared across years (1983–1985), seasons, basins of the lake (western and central), and depth in the western basin. Diets of these two fish species were generally similar, although white perch tended to use more zooplankton, while yellow perch consumed more Chironomidae, Sphaeriidae, and fishes. In other instances, competition apparently led to resource partitioning that resulted from differences in ontogenetic feeding requirements and mouth position between white perch and yellow perch.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664424

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We studied the feeding dynamics of young-of-year (YOY) brown trout (Salmo trutta) inhabiting stream-margin habitat of a mountain stream during August and September. We found invertebrates in fish stomachs throughout 24-h sampling periods. The abundance of items in stomachs increased with the density of drifting invertebrates after dark. Composition of stomach contents and composition of drifting invertebrate samples were related, but Ephemeroptera larvae had positive electivity indices more frequently than other taxa. The mean lengths of invertebrates in stomachs were greater than those in samples of drifting invertebrates.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664425

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Many moribund and dead fish were found drifting in the main channel of the Mississippi River during late winter. A total of 3,574 fish representing 37 species were collected with an effort of 214 net-days in the tailwater habitat below Lock and Dam 13 and Lock and Dam 14 of the Mississippi River during February 1984 and March 1985. Bluegill (Lepomis macrochirus). channel catfish (Ictalurus punctatus), pumpkinseed (Lepomis gibbosus), freshwater drum (Aplodinotus grunniens), and gizzard shad (Dorosoma cepedianum) were the most abundant species, composing 87% of the total catch. Most of these were small fish, probably age 0 or age 1. Catch was not correlated with discharge, but was related to location of the net in the channel with more fish collected near the shores than the center.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664426

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

I described pupal chamber location, construction, and larval size relationships of the dobsonfly,Corydalus comutus, from 72 larvae collected in 1988 and 27 pupae in 1990. Larvae constructed pupal chambers beneath a variety of objects and debris (55% of which was man-made refuse). Anatomical measurements of pupae indicated sexual dimorphism; generally, males had significantly wider head capsules (P = 0.01) and longer mandibles (P = 0.01) than females. Significant correlations (P<0.05) were observed between larvae and pupae sizes and chamber sizes. Proper location and construction of pupal chambers can minimize the effects of adverse environmental factors.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664427

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Populations of sculpin (Cottus cognatus) were altered to create stream sites with increased and decreased fish density. Subsequently, the response of benthic insect species was observed. Sculpin predation appeared to have little or no effect on size distributions and secondary production of most benthic invertebrates. However, densities of some trophic groups increased by two- or three-fold following reductions of sculpin densities. Within sites of sculpin removal, densities of gatherer/scrapers were twice those of addition or reference sites. Densities of total insect populations in reduction or reference sites were two to three times greater than those in the addition sites. Several trophic groups, particularly scraper/gatherers, showed the highest densities in sites of unaltered sculpin densities. Filter-feeders presented a third response to the manpulated sculpin populations; their densities increased with increased sculpin density. This suggests a negative sculpin influence on competitors of filterers.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664428

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The Asiatic clam (Corbicula flumineaMüller) was found in Arapahoe County, Colorado. This is the first record of this exotic clam from the state of Colorado.

ISSN:0270-5060    

DOI:10.1080/02705060.1994.9664429

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor