摘要:

AbstractWe investigated habitat specificity of the amber darter (Percina antesellaWilliams&Etnier 1977), an imperiled fish from restricted portions of 2 rivers in the southeastern United States. Foraging amber darters occupied a narrow range of riffle habitat, consistently avoiding areas<20 cm deep and with velocity<10 cm. s−1near the substrate, occupying areas with cobble or gravel substrate and average water‐column velocity of 30 to 70 cm. s−1. During low to mo'derate flows, approximately 20% or more of the study areas contained suitable habitat for the species. Amber darters appeared rare, and the numbers of individuals were uncorrelated with the concurrent availability of suitable habitat. Protecting the amber darter may require more than maintaining adequate depths and velocities over gravel‐cobble substrates. Until we understand the potential importance of migration and dispersal for maintaining small populations, suitable habitat should be maintained over the longest contiguous stream segments p

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1994.tb00106.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractTo study the effects on a stunted freshwater population of Arctic charr,Salvelinus alpinus(L.), two groups of large (26–45 cm) individually tagged brown trout,Salmo truttaL., were released and recaptured with gillnets after 1, 7, 11 and 63 weeks. One group of trout was trained on a fish diet before release, and the other, reared on commercial dry pellets, served as a control. Specific growth rates in both groups were negative 1 week after release and approached zero after 63 weeks. Condition factor and internal fat content decreased during the experiment. Although only 11% of the trout stomachs examined contained fish prey, charr represented 79% of the total stomach weight content. Gillnet samples of charr before and 63 weeks after the release of trout indicated a decreasing population size of charr. Individual growth and mean length of charr increased after release of trout, especially for charr at age 4 years. After the release of trout, 35% of the charr were longer than 20 cm as compared with 6% before the releas

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1994.tb00107.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractPatterns of growth and size achieved in freshwater fish are examined with relation to the issues of indeterminate and determinate growth and asymptotic growth. Various authors suggest minimum, average and maximum sizes attained by fish, variously pointing to very small gobies and very large sharks, with most fish being about 150 mm long. Growth in fish is distinctive in that typically it continues throughout life, even though it becomes slower with increasing age and the onset of sexual maturity. Growth rates and size achieved by fish are highly flexible and subject to both genetic and environmental controls, so that size reached may vary with environmental variables such as water temperatures and food availability (both food abundance and prey types and sizes). Frequency distributions of 5 disparate freshwater fish faunas (Papua‐New Guinea 267 species and tropical; North America 709 species and subtropical to Arctic; Australia 176 species and tropical to temperate; New Zealand and Great Britain 27 and 39 species and both warm to cool temperate) closely resemble distributions generated by the theoretical model of Hutchinson&MacArthur, and also data on diverse faunas. Frequency distributions in these faunas are closely similar, with a majority of species being small. This similarity would seem to suggest a general explanation. However, examination of the freshwater fish fauna of North America suggests that, rather than showing a predominance of large fish in the Arctic, the fauna has more large fish towards the tropics, though the proportion of large fish there is lower owing to the proliferation of small species in the tropics and a paucity of them towards the Arctic. Analysis shows a shift in the size composition of the fauna with latitude and shows that the general pattern for the whole of North America consists of a composite series of rather different patterns. This suggests that there is probably no meaningful general explanation of the overall patterns seen in these diverse and disparate faunas and that the similarity in overall size distributions between freshwater fish faunas of North America, New Guinea, Australia and New Zealand are of little ecological or evolutionary significance. The generality of Cope's rule is questionable, especially for fish, in which dwarfing and/or evolution towards smaller size are seen to be common phenomen

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1994.tb00108.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe influence of physical watercourse parameters on the degree of anadromy was studied in 15 lake populations of Arctic charr (Salvelinus alpinus(L.)) in northern Norway. The anadromy of the different populations was scored based on the following criteria; marine parasites. fish length and length at maturity. There were significant negative correlations between the anadromy scores and both the length of the outlet rivers of the different lakes and a migration barrier index for the different watercourses (combining migration distance and water velocity). It is hypothsized that these correlations were due to differences in energy expenditure for charr during upstream migration and/or differences in predation pressure on charr during river migration. Short rivers with relatively high water velocity seem to be the most preferable conditions for the anadromous life‐history strategy. There were no correlations between the degree of anadromy and mean river slope or minimum summer water discharg

ISSN:0906-6691    

DOI:10.1111/j.1600-0633.1994.tb00109.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY