摘要:

ABSTRACTAnnual electro fishing surveys were carried out over an 11‐year period at five sites on an upland river, which was subject to dredging operations in connection with a land drainage scheme. Four of the sites were dredged 3 years after the start of the survey and one control site remained undredged throughout. The results indicated that dredging operations initially reduced Salmonid densities and that there was subsequently a progressive downstream recovery, with fry densities taking up to 6 years to improve at the most downstream site. Yearling and older fish recovered to pre‐drainage scheme levels more rapidly than fry.Changes in population structure were also observed at three of the dredged sites. Two sites were considerably deepened and finally contained larger numbers of older fish than prior to the drainage scheme. The opposite effect was found to have taken place at a site, which became shallower as a result of drainage works, and contained larger numbers of fry at the end of the survey.Increased fish growth rates were also observed at all sites over the experimental period, and this may have been correlated with enrichment of the river system by leaching from increased fertilizer usage within the catchme

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1983.tb00049.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTThe freshwater clupeidLimnothrissa miodonwas transplanted with success from Lake Tanganyika to Lake Kivu during 1958–1960. An artisanal fishery to exploit the clupeid stock started in the beginning of 1980. Based on the results of this artisanal fishery a minimum sustained yield of 4,000 tons/year was estimated for the Rwandese territorial waters of Lake Kivu. Biological research revealed information about growth rate, condition factor K, fat content, migration, distribution and reproduction ofLimnothrissa. An obvious relation was found between fat content and sexual activity with the seasonal fluctuations of plankton production. The main spawning peak coincided with a plankton bloom caused by the turnover of the lake at the end of the dry season in September. At that time a small percentage of the clupeids had fat in their body cavity. It is stated that horizontal migration is mainly induced by reproduction, while the vertical migration is determined by feeding habits. Socio‐economic benefits of the artisanal fishery using trimarans and lift nets were compared with those of the semi‐industrial purse se

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1983.tb00050.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

ABSTRACTIn connection with population work on lampreys at Loch Lomond, a variety of methods of marking ammocoete larvae were evaluated. These included the subcutaneous injection of various coloured marker substances by hypodermic needle and by jet inoculator, the bulk immersion of animals in dyes and the clipping of fins. Mercuric sulphide and colored liquid latex, introduced subcutaneously by hypodermic injection, were found to be the most successful methods, and various colours of liquid latex (Diptex 319) (which had several advantages over mercuric sulphide) were chosen for use in the field.

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1983.tb00051.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1983.tb00052.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1983.tb00053.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:1355-557X    

DOI:10.1111/j.1365-2109.1983.tb00055.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY