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Title: Eel and elver studies in the Severn : interim report (256/6/ST)
Author: B. Knights
Author: E. White
Document Type: Monograph
Studies of the Severn elver runs and fishery were carried out by questionnaires, visiting elver stations, observation and hand-net fishing. Little detailed quantitative information was forthcoming from fishermen or elver stations. Mark and recapture studies had to be abandoned because of practical problems and to avoid confusions with a study being conducted by Bristol Channel Fisheries. Information released about this study show recapture rates were very low, suggesting fishing efficiency was low. Results and observations show the elver catch was very poor in the 1991 season. The situation was confused by abnormal migration and hence catching patterns due to adverse weather, spate and water temperature conditions. Twenty traps were designed, built and installed at 10 sites on the Severn and Avon to study upriver migrations. Relatively few elvers were caught at the normal tidal limits at Tewkesbury but they continued to arrive in waves throughout the summer. Large numbers were also trapped at Stanchard Pit, 3.5km upstream of Upper Lode where a branch of the Severn meets the Avon. Most of these had probably been carried up the estuary by tidal transport and managed to scale Upper Lode. Elvers can be carried over this weir by exceptional spring tides but none appeared to be high enough for this to happen in the 1991 season. Very few elvers subsequently reached the next weirs up the rivers. Laboratory and field studies indicate differences in trap efficiencies due to location, currents and climbing media. Plans for further studies using present and commercially available designs are outlined. Elvers and juveniles have been successfully marked using sub epidermal injections of acrylic paint. Recapture rates via traps have been very low. All but one occurred at the first trap above point of release, however, indicating few have been able to by-pass trapping sites. Studies are outlined which should yield more information in 1992. It is concluded that the current project targets have been met. Future plans regarding additional data acquisition and processing and for 1992,93 field and laboratory work are outlined.
Publisher: National Rivers Authority
Publication Place: London
Subject Keywords: EelsMigrationBiological samplingData collectionWeirsPopulation decreaseFisheries
Geographic Keywords: SevernSevern EstuaryBristol ChannelBristol Avon and North Somerset Streams catchmentParrettWye (Anglo-Welsh border)
Extent: 45; + appendices
Total file downloads: 34

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