Title: Eel and elver studies in the Severn : interim report (256/6/ST)
Author: B. Knights
Author: E. White
Document Type: Monograph
Abstract:
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: Eels; Migration; Biological sampling; Data collection; Weirs; Population decrease; Fisheries
Geographic Keywords: Severn; Severn Estuary; Bristol Channel; Bristol Avon and North Somerset Streams catchment; Parrett; Wye (Anglo-Welsh border)
Extent: 45; + appendices
Permalink: http://www.environmentdata.org/archive/ealit:3897
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