Use of telemetric tracking to examine environmental influences on catch/effort indices. A case study of Atlantic Salmon (Salmo salar L.)in the R. Tywi, S. Wales

• Main Authors: Clarke, D., Purvis, W.K., Mee, D.
• Format: Book
• Language: English
• Published: National River Authority Wales 1990
• Subjects: Ecology; Fisheries; Limnology; UK; Wales; Rivers; Salmon fisheries; Salmo salar; Tagging; Tracking; Stream flow; Fish catch statistics; Migrations; Environmental Monitoring; Atlantic salmon
• Online Access: http://hdl.handle.net/1834/25218

A case study of Atlantic Salmon runs into the R. Tyvi (S. Wales) is presented. Radio tracking of over 200 salmon in 1988 and 1989 has demonstrated that flow is an important factor in modifying both run timing and migratorysuccess. Entry of salmon into the river is typically in response to flow events, and periods of low falling flows delay entry and may directly result in reduced runs into the river. Delayed entry may also increase the proportion of the run migrating after the end of both rod and net fishing seasons.The implications of these results for net and rod catch and catch/effort data are discussed, using both statutory reported catch data and data from specific catch/effort studies. Flow is demonstrated to be a dominantfactor in determining the within-season distribution of rod catch and catch/effort during low-flow years. Estuarial seine net catch and catch/effort tend to be controlled more by time of return than by flow although low flows may delay runs. Annual reported rod catch is correlated with flow, which controls in season availability, catchability andconsequently the amount of fishing effort. Use of catch or catch/effort data should take account of inter-year variations in flow and other environmental factors. Although catch and catch/effort are valuable indicators of fishery performance, they are inadequate to representchanging stock levels. Environment Agency Archives North West + figures