An Assessment of Hydroacoustic and Electric Fishing Data to Evaluate Long Term Spatial and Temporal Fish Population Change in the River Thames, UK

This paper reports the results from mobile hydroacoustic surveys carried out between 1994 and 2018, to assess fish stocks in four impounded reaches, covering 19.8 km of River Thames, England. The data are complemented with electric fishing boom boat results, collected at same study reaches time periods. Hydroacoustic used inter-calibrated dual split-beam scientific echosounders, transducers beaming horizontally across river provide abundance distribution estimates. Electric provided catch per unit effort estimates information on size structure species composition. Catch margins were dominated by roach (Rutilus rutilus), bleak (Alburnus alburnus) dominant mid-river. demonstrated patchy spatial distribution, often associated natural anthropogenic habitat features. Cyclical peaks troughs both found. There periods correspondence estimates, but also significant divergence. concept ‘Shifting Baseline Syndrome’ is discussed reference these data, illustrating importance viewing long term quantitative when using meaningful points. potential impact temperature flow population discussed.