Cost effective sampling of fish populations in large water bodies

ABSTRACT

Estimation of fish population size in large water bodies is a long-standing problem. In addition to sampling difficulties there are economic constraints. Case histories are presented showing how a range of large habitat types have been surveyed and the methods are discussed in terms of success and cost: (a) the status of the River Severn fish population was monitored by postal questionnaires addressed to contest fishermen and proved extremely cost effective; (b) a predator cull and population estimate for a 35 ha lake was made by sequential netting of sections and the nature of the result questioned the validity of a less labour intensive qualitative approach to lake surveys; (c) an electric fishing technique has been developed for surveying canals and comprises a boom-mounted array of ten anodes which gives worthwhile improvement in performance when compared to a few hand-held electrodes; (d) attempts have been made to remove roach from a 240-ha water supply reservoir, using echo-sounding to locate shoals prior to capture with a purse seine.