The Populations, Growth and Production of Fish in Four Small Streams in Southern England

The fish populations in one soft water and three hard water streams were investigated to determine their growth and mortality rates and, from these parameters and population estimates, their annual production. Previous workers have usually confined their attention to a single species (Ricker Allen 1951; Johnson Watt 1960; Gerking 1962; Warren et al. 1964; Chapman 1965 and Libosvarsky 1968) although Mann (1965) computed the annual production of five species of fish in the River Thames at Reading. In our studies the annual production of the more abundant fish were estimated at each site, the species involved being trout (Salmo trutta L.), salmon (S. salar L.) bullhead (Cottus gobio L.), minnow (Phoxinus phoxinus (L.)), three-spined stickleback (Gasterosteus aculeatus L.) and stone-loach (Nemacheilusbarbatula (L.)). The eel (Anguilla anguilla (L.), brook lamprey (Lampetraplaneri (Bloch)) and, very occasionally, pike (Esox lucius L.) were also caught, but no attempt was made to measure their growth and production. Production is here defined as the total quantity of fish flesh elaborated in a year, regardless of whether or not all of it survives to the end of the year (Ivlev 1966). The units used are grams fresh weight per square metre of stream bed per year. The paper is based on data collected during the period April 1964-June 1967, but the duration of study at any one site never exceeded 2 years (Table 1). Where data on population densities and growth are available for more than 1 year, these have been combined to give mean production estimates for that site.