Fish-removal from lakes increases food for waterfowl.

Abstract

Research by the Game Conservancy wetland research group at Great Linford, United Kingdom from 1986-1989 concentrated on the potential competition for food between fish and waterfowl in gravel pit lakes. The aim of the work was to improve duckling survival on restored sand and gravel pits. Food availability for waterfowl (benthic invertebrates and water plants) was monitored during 1986 and 1987 with fish present before a major draw-down and fish-removal in October 1987. A total of 6.6 tonnes of fish Abramis brama (bream), Rutilus rutilus (roach), Perca fluviatilis (perch), Tinca tinca (tench) and Esox lucius (pike) was caught.
Monitoring continued in 1988 and 1989. Large increases in macrophyre and invertebrate standing crops and invertebrate diversity occurred in the study lakes. The peak biomass of chironomid larvae trebled in the Main Lake from 3-9 g dry weight/square metre and the peak summer macrophyte standing crop increased 53-fold subsequent to fish-removal.
In 1988, 1989 and 1990 Anas platyrhynchos (mallard) and Aythya fuligula (tufted duck) with young duckling broods used the lakes that did not contain fish as feeding habitat much more than in previous years. There are early indications that tufted duckling survival on the lakes has improved over past years.
Wintering Anas strepera (gadwall), Aythya ferina (pochard), Cygnus olor (mute swan), and Fulica atra (coot) numbers also increased on the lakes without fish.