The ecology of the overwintering diving ducks of Lough Neagh, with particular reference to their interactions with the fish populations

Abstract

The ecology of the overwintering diving ducks pochard, tufted duck, scaup and goldeneye on Lough Neagh was investigated during the winters of 1987 /88, 1988/89 and 1989/90. Long-term population trends were assessed by the analysis of count data from 1964/65 to the present. Abundances of pochard, tufted duck, and goldeneye changed markedly over this period, with a decline in the early 1980s most marked in the tufted duck, and an upward trend over the last six years.

The daytime distributions and activities of the ducks around the lough were investigated. Pochard, tufted duck and scaup were nocturnal, while the goldeneye was diurnal. Tufted duck and goldeneye had the highest spatial overlaps and also the most diverse diets. Dietary overlaps among the ducks were high due to the predominance of chironomid larvae, but significant differences were also demonstrated with molluscs particularly important for the tufted duck. Species-specific size selectivity patterns were also found.

Habitat and dietary overlap between the ducks and the major fish populations were established and recent declines in the abundances of perch, roach and eel were shown to correlate with increases in the numbers of overwintering ducks. A fish-waterfowl competition hypothesis was examined further by assessing variations in depth distribution, abundances and availability of benthic macroinvertebrates, which were dominated by chironomid larvae and oligochaetes. A speculative assessment was made of the impact of the ducks on the benthos, and the four species were estimated to consume approximately 39% of the overwinter decline in the standing crop of chironomid larvae.

It was concluded that competition may be occurring between the fish and duck populations, particularly between tufted duck and roach for molluscs. Additional evidence for the existence of this interaction may arise from future changes in the abundance of the roach population.

Date of Award	Sept 1991
Original language	English