Relationships between the population and feeding ecologies of the diving ducks and fish of Lough Neagh, Northern Ireland: a synthesis

Winfield, Ian J. and Winfield, Denise K. and Davidson, Robert D. (1997) Relationships between the population and feeding ecologies of the diving ducks and fish of Lough Neagh, Northern Ireland: a synthesis. MAGYAR VÍZIVAD KÖZLEMÉNYEK, 3. pp. 263-283. ISSN 1416-1389 (nyomtatott); 1419-6107 (elektronikus)

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Abstract

Lough Neagh is a large (surface area 387 km2), eutropliic. (long-term annual mean total phosphorus 107 mg l'1) lake in Northern Ireland, U.K., which supports large overwintering populations of the diving ducks Common Pochard (Aythya ferina ), Tufted Duck (Aylhya fuligula ), Greater Scaup (.Aylhya mania ) and Common Goldeneye (Bucephala dongnia ) (approximate densities of up to 100, 90, 6 and 26 individuals krn C respectively). An examination of long-term population trends between 1965 and 1988 revealed that the abundance of Common Pochard and scaup had been relatively stable and Goldeneye had shown a recent increase. In contrast, the numbers of overwintering Tufted Duck had declined markedly dunng the early 1980s, but recovered to former levels in the winter of 1987/1988. These latter changes were subsequently (bund to mirror those in the abundance of roach (Rutilus mfilus), a cyprinid fish which was first recorded in the Lough Neagh system in 1970. After its introduction, the roach rapidly increased in abundance before declining in the late 1980s, probably due to heavy infestation by the cestode tapeworm Ligula intestinalis. Studies carried out in the late 1980s, when the roach population was in a state of relative decline, showed that the diets of the above diving ducks and the major fish of the lough (i.e. roach, perch Perca fluviatilis, pollan Coregoms autumnalis (Pallas) and eel Anguilla anguilla) showed relatively high overlaps due to the common consumption of chironomid larvae. However, three major groupings were apparent. Common Pochard, Greater Scaup, Common Goldeneye and eel fonned a group with diets dominated by chironomid larvae, while perch and pollan formed a smaller group in which the crustacean Mysis relicta Loven was an important dietary component. Tufted Thick and roach formed a third and distinct group in which molluscs, particularly Valvata piscinalis (Muller), were important in the diet It is suggested that the feeding ecology of Tufted Duck and roach in Lough Neagh forms an example of distant competition which may be responsible for the observed fluctuations in the numbeis of overwintering Tufted Duck. Consistent with this hypothesis, during the early to mid 1990s the roach population has remained low in abundance and the numbers of Tufted Duck have remained high The strengths and weaknesses of this interpretation, and those likely to be met in any study of competition between ducks and fish, are discussed.

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