Status and management of black swans Cygnus atratus, Latham at Lake Ellesmere since the 'Wahine' storm, April 1968

The "Wahine" Storm in April 1968 destroyed the beds of aquatic macrophytes in Lake Ellesmere, South Island, New Zealand and the resident population of black swans (Cygnus atratus) has since declined by at least 75%. Extensive breeding failure, poor cygnet survival, increased adult mortality, and permanent emigration, all responses to the diminished food supply, and intensive hunting, have contributed to this decline. The population in January 1978 was estimated to be 9500, only one-third of which was less than 10 years of age. It is predicted that over the next four years the breeding component of the population will decline by about 50%. The methods by which the North Canterbury Acclimatisation Society has managed the swan population before and since the storm are discussed and suggestions for future management made.