In New Zealand seas, grey-headed mollymawks breed only at Campbell Island, where they intermingle with the black–browed mollys. They return to the island in early September. They are occasionally seen in New Zealand coastal waters and are one of the most frequently beached of the mollymawk species, especially in July–August when juveniles are moving north into the Tasman Sea. They tend not to congregate about fishing boats as most other mollymawks do.
However, recent research, comparing numbers from the 1940s and the 1990s on Campbell Island in the subantarctic, indicates a severe decline of the grey–headed mollymawk. Between the 1940s and 1990s there was a continuous 82%–88% decrease in nest numbers at three colonies. In the 1940s, there may have been as many as 43,000 grey–headed mollymawk nests per year. But in 1995–97, only 7800 were recorded, less than one–fifth over 50 years! The long–term decline is most likely caused by environmental changes that have an effect on the birds’ food supply. While longlining practices have improved considerably, the impact of the reckless bycatch of albatross in the 1970s and 1980s is still felt today, and the overall food supply for birds is down. Fortunately New Zealand fisheries are now developing methods that reduce the accidental capture of seabirds, but as albatrosses roam the southern oceans in their search for food, they also overlap with unregulated fisheries in international waters.
