Gill Caradoc-Davies of Portobello asks :-
Living on Otago Peninsular for 15 years I have noticed over the past three years that there has been no swarming of Munida (scarlet shoals) and no Peruvian mackeral in the harbour. Is this connected with global warming?
John Jillett, marine biologist retired from Otago University's Portobello Marine Laboratory, responded.
You are most probably correct that these changes are related to global warming. Both Munida and Peruvian jack mackerel are typical of cool temperate, southern hemisphere coastal waters. Munida in particular typically occurs only in a circumpolar subantarctic zone that includes coasts of the southern tip of South America, the Falkland, Kerguelan, Auckland and Campbell Islands, but not at South Georgia or around the Antarctic continent.
Both species appear close to their northern limits of distribution in southern New Zealand where it is not normally found north of Cook Strait, nor is it found in Tasmania or southern Africa.
Records of the distinctive scarlet shoals of Munida from the Portobello Marine Laboratory over the past 100 years show that, up until the late 1990s, there were only occasional years when they were absent in summer. Usually the shoals first appeared in October/November and were common throughout Otago Harbour and open coastal seas until February/March.
During the past 10 years Otago Harbour sea surface temperatures have generally been significantly warmer than the long-term average (1953 – present). The only sightings of Munida in these same 10 years were on 14 days in the summer of 2001-2002 and 19 days in the summer of 2003-2004. Sea surface temperatures in these two summers were cooler than others in the same period.
If present global warming trends continue, both distinctive species, Munida and Peruvian Jack Mackerel, are likely to disappear from southern coastal seas of New Zealand’s South Island.