The Chatham Island shag (Leucocarbo onslowi) and Pitt Island shag (Stictocarbo featherstoni) are both endemic to the Chatham Islands, New Zealand. Both species are classified as Nationally Endangered, and moderate to high risk from fishing has been identified to both species, mainly from poorly observed setnet and pot and trap fisheries.
While there is little knowledge on the breeding biology and life history of these species, two censuses have been conducted to count the number of breeding pairs. The first systematic census was conducted from October 1997 to January 1998, and found 842 pairs of Chatham Island shags and 729 pairs of Pitt Island shags. The second census was conducted from October 2003 to January 2004, and found 271 pairs of Chatham Island shags and 547 pairs of Pitt Island shags. This represented declines of 68% and 25% for Chatham Island and Pitt Island, respectively, over a six year period. However, it was unclear as to whether differences in methodology or inter-annual variability in breeding may have influenced these findings.
This study sought to conduct a complete recensus of Chatham Island and Pitt Island shags in such a way to maximse comparability with the earlier counts in order to determine any trend in population size, as well as to investigate the effects of timing and methodology on colony counts, and make recommendations for future monitoring of the populations of Chatham Island and Pitt Island shags.
This report was commissioned by the Department of Conservation, Project MSCPOP2010-02
By I. Debski, M. Bell, and D. Palmer