New Zealand Journal of Zoology abstracts
Z00023Received and accepted 17 July 2000
What limits the harvest of sooty shearwaters (Puffinus griseus) on
Poutama Island?
P. O'B. LYVER
Department of Zoology
University of Otago
P.O. Box 56
Dunedin, New Zealand
Present address: Natural Resources Institute, University of Manitoba, Winnipeg,
Manitoba, Canada, R3T 2N2.
Abstract The traditional harvest of sooty shearwaters by
Rakiura Mäori was studied in the 1994 and 1995 muttonbirding season on
Poutama Island, New Zealand. Chicks were captured much faster during the
rama (the second phase of the harvest when chicks are caught at night on
the surface) than during the nanao (the first phase of the harvest when
chicks are extracted from breeding burrows during the day). Harvest rates
(mins/chick) decreased, and strike rates (chicks/burrow) increased in areas and
years with higher chick density. The relationship between strike rates and
chick density was curvilinear, so observed changes in harvest rate will not be
directly proportional to the actual change in density on Poutama. Burrow
occupancy was highest in areas with intermediate burrow entrance densities,
perhaps because crowding at higher density reduces breeding success, or because
harvest is most intense in high density areas. A 20 year record of captures on
Poutama showed that the harvest rates almost doubled between 1989 and 1998. The
muttonbirders were able to compensate slightly for decreased catches by working
an extra 31 minutes per day during the nanao, but there is little scope
for further compensation on Poutama because the working day is taken up almost
entirely by catching and processing chicks. Density is the main indirect
determinant of the number of chicks that can be gathered on Poutama. The number
harvested is determined directly by how many chicks a muttonbirder can catch
and process in a day on Poutama. Replicate studies are now needed on other
islands to test whether similar limits operate elsewhere.
Keywords sooty shearwater; Rakiura Mäori; harvest rates;
strike rates; chick density
New Zealand Journal of Zoology, 2000, Vol. 27: 395-414
0301-4223/00/2704-0395 $7.00/0 (c) The Royal Society of New
Zealand 2000
PDF file of entire paper: medium quality (1045K); (scanned from paper original: notes about this process)
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