Harvey et al.: improving the statistical power of length estimates of reef fish 
79 
in visual surveys of reef-fish length can potentially save 
both time and money on field costs. However, when the 
goal of the program is to detect larger changes, the advan- 
tages of a stereo-video system are not so great owing 
to the time needed to calibrate the system and analyze 
stereo images after the data are recorded (Harvey and 
Shortis, 1998). 
Acknowledgments 
We acknowledge financial aid from the New Zealand 
Department of Conservation (research grant 1822), the 
University of Otago Research Committee, the Southland 
Regional Council (New Zealand) and the Division of Sci- 
ences at the University of Otago, Dunedin, New Zealand, 
and from Sony New Zealand Ltd, THC Milford 
Sound, Fiordland Lobster Company, and Mobil 
and Gore Services Ltd. We are grateful to James 
Seager, of the Department of Geomatics at the Uni- 
versity of Melbourne, for assistance with software 
development, and to June Hill, Callum Duncan, 
Lisa Keiieher, and Andrea Brown for assisting with 
field trials and to all the divers who willingly gave 
their time to assist with this research. We would 
also like to acknowledge Glenn Carbines and the 
Fisheries Division, National Institute of Water and 
Atmospheric Research, for allowing us access to 
data. This manuscript was greatly improved by 
comments from Howard Choat, June Hill, Philip 
Mladenov, Keith Probert, and four anonymous 
reviewers. 
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