New Zealand Journal of Marine and Freshwater Research abstracts

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Two-phase stratified random surveys on multiple populations at multiple locations

Bryan F. J. Manly

Western Ecosystems Technology Inc.
2003 Central Avenue Cheyenne
WY 82001, United States
email:bmanly@compuserve.com

Jo-Anne M. Akroyd
Kim A. R. Walshe

Akroyd Walshe Ltd
P.O. Box 28 814
Auckland, New Zealand
email: jakroyd@attglobal.net

Abstract   The two-phase random stratified sampling design proposed by Francis (1984) was designed for situations where prior information is insufficient to ensure an efficient allocation of sampling effort to different strata. It involves taking a first-phase sample, and then using the data from this to allocate a second-phase sample which compensates for any shortcomings of the first-phase sample. Here we generalise this method to situations where several species are sampled simultaneously, and at several locations. The method then uses the first-phase sample results to decide how best to allocate a second-phase sample to locations and strata. We provide the results of a simulation study based on model populations of shellfish which demonstrates the effectiveness of the method. We use a survey of cockles, pipis, and tuatuas on 11 Auckland Fisheries Management Area beaches as an example of its use.

Keywords   stratified sampling; shellfish; two-phase sampling; New Zealand

M01036 Received 7 May 2001; accepted 26 January 2002; published 17 September 2002
New Zealand Journal of Marine and Freshwater Research, 2002, Vol. 36: 581-591
0028-8330/02/3603-0581 $7.00 © The Royal Society of New Zealand 2002

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