Foveaux Strait dredge oyster (Ostrea chilensis) population and bonamia surveys, October 2002 / K.P. Michael, A. Dunn, B.K. Diggles, J. Forman.

NIWA project OYS2002/01

The October 2002 Foveaux Strait oyster survey was a joint programme between the Bluff Oyster Management Company and NIWA. The survey was successfully completed between 16 and 29 October, sampling on 11 days at an average of 16 stations per day. Sea conditions were good for dredge sampling and all dredge tows were less than 80% full, indicating effective sampling. The operational procedure was comparable to that of previous surveys. The sampling design was similar to the 2001 oyster survey with sampling focused on the commercial areas designated by oyster skippers. Designated commercial, exploratory, and background areas were stratified with a number of small strata to spread the sampling effort more widely. Proportionately more stations than for previous surveys were allocated to exploratory and background strata to provide better information on the distribution of oysters and infection by Bonamia exitiosus. Of the 160 stations allocated, 155 first and second phase stations were sampled for relative oyster density to estimate population size. Five of these stations either could not be sampled in the strata or were in background areas where the time required to sample replacement stations exceeded the gain in value to the survey. Oyster samples were collected from 80 stations to determine the distribution of prevalence and intensity of infection by B. exitiosus.