The littleneck clam, Protothaca staminea, as a tool for potential oil pollution assessment: Part 1—density of stock

Abstract

Littleneck clams, Protothaca staminea, were sampled on two plots in the north Puget Sound region to evaluate the effects of sampling strategy on costs for measuring plot density in an hypothesis-testing framework. The general approach involved quadrat sampling on permanently marked plots. Results indicated that detection of differences in density as small as 10% with 80% probability would: (1) exceed in cost the economic value of 10% of the stock and (2) decimate more than 10% of the stock unless provision were made to allow survival of sampled clams. Restriction of sampling to the marketable cohort, restriction of sampling to parts of plots covered by vegetation, increasing the probability for a Type I error and use of a smaller quadrat size all served to substantially reduce sampling costs. The projections of sampling requirements were made using estimates of variance obtained from sampling in differing manners and at different seasons. The estimates so obtained did not give good uniformity. This has an important ramification for pollutant studies because a common variance for control and ‘polluted’ means is an assumption central to the use of probability models.