Development of sampling regimes for estimating density of red sea urchins (Strongylocentrotus franciscanus)

Uncertainty in stock biomass estimates of marine invertebrates arises, in part, due to difficulties in obtaining accurate and precise density estimates. In aggregated populations, such as with red sea urchins (Strongylocentrotus fianciscanus), a precise estimate of density may be quite challenging to obtain. I examined different survey designs using simulated urchin populations with the objective of improving density estimation. I evaluated alternative designs in terms of precision, cost, and bias. Designs under consideration were a simple version of random transect sampling, and more complex random transect sampling designs, including restricted adaptive cluster sampling and a design stratifying by substrate within the transect. The complex designs were more precise and cost-efficient than the current sampling method used in British Columbia but produced slightly biased estimates. Choice of sampling designs for use in field surveys, which are conducted by SCUBA divers, may be influenced by the ability to implement complex designs.