Accuracy of the Patch model used to estimate density and capture efficiency in depletion experiments for sessile invertebrates and fish

Hennen, D., Jacobson, L., and Tang, J. 2012. Accuracy of the Patch model used to estimate density and capture efficiency in depletion experiments for sessile invertebrates and fish. – ICES Journal of Marine Science, 69: 240–249. The Patch model is used to analyse depletion experiment data for sessile invertebrates and fish that do not randomize after sampling. Simulations indicate that density and capture efficiency estimates were useful under realistic conditions for Atlantic surfclam (Spisula solidissima) and many other sessile demersal species. Density estimates were generally biased low by position-data errors, whereas efficiency estimates were relatively unbiased. A new "hit" matrix method improved the accuracy of efficiency estimates, reduced the variability for efficiency and density estimates, and simplified assumptions about the movement of organisms after sampling. Depletion tows should be spaced to cover the entire study area and to intersect in areas where densities are not low. Model estimates can be made for individuals fully or partially selected by the sampling gear, and information about size selectivity is useful. Patch-model estimates can be used to calculate swept-area abundance or biomass, estimate catchability coefficients for survey or catch per unit effort data, form prior distributions used in stock assessment models, and estimate efficiency for other types of sampling gear.