A spatial simulation approach to hydroacoustic survey design: A case study for Atlantic menhaden

Abstract

Patchily distributed pelagic fish species present a challenge to classical approaches to hydroacoustic survey designs. We propose a spatial simulation approach to designing acoustic surveys and provide a case study in the northern resident stock of Atlantic menhaden Brevoortia tyrannus during winter. The structure and abundance of this stock is poorly characterized due to a paucity of fishery-independent surveys and the geographically limited range of the reduction fishery. In order to develop new fishery-independent information for this stock, we conducted a simulation study to estimate the accuracy and precision of an offshore hydroacoustic survey. We simulated a spatial super-population based on fishery-dependent data, and randomly re-sampled the population with various types of hydroacoustic survey equipment. Our results suggest that a combination of down-viewing echosounder and omni-directional sonar can generate biomass estimates with a coefficient of variation around 25%. The use of down-viewing echosounder alone, however, generated biomass estimates with poor precision. Our approach accounts for the patchy spatial distributions of the survey populations, which leads to more realistic estimates of precision than classical approaches implicitly assuming independence. The approach also evaluates several types of hydro-acoustic survey equipment in deriving absolute biomass estimates, and the survey, once implemented, may contribute to improved spatially explicit management of the stock.