W. Waldo Wakefield

Quantitative benthic habitat characterization at Heceta Bank, Oregon

Recent studies have highlighted the shortcomings of regional trawl surveys for quantifying abundance of demersal fishes in rugged habitats. Many species show strong affinities to areas of high topographic relief and rugosity, therefore precluding sampling by bottom trawl gears. Consequently, advanced survey technologies such as submersibles and camera sleds have been utilized to survey demersal fishes in situ. One prerequisite in extrapolating densities of demersal fishes observed in situ is the mapping of benthic habitats beyond the observational extent of submersibles. Habitat characteristics observed from submersible and ROV dives in the late 1980s, 2000, and 2001 were used to establish habitat classes that have been statistically shown to correlate with demersal fish distributions. Those habitat characteristics were then extrapolated over the extent of a multibeam sonar survey conducted in 1998 using quantitative parameters derived from high‐resolution bathymetric and acoustic backscatter data. The re...

Pilot work using a codend video camera for improved acoustic interpretation of backscatter observed during fisheries acoustic surveys.

One challenging but crucial element of fisheries acoustic surveys is accurate groundtruthing of the echo return. Assignment and proportioning of areas of backscatter to the correct species or mix of species affects fish biomass calculations. Typically, survey groundtruthing is done by midwater trawls targeting a single scattering layer of interest. However, the depth at which each species is caught is unknown. Therefore, this method is problematic when multiple scattering layers are present. Small scatters are also missed, which may be important contributors to the echo intensity. To address these issues, we conducted pilot work using a video camera mounted in the codend of an open midwater trawl, which enabled us to look at several scattering layers during each tow. For comparison, we conducted tows with a closed net and no camera at the same location. We then examined each acoustic echogram and the corresponding tow in order to compare backscatter calculations attributable to our species of interest. We...

Identifying Potential Habitats from Multibeam Echosounder Imagery to Estimate Abundance of Groundfish: A Case Study at Heceta Bank, OR, USA

Publisher Summary Over the past 20 years, a growing number of US West Coast fisheries biologists, marine ecologists, and marine geologists have conducted collaborative studies to quantify fish and associated invertebrate populations in the context of their marine habitats. An expanding number of these regional research programs along the US West Coast have formed the basis for a coast-wide network of sites where seafloor mapping and direct observation are supporting ongoing habitat-based groundfish research. Technologies, methods, and classification schemes for mapping marine habitats have evolved and advanced over this period and will continue to do so. Heceta Bank is one of the largest banks off the western coast of North America, extending 55 km from north to south and rising above the continental shelf to 67 m water depth. Due to heterogeneous substrate of varying relief, the bank supports a diverse assemblage of demersal fishes and is an important fishing ground off the coast of Oregon, USA. The top of the bank is comprised of boulders and cobbles eroded from outcrops of sedimentary rocks, while layers of finer grain size material cover the lower relief flanks. Using observations of fish–substrate associations from 19 remotely operated vehicle dives, 57 distinct substrate types and 9 habitat types have been identified. Using this map of potential habitats bank-wide abundance and variance values for a select group of resident fishes have been estimated.