LONG-TERM GOALS Fish aggregation is important in terms of biology, fisheries, and measurement, quantitative analyses of gregarious movement behaviors remain relatively rare (Turchin 1989). Fish aggregation has most often been studied in easily accessed fish or fish easily maintained in the laboratory such as minnows and dace (see a review in Pitcher and Parrish 1993). Measurements of fish aggregations are often difficult, particularly in pelagic environments. Our goal is to develop new acoustic techniques that have the potential to serve as measurement tools to quantify this ubiquitous and important behavior. OBJECTIVES This project brings together a team with expertise in acoustics, engineering, biology, fisheries, and oceanography to develop and apply acoustic techniques to measure schooling in pelagic fish. We combined traditional, split-beam fisheries echosounding techniques and direct sampling with new acoustic techniques and new platforms in a study area monitored by an existing operational ocean

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Korneliussen, R. J., Heggelund, Y., Eliassen, I. K., Øye, O. K., Knutsen, T., and Dalen, J. 2009. Combining multibeam-sonar and multifrequency-echosounder data: examples of the analysis and imaging of large euphausiid schools. – ICES Journal of Marine Science, 66: 991–997. The first high-resolution, quantitative, multibeam sonar (Simrad MS70) ever developed was mounted in a keel of RV “G. O. Sars” with port-orientated beams. Each ping samples a volume of 60° horizontally × 45° vertically with 500 beams, which is often enough to insonify a complete school of fish or zooplankton. The large amount of resulting data is efficiently preprocessed with automatic, real-time detections of school candidates; these are accepted or rejected during post-processing. The system was used on the continental shelf near the Subantarctic island of South Georgia to study Antarctic krill (Euphausia superba), and some of the detected schools were immediately sampled with a six-frequency echosounder (Simrad EK60), then trawled with various nets to verify the target species and their size composition. For schools acoustically categorized as euphausiids, data from the two acoustic systems were used to estimate the school morphometrics and the krill size distributions. The principal objectives of this study were to explore the potential of combining data from a multibeam sonar, multifrequency echosounders, and nets, and to describe the efficient processing methods and software that facilitate the multi-instrument analyses. Three-dimensional morphometrics based on the MS70 data were consistent with corresponding two-dimensional morphometrics based on the echosounder data and could be used to improve the acoustic classifications of taxa or species. Additionally, automatic preprocessing and integration of data from different sources into the same user interface allowed efficient exploration and interpretation of all the acoustic data.

SUMMARYA multiblock/multilevel algorithm with local refinement for general two-and three-dimensional fluid flow is presented. The patched-based local refinement procedure is presented in detail and algorithmic implementations are also presented. The multiblock implementation is essentially block-unstructured, i.e. each block having its own local curvilinear co-ordinate system. Refined grid patches can be put anywhere in the computational domain and can extend across block boundaries. To simplify the implementation, while still maintaining sufficient generality, the refinement is restricted to a refinement of the grid successively halving the grid size within a selected patch. The multiblock approach is implemented within the framework of the well-known SIMPLE solution strategy. Computational experiments showing the effect of using the multilevel solution procedure are presented for a sample elliptic problem and a few benchmark problems of computational fluid dynamics (CFD).

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