Multifrequency acoustic assessment of fisheries and plankton resources

Abstract

The range of target species encountered in marine biological resource assessment and the inability to obtain a broad view of these resources by direct physical sampling techniques has lead to the utilization of various indirect measurement techniques. Among these techniques is the use of acoustics (sonar) to determine biomass distribution through echo integration and target strength measurements. WHOI is using a multifrequency acoustic system to obtain more accurate measurements of target species on the Georges Bank. The system uses advanced acoustic techniques (FM slide-encoded pulses) to enhance detectability at the lower trophic levels. An advanced towing technique enables sampling the water column to depths in excess of 200 m. U.S. GLOBEC GEORGES BANK PROGRAM Woods Hole Oceanographic Instituition (WHOI) is a major participant in the U.S. GLOBEC Georges Bank Program. One goal of the program is to understand the population dyamics of key species on Georges Bank including the larval phase of cod and haddock and several species of zooplankton. This requires a broad-scale field survey of the target species. Direct methods, such as physical sampling, while providing an accurate picture of the physical distribution and abundance of the population, are time-consuming, costly, and limited in coverage. To increase the area surveyed, WHOI has been using indirect sampling techniques, including both optical and acoustic solutions. These techniques when combined with limited direct sampling provide an accurate, broad-scale view of populations on Georges Bank.

The Development of SONAR as a Tool in Marine Biological Research in the Twentieth Century

“…Efforts to improve the system led to the use of seven different frequencies, 38 kHz, 43 kHz, 120 kHz, 200 kHz, 420 kHz, 1 MHz, and 2 MHz in BIOMAPER II. This refinement along with the ability to vary the depth of the tow fish depth greatly enhanced the capability of acoustically sampling a wider range of trophic levels including at least some of the primary producers, planktonic algae [50,51].…”