Title : An acoustic technique for the evaluation of fish behavior in aquaculture pond
Abstract:
Information regarding abundance, growth status and behavior of fish in aquaculture ponds is needed for farmers in conducting proper management practices. Developing proper and reliable methodologies for determining inventory, length distribution, movement behavior and distribution pattern for these mobile objects involves four observational challenges, i.e., detectability, spatial coverage, temporal repetition rate and temporal coverage. An acoustic surveying system, with horizontally orientated and mechanically rotated beams, (i.e., mechanically scanned imaging sonar) under bottom-fixed deployment configuration was adopted to mapping and quantifying the occurrence, status and distribution of fish in aquaculture pond. The current investigation was conducted on a concrete pool of 8 x 6 x1.7m in dimensions where 18 giant groupers (Epinephelus tukula) with current length of about 100cm were stocked for over 10 years. Multiple acoustic image frames collected at this pool, with three consecutive scanning range settings (i.e., 5, 7.5 and 10m), were processed and analyzed. Through visual observation and image intensity threshold procedure for the detection, identification, enumeration and measurement, spatial-temporal information regarding fish objects in this pool were derived, which include position of occurrence, orientation and acoustic trace length. Abundance (17 groupers), averaged length (96.9 cm), swimming speed (30 cm/sec RMS) as well as distribution pattern and movement characteristics of the groupers in this pool at the specific surveying time (lasted for 60 minutes) were derived and quantified thereafter. During this investigation, most of the groupers were distributed at the second and further half of the pool relative to the sonar deployment site and circling around the pool edge with two prominent meeting points. It should be emphasized that these giant groupers were able to detect the existence of the acoustic pulses from the sonar system and tried to avoid them actively. It is, therefore, concluded that the integrating of the proposed acoustic apparatus, deployment configuration and image processing procedures for the acquisition of spatial-temporal characteristics of fish species represents a potential candidate for the resolving of inventory and related problems in aquaculture for both fish as well as shrimp.
