Bioacoustic Absorption Spectroscopy

Abstract

LONG TERM GOALDemonstrate the potential of bioacoustic absorption spectroscopy for tomographic mapping of the bioacoustic parameters of fish with swim bladders in shallow water. OBJECTIVESDevelop an acoustic propagation model that accounts for bioacoustic absorptivity due to fish with swim bladders on transmission loss as a function of frequency over the frequency range 0.5-5.0 kHz in shallow water. Develop a bioacoustic model that accounts for the resonance frequencies of absorption lines, which are due to dispersed pelagic fish, and schools of pelagic fish with swim bladders. Develop a model of the seasonal variability of resonance frequencies. Demonstrate consistency between absorptivity and echo sounder based estimates of number densities. APPROACHInvert bioacoustic parameters from transmission loss data recorded during Modal Lion, by matching theoretical computations with data. Demonstrate consistency between absorptivity and echo sounder based estimates of number densities of sardines in the Gulf of Lion. Develop an analytical model to account for the frequencies of measured absorption lines by extending a previously published theory of the resonance frequency of "bubble clouds". Design broadband, long term, autonomous sources and receivers, that will permit long term monitoring of bioacoustic parameters. Conduct new bioacoustic absorptivity experiments in littoral seas in co-operation with fisheries biologists. The first planned experiment will be in the seas off California in co-operation with the Southwest Fisheries Science Center of NOAA's National Marine Fisheries Service. These experiments will be designed to investigate the "signatures" of the two major classes of fish with swim bladders physotomes (volumes vary inversely with pressure) and physoclists (volumes are independent of pressure) in time frequency space. Simulate effects of absorptivity on transmission loss vs. time and frequency of physostomes and physoclists. Apply model to new and previously published bioacoustic absorptivity measurements, derive bioacoustic parameters, and demonstrate consistency with biological measurements.