Graduate Thesis Or Dissertation
 

Sound scattering by marine organisms in the northeastern Pacific Ocean

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  • Sound scattering by marine organisms was studied off the Oregon coast and between Hawaii and Adak, Alaska. Variations in scattering were observed over a period of several hours, over did (24-hour) periods, from month to month, from inshore to offshore, in relation to biomass of midwater animals, and temperature and salinity. Usually one or two scattering layers migrated vertically, ascending or descending at dusk and dawn respectively. At times reflectors migrated between surface waters and upper scattering layers during twilight periods. No statistical difference was found between rates of ascent and descent because of the variability in rates of migration that was observed. The amount or thickness of scattering in the water column was found to vary from day to night and with seasons. There was a general trend for more scattering during night than day, yet it was not statistically significant. Seasonally, more scattering appeared to be present during the summer in some years but not in others. Surface scattering varied not in amount but in the type present during different seasons and between day and night. Geographically, scattering was found in smaller amounts in offshore than inshore waters of Oregon. Variations in scattering were noted among the water masses between Hawaii and Adak, Alaska. Geographic changes in scattering and biomass showed a positive correlation between euphausiid catches and the amount of scattering. However, euphausiids are not considered the only group scattering sound. The great amount of variability in scattering is discussed. It may be due to differences in the species causing scattering and variability in the behavior of individual species, possibly resulting from changes in light and temperature.
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