Graduate Thesis Or Dissertation
 

Light and the behavior of pelagic animals during night and crepuscular periods

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/k643b5644

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  • Light plays an important role in ecological processes in the ocean both day and night. While relatively inexpensive, off the shelf instruments are available to measure Photosynthetically Active Radiation or PAR during the day, efforts to quantify light levels at night have proven more difficult. The goal of this work was to quantify nighttime light levels while simultaneously examining the movement of pelagic animals to explore correlations between light levels and the vertical movement of these animals during crepuscular periods and during the rise and set of the moon. This study explores two hypotheses about the role of light with respect to the vertical migration of animals in water. The first is that at a constant depth, light levels correlate with the scattering volume, or abundance, of animals in the water column. The experiment failed to prove this hypothesis; therefore, it is concluded that light is not a significant predictor of the amount of animal scattering volume at a constant depth. The second hypothesis tested is that pelagic animals follow an isolume up and down the water column as light levels change. Experiments showed a wide variance in animal scattering volume along an isolume instead of being relatively constant as would be expected if animals followed an isolume. Additional analysis showed no relationship between volume backscatter and depth. Therefore it is concluded that animals do not follow an isolume up and down the water column as light levels vary. The development of methods to monitor nocturnal behavior of pelagic animals has implications for marine resource management. This study was performed in the Monterey Bay National Marine Sanctuary and provides previously unavailable data to Sanctuary Managers about important nocturnal marine processes. Sanctuary Managers are mandated to use Ecosystem-Based Management principles in managing the Sanctuary. This is a complex marine ecosystem in which the interaction of small scale components can have large influences in macrosystem dynamics which can feed back to influence smaller scale systems again. To assist them, Sanctuary Managers have developed Resource Preservation and Research plans that require data of many types. Experiments incorporating techniques using acoustical instruments to measure abundance and migration patterns of pelagic animals can help Sanctuary Managers better understand the complex linkages of the marine ecosystem in the Monterey Bay National Marine Sanctuary.
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