Characteristics of the deep scattering layer in the Gulf of Mexico as they relate to sperm whale diving and foraging behavior

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Title: Characteristics of the deep scattering layer in the Gulf of Mexico as they relate to sperm whale diving and foraging behavior
Author: Azzara, Alyson Julie
Abstract: This research was carried out in support of fieldwork in the Gulf of Mexico in summers 2004 and 2005 as part of the multidisciplinary Sperm Whale Seismic Study (SWSS ) . Important aspects of SWSS research include oceanographic habitat characterization and studies of sperm whale foraging and diving patterns . During the SWSS 2005 cruise , acoustic volume backscatter data were collected using a 38 kHz ADCP for comparison with XBT , MODIS ocean color data , and whale dive profiles extrapolated from analysis of towed passive acoustic hydrophone array recordings of whale vocalizations . This unique data set , collected from a cyclonic eddy , was compared with non -upwelling conditions surveyed in the western Gulf and the Mississippi Canyon in summer 2004 . My focus was to examine the relationship between acoustic backscatter intensity from the deep scattering layer (DSL ; usually 400 -600 m deep ) and the depths to which whales dived . The results of the study investigate differences in DSL characteristics between divergent zones and non -divergent zones , and examine connections relating to variations in sperm whale dive patterns . The analysis of 38 kHz ADCP data showed that there were significant differences in some characteristics of the main DSL dependent on time of day . There were no significant differences in characteristics of the main DSL between divergent and non -divergent areas or between 2004 and 2005 . The comparison of the 38 kHz ADCP and the 70 kHz Simrad echosounder data yielded a relationship of 4 ADCP counts for every 1 dB of Sv . This relationship was a promising start to a potential calibration for the ADCP instrument . Lastly , the analysis of localized sperm whale dive profiles identified three basic dive profiles ; Deep ( > 800 m ) , Mid -water dives to DSL depths (500 - 800 m ) and Shallow ( <500 m ) . The analysis also showed that whale dive behavior did not change based on time of day or location . It showed that whales are diving above the DSL as well as through and below , however these dives are independent of differences in DSL characteristics .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1173
Date: 2009-05-15

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Characteristics of the deep scattering layer in the Gulf of Mexico as they relate to sperm whale diving and foraging behavior. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1173 .

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