Azzara, Alyson Julie (2006-12). Characteristics of the deep scattering layer in the Gulf of Mexico as they relate to sperm whale diving and foraging behavior. Master's Thesis. Thesis uri icon

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.
  • 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.

publication date

  • December 2006