Erin M. Oleson

Blue Whale (Balaenoptera musculus) Diel Call Patterns Offshore of Southern California

Diel and seasonal calling patterns for blue whales (Balaenoptera musculus) were observed in coastal waters off southern California using seafloormounted autonomous acoustic recording packages (ARPs). Automated call counting from spectrogram cross-correlation showed peak seasonal calling in late summer/early fall. When call counts were organized by daily time intervals, calling peaks were observed during twilight periods, just after sunset and before sunrise. Minimum calling was observed during the day. Nighttime calling was greater than daytime calling, but also showed a minimum between the dusk and dawn calling peaks. These peaks correlate with the vertical migration times of krill, the blue whales’ primary prey. One hypothesis to explain these diel variations is that blue whale calling and foraging may be mutually exclusive activities. Fewer calls are produced during the day while prey are aggregated at depth and foraging is efficient. More calls are produced during the twilight time periods when prey are vertically migrating and at night when prey are dispersed near the sea surface and foraging is less efficient.

Frequency based Algorithm for Robust Contour Extraction of Blue Whale B and D calls

The sea is home to a myriad of marine animal species, many of which use sound as a primary means of communication, navigation and foraging. Of particular interest are the Blue whales (Balaenoptera musculus) of the cetacean family. Massive commercial whaling prior to 1960 brought the species close to extinction and its population still remains very low. Passive acoustic monitoring of baleen whales has recently been used to provide long-term information about their presence and behavior, and provides an attractive complement to traditional visual based monitoring. In this work we present a frequency domain based algorithm developed for extracting the frequency contours of the dominant harmonic in tonal calls of blue whales (B and D calls). The algorithm uses a two pass approach to contour extraction. In the first pass, partial candidate contours are formed, followed by a second pass which uses the partial information to construct complete contours. When evaluated on a one hour labeled recording, the algorithm had 90% recall and 76% precision.

Blue whale B and D call classification using a frequency domain based robust contour extractor

Passive acoustic monitoring of blue whales (Balaenoptera musculus) has been used to gain insight into their presence and behavior. Many of their calls have been shown to be detectable through spectrogram correlation due to the low variation in these stereotyped calls. In this work, we describe rule based classifiers for tonal B and D calls using the pitch/frequency contour information obtained from a contour extractor. B calls can be detected by spectrogram correlation, but the D calls are highly variable and are therefore difficult to detect using spectrogram kernel methods. Experiments on four hours of evaluation data from different field seasons show that 91.3% of B calls and 85.8% of D calls were correctly retrieved. For both types of calls, less than 2% of the retrieved calls were false positives.

Long-term trends in ambient and anthropogenic noise in central and western Pacific Ocean

Multi-year studies of ambient noise trends are uncommon, yet they can provide information on the level of natural variability in noise to which animals are exposed, as well as an idea of changing noise level trends. To investigate long-term trends in low frequency (<1,000 Hz) ocean ambient noise, recordings were collected at two locations in the tropical Pacific Ocean. One site was in the central Pacific, off Kona on the Big Island of Hawaii (2007-2015), and the other in the western Pacific near Saipan, Northern Mariana Islands (2010-2015). In addition, detailed occurrences of two types of transient anthropogenic noise events, vessel passages and mid-frequency active (MFA) sonar transmissions, were identified in a subset of data. Characteristics of those anthropogenic sounds: duration, received levels, and sound exposure levels were measured. Both sites exhibited relatively low levels of ambient noise characteristic of ships (<100 Hz) compared to levels reported in the eastern North Pacific Ocean. At Kona...