The highlight of our first week of observing the surface and acoustic behavior of marine mammals in Haro Strait during the ship slow-down trial was an encounter with Bigg’s killer whales*. Not only were we lucky enough to observe a foraging event from afar visually within our northern study area, but also the underlying hydrophones recorded an interesting combination of vessel noise and killer whale vocalizations. Here are a couple examples of their relatively rare calls. Our colleague, Dr Volker Deecke, found that Bigg’s killer whales are typically very quiet compared to the relatively chatty southern resident killer whales. Bigg’s killer whales listen for their marine mammal prey and become vocally active only after a successful attack like the one in this video.
We are still learning what impact noise from ships and boats has on Bigg’s killer whales in the Salish Sea.
- Species: Killer whale (Bigg’s ecotype)
- Number: 5 (4-6)
- Vessels present: 1 ship; 4-5 boats
- Location: Orcasound Lab
- Date: Aug 21, 2017 (Monday, day of total eclipse)
- Start time (PDT): 13:20
- End time (PDT): 14:55
- Duration (hh:mm): 01:35
- Observers: Erin Ashe, Laura Bogaard, Laurel Yruretagoyena, and Rob Williams
Overall, the vocalizations were relatively faint and the raw data that Scott reviewed included calls and a few whistles. The recordings contain moderate vessel noise, with boat noise being relatively constant and ship noise levels varying. For context, the soundscape was much noisier before and after this period.
Here are two 5-minute files (mp3 format) that include the time when the Bigg’s killer whales’ changed their surface behavior. An extended (~5 minute) vocal bout bridges between the end of the 13:40 file and the beginning of the 13:46 file.
From the 5-minute recordings, Scott extracted this 90-second clip to showcase the calls types and rate, as well as a whistle. In the spectrogram below you can see that the calls have fundamental frequencies near 1.2-1.8 kHz and harmonics up to ~3 kHz. A whistle at the beginning of this clip varies between 3.5-5.0 kHz and lasts about 8 seconds. At low frequencies (100-200 Hz) there is a power-boat accelerating at 10.5 secs and a possible percussive sound at 14.0 secs.
Zooming in on some of the clearer call sequences in the 90-sec clip, it becomes evident that the duration of these calls ranges between 0.7-2.0 seconds. Most calls last slightly longer than a second.
Here is the resultant 8-second clip, and then single examples of an ascending and a descending call. (All are mono for portability.)
The raw audio files (5-minute, 50 Mb, WAV files) for this encounter can be found in this raw data directory.
All processed data discussed in this post (audio clips, compressed lossy/lossless audio formats, spectrograms, etc) can be found in the processed data directory for 20170821.
* We follow the tradition of many killer whale researchers, who now refer to the transient, mammal-eating killer whale ecotype as Bigg’s killer whales to honor the late Dr Michael Bigg, a pioneer in killer whale research. Avoiding the term “transient” seems especially fitting this summer, because these marine-mammal orcas are the only ones that have been around! The southern resident killer whales have not yet transited Haro Strait (our general study area) during our study.