Orcas head north & south for Salish Sea salmon

Today (9/27/2020) at least two pods of the endangered Southern Resident Killer Whales (SRKW) came into the Salish Sea from the Pacific Ocean. As autumn begins, many of us were wondering if they would go north towards the big Chinook of the Fraser River in BC as they often do during the summer, or south into Puget Sound for a first pursuit of coho or fall chum salmon runs…

Under the watchful eyes of whale watchers like the Western Prince II, K pod worked their way from the Port Angeles/Dungeness spit northwards along the west side of Hein Bank. They proceeded up into Haro Strait and were observed by the sighting network on land along the west side of San Juan Island as the sun set. Later that evening, at 21:05 standing on the bluff above the Orcasound Lab hydrophone location, Val Veirs reported “9:05 breaths in the dark. No vocals on hydrophone.” Listeners monitoring that hydrophone via live.orcasound.net/orcasound-lab may have heard a faint call or two, but the lack of calls implies that K pod may have been resting as they moved northward against the ebb.

Based on the Kellett Bluff current model, the tide was ebbing as K pod moved north through Haro Strait (9/27 ~17:00-23:00).

Interestingly, instead of hearing the expected K pod calls, multiple human listeners including Alisa and I heard some surface splashing and endearing squeaks. We concluded that this must have been a river otter or two frolicking in the moonlight just above the Orcasound Lab hydrophone (which is relatively shallow at a depth of about 8m below MLLW).

At about the same time, I was randomly checking the other Orcasound hydrophones — at Port Townsend and Bush Point — near the entrance to Puget Sound proper. Around 20:35 I convinced myself that I was hearing extremely faint calls on the Bush Point hydrophone that had just been fixed by Lon Brocklehurst in partnership with the hosts of that location, Susan and Howie of Orca Network. I was only about 70% sure I was hearing SRKW calls, so sent this (most convincing, but not very compelling!) clip to Orca Network and Val for a “sanity check” and kept my attention on the known location of K pod further north.

1 minute clip – .ogg format
1 minute clip – .mp3 format

Meanwhile a series of slow-moving tugs and a vehicle carrier emitting intense noise near Bush Point made it nearly impossible for anyone to verify what I thought I’d heard! Nevertheless, the SRKWs must have moved closer, because occasionally a recognizable call was audible to Susan, Howie, and Alisa — even over such intense masking noise. This spectrogram of the 6-hour recording (from ~17:30-23:30 Pacific time) shows that about half the time the whales in Admiralty Inlet were awash in noise from passing ships and the ferry run from Port Townsend to Coupeville (audible at Bush Point, despite being some 14 km away).

6-hour spectrogram from Bush Point with a ~2-hour period of ship noise highlighted (in blue/green). I heard faint calls just beforehand (when the whales were likely southbound between Bush Point and Port Townsend). The “concert” began right afterwards…

Finally, the southbound vehicle carrier cleared Bush Point, the cacophony subsided, and we were treated to this “orca concert” as the whales moved south into Puget Sound proper for the first time in fall, 2020:

38-minute “concert” by J pod — .ogg format
38-minute “concert” by J pod — .mp3 format
38-minute recording with “best” ~12-minute highlighted (blue/green)

The 38 minute clip from about 10:30-11:15 p.m. Pacific time (start at: 17:30:21+05:06:01=22:36:27; end at 22:36:27+00:38:02=23:14:29). There are two periods I’d like to highlight. The first is the minute section where the ship noise fades out suddenly, illustrating the relative intensity of the noise and the signals of the nearby SRKWs. The second is about 12 minutes between when the ship noise suddenly abates (blocked by the Bush Point bathymetry, I suspect) and the ship wake arrives at the shoreline and generates a bunch of flow noise. This is the “highlight” of the concert — when the orca call signals were well above the ambient noise in Admiralty Inlet.

Here is a clip of the ship noise fading and the SRKWs becoming more audible from the perspective of the hydrophone —

2-min ship noise fading to orca calls — .ogg format
2-min ship noise fading to orca calls — .mp3 format
spectrogram context for the 2-min clip showing transition from vehicle carrier ship noise to J pod calling in typical “urban ambient” background noise.

Listening to this is one way of intuiting how much ship noise decreases the active space of orcas — both for echolocation and communication signals.

And here is a clip with the best SRKW signal:noise ratio —

best 1-minute — .ogg
best 1-minute — .mp3

It has a couple of great whistles, and many repeated, sometimes overlapping calls. The calls are most similar to S1s (commonly made by J pod), but are also sort-of a mash-up of S3s and S7s. There’s a couple S4s at the end for fun.

Take a listen to this 2020 version of the SRKW call catalog and comment on what you hear! There are some great “excitement calls” (S10 for SRKWs) in the 38-minute clip. There is also a really funny call near 9:44 (that I think sounds like a teenager orca’s expletive). Can you find them?

Here’s a spectrogram of the ~9-minute section when the hydrophone was getting buffeted by the ship wake. Let’s not forget that this high-energy event was experienced by inter- and sub-tidal creatures, all up and down Puget Sound! Avoiding this turbulent disruption 10s of times per day is yet another reason to get ships to slow down in Puget Sound…

Pulses of flow noise from a the vehicle carrier wake breaking along the Bush Point shoreline lasted almost 9 minutes. (Such measurements are a benefit of very shallow deployments in Puget Sound, as is occasionally hearing birds at low tide…)

Luckily the “concert” ended as the killer whale calls grew progressively fainter, rather than being interrupted. In the final minutes, the background noise was low enough that you could hear the reverberation of the more intense calls, especially during a series of repeated calls.

Finally, the currents shifted and the Bush Point hydrophone began to flutter in the flow, generating a lot of low-frequency noise. There are some exciting eddies and counter-currents that spin off of Bush Point (just ask Florian who has dived there extensively!)… and I wonder if both K pod in Haro and J pod in Admiralty While this flow noise made it hard to listen to the final fading calls of the orcas, it also inspired me wonder if we could estimate the current speed from the intensity of the fluttering… Even during Covid our scientific cups can still be seen to be at least half full.

Tidal currents near Bush Point 9/27/20
Source: http://www.dairiki.org/tides/daily.php/adm/2020-09-27

Note:

  • You can download the .ogg and .mp3 clips using the “3 dots” on the right side of the HTML5 audio player
  • S3 bucket with raw data from this event has Unix timestamp: 1601253021
  • Geeky guidance for open access to Orcasound data via AWS CLI
  • If you’re a budding marine bioacoustician and would like to co/author blog posts like this, just let us know and we’ll set you up with a WordPress account!

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