Sei what?

(This post was originally published September 21, 2021. Posts have been manually reordered for more logical storytelling. To go to the next post in the sequence, click “Previous Post” at bottom.)

We were near the outer edge of the California Current, where the ocean is clear but still tinged green. From our mounted 25-power “bigeye” binoculars, we saw some large blows, 3–4 miles ahead. Several minutes later there was a commotion near where the whales had been blowing: roiling bait, jumping tunas, and a bird flock fluttering overhead.

Arctic terns had finished their breeding in the high arctic and were making their way south to the edge of the Antarctic pack ice, feeding opportunistically along the way to fuel the longest annual migration of any bird (25,000 miles round trip). A flock of 50 or so terns were hovering low over the melee, dropping down to pick off small bait fish that albacore tunas had corralled and driven to the surface. The water was boiling with frantic fry trying to escape the tunas rocketing around beneath them.

A sei whale lunge feeds at the surface; its throat pleats are just beginning to expand as a foraging arctic tern looks on. Photo by Todd Pusser.

Suddenly, a whale lunged into the scene, and a lower jaw, large enough to walk into, swept sideways across the surface and through the dense swarm of fish. These were sei whales (some say “say”; some say “sigh” — say what you will). Rorquals are baleen whales with expandable throat pleats, and the sei whale, at about 60-feet long, is the third largest, behind only the blue and the fin. Rorquals feed by lunging at masses of small prey, and when they open their mouths, their throat pleats balloon out, allowing them to take in tons of prey soup in a single gulp. Then they close their mouth most of the way, and their rebounding throat pleats force the water through the baleen plates and out of their mouth. The prey is filtered out through the sieve formed by their baleen fibers before being swallowed.

The bait fish were too tiny for us to identify from our vessel, but fortunately the crew were trolling fishing lines behind the boat, and when we made a close pass by one of the bait balls, a 23-lb albacore was landed. I reached in its mouth and pulled out a fresh juvenile anchovy, more than 2 inches long. Too small for a pizza, but served up by the ton to the local food chain.

~Robert Pitman

Another sei whale lunge feeds, showing its throat pleats, also known as gular grooves, visibly expanded to take in a huge amount of water — and, hopefully, prey. In this photo by Todd Pusser, the whale is lunge-feeding away from us; its dorsal (upper) surface is to the right and ventral (underside) is at the surface to the left, exposing the left pectoral fin.

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