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On the water

Posted: October 5, 2012 - 12:01am
A sea lion holds a captured octopus, while a gull waits above in hopes of scraps.  Photo by Tammy Gray Antoniadis
Photo by Tammy Gray Antoniadis
A sea lion holds a captured octopus, while a gull waits above in hopes of scraps.

I don’t get to go whale-watching very often, but when I do, I usually see something interesting and new questions frequently get stirred up.

One trip gave us a good view of humpback whales doing their locally famous bubble-net feeding. Most of us here have seen this behavior at one time or another, but somehow it has not become “old hat.” How does a group of whales decide which one will create the rising, circular curtain of bubbles that rings a school of little fish? How did they invent this foraging tactic in the first place? Did it really originate here, and get carried to Prince William Sound whales by a wandering Juneau whale? How do they coordinate the upward rush of several whales through the panicking fish and avoid crashing into each other?

Another trip brought a troop of Dall’s porpoises, cavorting around the bow of the ship. The group grew, as additional individuals came zooming in from who knows where. They played there for some time, to the great delight of all on board. Then they disappeared, apparently on some magical signal; suddenly they were simply gone, vanished out of sight. Why did they all gather by our ship? And why did they go?

Then, in early September, we watched a small pod of orcas cruise by Little Island, where hundreds of Steller’s sea lions, of all sizes, had hauled out. Even the few sea lions that happened to be in the water a few feet from their dry confreres on the beach did not seem to be alarmed at the orcas passing nearby. Mammal-eating orcas don’t use their sonar to find prey, because mammals can hear the beeps. So we thought that these must be a resident, fish-eating bunch of orcas, using their sonar to find fish and therefore no threat to the sea lions.

As the orcas went on down along Ralston Island, we learned that this was actually a group of transient, mammal-eating predators, identified by a known mark on one of them. Nevertheless, no prey was visible and they acted (to our eyes) as if they were hunting fish: sudden, brief changes of direction and quick dives. This led to the question of whether mammal-eating orcas might sometimes snack on fish as well.

Then a small band of juvenile sea lions came into view from the opposite direction, seemingly oblivious of the jinking-around orcas—until the two groups of animals were very close. Then the sea lions really freaked out, caught between the rocky shore and the orcas. Much frantic splashing and churning about! As the orcas placidly went on their way, the sea lions calmed down and swam toward Little Island. What was going on here? Mammal-eating, transient orcas with already full stomachs? Just fun and games for the orcas? Mistaken identification by the sea lions?

Later that same afternoon, we encountered a scattered group of humpbacks doing nothing very exciting. But alongside our boat there appeared a solitary sea lion with something in its teeth. That sizable something was tossed and thrashed about until it was just a rag (and a few loose bits for the attending gulls). Finally we got a closer look and saw tentacles with sucker discs, just before the whole thing disappeared down the gullet of the sea lion. The octopus was caught at depth of over four hundred feet, not a very deep dive for a sea lion.

• Mary F. Willson is a retired professor of ecology.

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