Local Harbor Seals Apparently Know That Resident Orcas Don’t Eat Them

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It is an amazing concept, but apparently true: harbor seals can tell the difference between the type of orcas that hunt them (called “Transients”) and the Resident fish-eating orcas which don’t. The seals behave differently around the two types of orcas, which is something I recently noticed – and I have also heard similar tales of a minke whale that has been seen swimming among the J and L pods this summer, another example of an animal that seems to know the difference between the two orca types.

Right now is the height of seal pupping season over much of the range of harbor seals in the Salish Sea, and the baby seals are occasionally picked up by well-meaning individuals who think the pups are lost. Normally however, the mother seal is nearby foraging, or may have been frightened by the approach of humans and is swimming with a careful eye on her pup. (The standard advice is to retreat at least 100 yards, and to call the authorities if you really think the pup is hurt or lost – to report a marine mammal strandings and violations call the NOAA Hotline: 1-800-853-1964).

This alert mother spotted a harbor seal pup among the rocks, then quietly withdrew with her son.

My own recent encounter with a mother seal and her pup started the same way, but because I was watching orcas feeding nearby, I grew very curious about the predicament that seemed to face the mother seal. She had left the pup tucked behind rocks in the rocky intertidal area which, while not remote, doesn’t get many human visitors. There were just two of us there climbing around on the boulders to get a good view of the orcas, and neither one of us knew the pup was there until the other person and her young son started to work their way back from the water’s edge.

Left undisturbed, the baby seal’s coloration helps conceal them from predators.
Shortly after birth the pups can appear thin and neglected.

Once she spotted the baby seal, we retreated up to the low bank that overlooked the rocks where I continued to watch the orcas feeding in the tide rip zone. Some time later, loud splashing in the kelp bed below caught my attention, and there, seemingly oblivious to the presence of the orcas was a harbor seal. It would surface, splash and slap the water for a few seconds, then disappear into the kelp for several minutes. My assumption is that it was the mother harbor seal, and she was foraging for the schooling fish that are abundant there at this time.

The mother harbor seal was swimming nearby in the kelp.
The orcas were just beyond the kelp, by the whale watch boats.

The nearby orcas were also noisily splashing and lobbing the water, and usually are quite vocal too because they often “converse” and echolocate – and given the way sound travels underwater, hard to miss. The kelp would have offered the mother seal some protection had she been making any effort whatsoever to be quiet…but she wasn’t.

Just a few weeks earlier I had watched a young Steller sea lion behave as you would expect in the presence of orcas – he lurked in the kelp bed until the Resident fish-eating orcas left, then swam off with caution. In other words, the Steller sea lion behaved exactly as you would expect a prey species to behave – avoid orcas at all cost and don’t stop to wonder if it intends to eat you or not. So what could explain the seemingly odd behavior of the mother seal? Or the young minke whale that has been reported to hang out with J and L pod orcas this summer, for that matter?

Research on harbor seal foraging and communication strategies offered little in the way of explanation, and a general ‘orcas harbor seals’ search turned up what you would expect in terms of predation and diet etc. Not thinking I would find anything, I finally googled ‘resident orcas harbor seals’ and found both an affirmation and explanation of what I had witnessed – and to me, the implications of this research are fairly profound.

In a nutshell, the researchers tested the effect of Resident versus Transient orca calls on harbor seals, and found that indeed, the harbor seals only responded to the Transients’ calls. The scientists explain that because the Resident orcas are present for long periods of time it is to the seal’s advantage to sort out which orcas represent danger, otherwise they would not be able to spend enough time foraging to sustain themselves, let alone produce the caloric requirement to nourish a pup.
Selective habituation shapes acoustic predator recognition in harbour seals

Harbour seals are the most commonly taken prey of transient
killer whales in the coastal waters of British Columbia, Canada, and
predation from transients is likely to be a significant source of
mortality. Because harbour seals have good underwater hearing at
the frequencies of killer whale vocal communication, and because
underwater calls of killer whales can be heard over long distances,
it would be beneficial for harbour seals to respond to the calls of
transients with anti-predator behaviour. When the salmon migrate
through these waters, groups of resident killer whales, which pose
no predatory threat to seals, will often spend several weeks in a
relatively small area. Seals would therefore waste time and energy if
they responded to all killer whale calls indiscriminately. However,
given the complexity of killer whale vocal communication,
especially of the resident dialect system, consistent discrimination
between calls of the two forms represents a formidable learning task.

…Having a learned component to predator recognition is advantageous
in situations where the nature of the predatory threat is to
some degree unpredictable, or where cues associated with the
predator are highly variable or change with time. Animals that
adjust their predator image by associative learning start out with
one that is too specific and expand it by adding cues (either when
attacked after sensing the cue, or by seeing conspecifics respond to
it) to reflect the actual predators present. This is risky, as it requires
experience with the predators. In contrast, selective habituation
predicts that prey animals start out with a rather general predator
image from which certain harmless cues are removed by habituation.
This initially generates costs from false alarms but not from
missed detections. It does not require experience with the predator,
since any unusual cue that falls within a certain predator class elicits
a response. By selective habituation (learning what not to fear)
harbour seals pursue the more conservative, and thus more advantageous,

No doubt the young minke whale has gotten it sorted out as well since at least some minke whales tend to be more residential in the waters around the San Juan Islands – like harbor seals, they don’t really migrate. Steller sea lions are migratory though, and so may not have the opportunity to learn which orcas present danger to themselves. And once, years ago, I watched a harbor seal seem to fly out of the kelp bed near Lime Kiln Lighthouse on San Juan Island when the Resident orcas swam into the kelp. My guess is that harbor seals may know that they are relatively safe from Transient orcas when the Resident orcas are present (the two types never mix, and the Resident orcas have been observed to chase away the Transients) but when the orcas get too close or too quiet the seals get out of the way.

What all this underscores is that underwater sound is of profound significance, and not just to the whales that need to communicate long distances. While our world is filled with light, and sound plays a supporting role, the world of the ocean is filled with sound and vision is of secondary importance.

When the whales are communicating, many animals are listening in on the conversation, and the sound pollution created by human activity may be causing damage in ways we have yet to explore.

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