Even from a distance the orcas’ exuberance was unmistakable, the splashes created as they breached and cartwheeled out of the water were bright against the gray/blue backdrop of Haro Strait (off the west side of Washington’s San Juan Island).
Whale after whale jumped, leaped, spun, cartwheeled and did flips, and two came up in near perfect unison, side by side in a double breach. Even the calves were participating, their often incomplete breaches amusing to watch.
But the real surprise appeared in the form of several small dorsal fins cutting through the melee; dolphins were swimming among the orcas.
From shore it was impossible to see what kind of dolphins were involved or how close they really were to the orcas, or to get a handle on what the ruckus was all about. Thankfully though, several whale watch boats were out closer to the action and later reported the scene in their blogs.
In his email blog Captain Jim (of Maya’s Westside Charters), identified the dolphins as Pacific white-sided dolphins (often called ‘Lags’, an abbreviated version of their scientific name) and generously shared his photos. He noted how rarely these dolphins have been seen in the inland waters of the Salish Sea, and commented on how the dolphins seemed to be playing with or harassing the orcas – behavior he has also witnessed in the past from the more locally common Dall’s porpoises.
As if on cue, a few days later he encountered the tiny Dall’s porpoises cavorting around the orcas.
These particular orcas, the Southern Residents (given that name because they live in the southern part of the Salish Sea through much of the spring, summer, and fall) don’t eat dolphins, they primarily eat fish. They never consume other marine mammals…but to the untrained human eye they look just like the orcas (called ‘Transients’) that do dine on dolphins and seals. Can dolphins tell the difference? If not, why would they risk making what could turn out to be a really bad choice?
We know that harbor seals can tell the two types of orcas apart by the different sounds the two types of whales make – and the seals adjust their behavior accordingly (see previous post). The theory is that since the harbor seals inhabit the same area all year, they can’t afford to leave the water or hide in the kelp every time they hear an orca, and because the Transients tend to hunt silently, the seals really have to rely more heavily on visual cues.
Unlike the harbor seals, these dolphins are not known to come into the area often, hence would not be expected to discern the calls of the two types of orcas. According to Rain Coast Research, the presence of Pacific white-sided dolphins in this region is tied to the periodic influx of certain forage fishes (mostly smelt and capelin), and the dolphins just have not been in the area often since the early 1900’s. So if the dolphins have learned the difference between Resident and Transient orcas, logically they would have had to do so out in the ocean, or perhaps this knowledge is passed down from generation to generation.
In general, researchers believe that different species, such as the dolphins and the orcas, aggregate together most often when finding food or avoiding predators:
Mixed Species Groups in Mammals
“Mixed species groups have long been noted in birds, but they also occur among different species of mammals ranging from closely related species to species from different orders. Mixed species groups of mammals occur in many different habitats, e.g. ungulates on the savannah, primates in various types of forests and cetaceans in the oceans.
Mixed species groups are very different in their duration, frequency, predominant activity and structure depending on the species interacting and the habitat they occur in.
Functional explanations for mixed species groups usually fall within two categories: foraging advantages and predator avoidance. However, there could also be other social and reproductive advantages of mixed species groups that could contribute to their formation and stability. The advantages do not have to be equally distributed between the participating species and can also vary according to season and the presence of predators.”
Logical enough, but what explains the crazy looking kamikaze behavior of the dolphins as they swim over and around the orcas?
If the association was based on predator avoidance, it implies that there was something even scarier around; think Jaws, or Transient dolphin-eating orcas. Even so, why would the dolphins appear to harass their presumed protectors?
A better guess is that this behavior is somehow related to foraging, and either the dolphins located the orcas feeding on fish (sea lions have been demonstrated to follow dolphins, presumably because of the dolphins’ superior ability to locate fish schools California Sea Lions Use Dolphins to Locate Food) or, more likely, given the behavior of the dolphins, they might have been harassing the orcas to try to get them to change direction or leave the area, and therefore, the fish, behind – even though orcas prefer larger salmon, there are often smaller forage fishes present as well.
The Pacific white-sided dolphin is a fast and free-ranging species that often approaches boats:
It is also possible that the more free-ranging dolphins and porpoises can’t identify which orcas might eat them, and like crows mobbing an owl they are just trying to drive the orcas out of the area to protect young or injured individuals- but even the little I have seen of the Transient orcas tells me that it would be ineffective and somewhat suicidal for a dolphin to approach them. Not surprising: I found no reports of them having done so.
Behavioral theory does allow for the possibility that the dolphins can quickly learn the difference between types of orcas however, even with no prior experience:
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, strategy. (Previous post).
As an example, the dolphins might have a predator image of a shark, then learn the difference between that and an orca, and finally between the different types of orcas.
But from their end, why do the Resident orcas put up with the frisky dolphins and porpoises? Is it possible that these peaceful, fish-eating orcas actually enjoy the presence of their smaller cousins? Maybe it takes more energy than it is worth to drive them off, or they know that the dolphins and porpoises will soon lose interest and take off on their own. Possibly the orcas do get annoyed and change their direction of travel – just think for a minute what the presence of a tiny bee can do to your own choices. Or maybe the orcas’ nature is just gentle and easygoing. Of course we can’t really see what is going on underwater at those times, and unless we happen to have a hydrophone in the water we can’t hear it either. It is a mystery.
In the final analysis, there are more questions than there are answers at this point, and given the level of intelligence these animals possess, they may relate in ways we have not even begun to explore. Studies all over the world are turning our notions upside down – for instance researchers have discovered that tooth rake marks on some species of dolphins are sometimes caused by interactions with a different, and perhaps more aggressive species, and are not solely a result of conspecific rivalry, as was the long-held assumption.
There is always the possibility that it could just be plain old fun for them all at times, though scientists shy away from applying such concepts to animals. Known to ride the bow waves of the great whales as well as the bow waves of boats, sometimes dolphins will hitch a ride in the direction they were headed anyway…yet other times they seem to go out of their way to cavort in the waves.
No matter how or why they do it, the dolphins seem to have figured out that like us, they are safe around the gentle Southern Resident orcas.