This summer the BC Cetacean Sightings Network is spending some time in the field on the central coast of BC. Covering the area between Port Hardy and Bella Bella aboard the Vancouver Aquarium’s research vessel M/V ‘Skana’, the BCCSN hopes to create new relationships with potential observers and survey the coast to help assess cetacean abundance. The ‘From the Field’ series of news posts will highlight some of the discoveries and encounters along the way.
From the field #3: Listening for whales
Fog. Not what you want to see when you wake up in the morning on a cetacean survey. Not only does it make navigation difficult and more dangerous, but finding whales also becomes much harder! Even on clear days, a set of binoculars can only see so far. So while out in the field, whales are sometimes found not with our eyes, but with our ears.
To eavesdrop on the underwater world, researchers (and curious whale enthusiasts) use a hydrophone, essentially an underwater microphone that hooks up to a sound system. The hydrophone allows listeners to detect highly vocal species, such as resident killer whales and Pacific white-sided dolphins, which emit sound within the range of human hearing. Depending on the underwater geography of the area, hydrophones can often pick up vocalizations over 10km away.
After a week on the ‘Skana’ of not hearing a peep (except for passing boat motors) on the hydrophone, we finally got lucky! While sitting in the surprisingly calm waters near Goose Bank (off the central coast), with no land in sight and nothing between us and the southern tip of Haida Gwaii, over the speakers came a distant squeak: Killer whales!
Excitedly, we attempted to figure out from which direction the sound was coming from. To get a good scope of the underwater world, the hydrophone collects sound from 360’. However, if the whales are still out of visual range, a few adjustments of the hydrophone with a home-made shield allow us to determine which direction the sound is coming from. Have a listen to what we heard:
Toothed cetaceans like killer whales make these sounds by pushing air through nasal sacs just inside the blowhole. These nasal sacs have a set of phonic ‘lips’ in which air is squeezed through to make various clicks, chirps and whistles. To get a rough idea of how this works, imagine blowing up a balloon and then pinching the opening while letting out the air. For toothed cetaceans, that sound generated is then focused out through their ‘melon’; the fatty sac that sits on top of their skull. This melon acts as an acoustic lens, broadcasting the sound forward into the underwater environment, and sometimes right towards the hydrophone!
Even before we saw these whales, we could tell they were ‘northern resident’ killer whales. ‘Residents’ are the eco-type of killer whales that feed on fish, particularly salmon. As many fish species do not rely heavily on their hearing, it is not a very well developed sense for them. Therefore resident killer whales can vocalize often (and loudly!) without having to worry that their calls will scare off their prey. The calls made by resident killer whales play an important role in keeping groups together and cementing social bonds. They live in stable family groups, where neither male nor female offspring leave their mothers. As such, distinct dialects arise in groups, to the point that researchers can identify whales exclusively by the sounds they hear. Check out calls of different clans here.
On board the Skana, we had narrowed down the area in which the sounds were coming from and started scanning the horizon in that direction. Pretty soon the ‘puff’ of blows was heard, and then the distinctive black fins appeared in the distance. It was resident killer whales indeed, a large group of many different families! It was time to put the hydrophone away and start using our eyes (and cameras!) to identify individuals. Thanks to the hydrophone we had an exciting encounter ahead of us.