When I first started learning about fin whales, I found it really hard to believe that we (humans, scientists, animal lovers, etc.) still don’t really know where they hung out. What their migration patterns are. If they even migrate! As you know, these animals are enormous. The second largest in the world. How can we not know everything there is to know about the second largest animal in the world??
Well, the answer is pretty straightforward, actually. Firstly, they spend most of their time underwater. Where we can’t see them. Second, the move fast – did you know their nickname is the “greyhound of the sea” – they swim at speeds in excess of 20 knots! It just boils down to the fact that they are really tough to observe for long periods of time.
This is a problem for us – humans did, after all, basically cause the severe endangerment of most large whale species, including fin whales. And now that commercial whaling has been banned, we want to be able to protect them from further harm arising from human activities. Large baleen whales are still at risk from ship strikes, low frequency noise (from ships or active seismic experiments), and entanglement in fishing gear. If we want to protect them, it’s important that we have an idea of where they are in the ocean at any given time.
Probably the most common method that scientist use to assess fin whale distributions is by using visual surveys. This is a whole topic unto itself, a very interesting one, but I’m going to jump past it fairly quickly in this post. Suffice to say that visual surveys are hampered by a couple of things: they are restricted by weather conditions, you can only see whales at the surface, and in order to conduct a thorough survey, it can become very expensive.
Enter, acoustics! (as if you didn’t know that was coming)
Passive acoustic monitoring (PAM) is popular because you don’t have to bother the animals, you can record continuously for weeks or months, maybe even years. You don’t need to worry about weather. Some things you *do* need to worry about: how often do they call? Which animals are calling? Is it only males producing calls as a breeding display? Does calling activity increase near increased food sources?
Up until this point, I had been focusing on a little dataset up on the Endeavour segment of the Juan de Fuca ridge. A teensy little dataset consisting of 8 instruments, each collecting 128 samples per second continuously for three years (that was sarcasm, it’s a ridiculously large dataset). This little dataset (see a bit more here) has been great – I have used it to develop a couple of automatic detectors, and also to measure source levels. But there’s a new dataset on the horizon – the Cascadia Experiment (dun dun!!). This dataset consists of 70 OBSs, spanning the entire length and width of the Juan de Fuca plate, from Vancouver Island to Cape Mendocino, and out to the boundary with the Pacific plate. As far as I know, it is the largest offshore seismic network ever deployed by the United States. The image below shows a map of the coverage.
I’ll try to post some more blog posts discussing a few more details about how we plan on using this dataset to learn about what fin whales are doing – more specifically, what controls fin whale distributions in this area – is it food sources? Is it water depth? Is it related to specific breeding or calving areas? Hopefully we’ll be able to answer some of these questions!