Part of research is, of course, figuring out what other people in my field have done, and are doing. Today I was looking up how other people have been looking for fin and blue whales acoustically. It turns out that the Bioacoustics Research Program within the Cornell Lab of Ornithology is a good place to start. Don’t be fooled by their name – they’re not just looking at birds. The research overview portion of their website describes research that they do on elephants and whales, too.
One of their areas of research is in looking at low frequency whale calls using the SOSUS network. SOSUS stands for SOund SUrveillance System, and was used during the Cold War to monitor submarines and surface vessels. SOSUS is part of the larger IUSS network (Integrated Undersea Surveillance System). The US Navy has been working with Bioacoustics researchers at Cornell University to look for whales since 1993.
Here’s an example from their website, showing different types of whale calls that they see. They’re displayed as spectrograms, where the x-axis is time, and the y-axis is frequency.
Because of the sample rate of the seismometers in the KECK network, the data I’m working with are limited to 64 Hz. The data shown above includes minke and humpback whales, which are in the range of 100-300 Hz. Low compared to, say, a multibeam sonar, but much higher than what I can see in my data.
Several of the researchers at BRP went down to the Sea of Cortez to listen to fin whales, and to try to understand how human-made underwater sound affects whales. Using a variety of methods – not only acoustic – they observed that only the male whales were vocalizing. Here’s the one-sentence summary from their website:
This results of this research suggest that the long, low-frequency songs of male fin whales function to attract females to dense patches of food, where mating then occurs.
This is interesting. Why is it only the males that sing? And why do they attract females to patches of food to mate? I’ll have to read up on this…