MARINE MAMMAL RESEARCH NEWSLETTER  |  September 2015 (Issue 13)

Crunching the Numbers

Decoding the mysterious songs of fin whales

Loud, deep, mysterious pulses of underwater sound were first recorded in the early 1950s, but the source remained a mystery for decades. Scientists investigated and ruled out seismic activity, wave action, barometric pressure fluctuations, major weather events, land based machinery, pile driving, power generators, planes flying overhead, and the jet propulsion of giant squid. They noted the strange pulsed sounds had extremely regular timings, arranged in a doublet pattern of alternating long and short time intervals. Some likened the pattern and its regularity to the rhythm of the human heartbeat, and prompted the hypothesis that the pulses were the sounds of the beating hearts of large whales.

 

Figure 1

Fin whales are the second biggest species of whale. They occur in all the major oceans except the coldest regions where ice prevents traveling and surfacing.

The loud pulses were in fact the vocalizations of fin whales, and the consistent doublet pattern was the stereotyped fin whale song pattern. Male fin whales produce these monotonic pulses almost year-round, particularly during the winter breeding season when they are arranged into patterned songs.

Figure 2: pulses

A spectrogram of 20-Hz fin whale notes recorded near Brooks Peninsula.

In a collaborative study with Fisheries and Oceans Canada and JASCO Applied Sciences, MSc student Barbara Koot analyzed the calls of fin whales recorded on underwater hydrophones deployed along the BC coast to gain insights into the movement patterns and population structure of fin whales inhabiting the North Pacific.

figure 3: BC map

Locations of hydrophones that recorded fin whale calls. The color circles indicate where song type 1 (red) and song type 2 (blue) were detected. Note that both song types were recorded at the Bowie Seamount and near Langara Island.

Although once thought to be just summertime visitors, Barb found some fin whales remain in BC waters throughout winter to mate and possibly feed (based on the timing and frequency of their calls). She also discovered that fin whales produce two different songs in BC that appear to belong to two spatially segregated populations of fin whales—one that is coastal and one that is further from shore and may belong to the Southern Hemisphere subspecies.

Figure 4:

Visual and acoustic observations of fin whales at high latitudes in the winter suggest that the movement patterns of fin whales may be more complex than other species of baleen whales.

Barb’s results show that BC waters are important for fin whales year-round, rather than just during the summer feeding season―and that more than one population likely uses these waters. Her findings have significant implications for fin whale conservation and management strategies.

Barbara Koot completed her MSc degree at the University of British Columbia, and will be presenting her findings at the upcoming Biennial Conference on the Biology of Marine Mammals in San Francisco.

 


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