Eavesdropping on whales using land seismometers

In a newly published study in Seismica, researchers used instruments on land designed to monitor earthquakes (seismometers) to detect the presence of fin and blue whale calls in the Gulf of St Lawrence.  

What is a seismometer? 

Seismometers are instruments that measure the ground motion and are typically used to study earthquakes. However, they can also record other types of low-frequency noise, including levels below the human hearing range. Examples include noise of geological (volcanic, ice-breaking),  biological (some whale calls), and anthropogenic (cargo trains, ship propellers) origins. 

Monitoring whales using seismometers 

The concept of using seismometers to monitor whales is not new. In fact, whales rely heavily on sound for communication and navigation, producing a variety of vocalizations. Scientists worldwide have tapped into networks of seismometers on the ocean floor to study the calls of species like fin whales and blue whales.

These species are chosen because they produce very loud, low-pitched vocalizations—think of the deep tones of an upright bass in an orchestra. Since lower-pitched sounds travel farther in water, as they experience less energy loss, fin and blue whale calls can cover vast distances. Furthermore, these calls are readily identifiable in datasets because they are repeated in sequences with fairly consistent intervals between “notes.” These unique characteristics make their signals more likely to be detected by underwater sensors.

Nearshore land seismometers can detect whale calls 

Two years ago, researchers discovered that even land-based seismometers along the Lower St. Lawrence Seaway (LSLS) can detect the low-frequency songs of blue and fin whales. This finding highlights a significant advantage of using land seismometers: they can record data continuously up to several years. In contrast, ocean-based instruments like hydrophones and ocean-bottom seismometers must endure high-pressure environments and are limited by battery life, typically lasting up to a year. Meanwhile, traditional whale monitoring methods, such as visual surveys conducted by boat, are often restricted to the summer months and can be inefficient. Land seismometers near the coast offer a promising alternative for tracking whale activity several kilometers from shore year-round.

To identify a certain type of whale vocalization in seismic or acoustic data, we generally use algorithms to detect and filter out whale songs from the surrounding noise. We display the sound as an image based on the frequency (or pitch) over time. When a whale vocalizes, there’s a noticeable increase in energy, and we search for these repeated energy peaks—the whale song pattern—throughout the dataset. Since datasets can be very large – sometimes up to timescales of years – often researchers will use automated algorithms to find these patterns, for efficiency.  

Spatial and temporal patterns of whale calls in the St. Lawrence Seaway

Whale calls start being detected around August. As ice begins forming in the Estuary during early winter (December/January), the whales are pushed out towards the Gulf and eventually into the North Atlantic. The wider, saltier waters of the Gulf delay sea ice formation, allowing whales to remain longer or exit to the open ocean. As a result, stations in the Northwest Gulf recorded a high number of fin whale calls (82%) and blue whale calls (95%). Blue whale detections were more concentrated in the Gulf, with some calls recorded as late as April. On the other hand, fin whale detections were more evenly distributed and ended about two months earlier.  

If you are familiar with the St. Lawrence region, or the Saguenay Marine Park, these whale call seasonal observations may seem surprising. During the summer, the area—especially around Tadoussac—is buzzing with whale-watching tours. So why don’t we hear these whales on land-based seismometers? The calls we monitor with these sensors are very low frequency (~20 Hz) and are only produced by males. Researchers believe these low-frequency sounds could serve a reproductive purpose. However, both fin and blue whales also make higher-frequency vocalizations, which are thought to be linked to feeding or prey availability. Other studies have detected these higher-frequency feeding-related calls during the summer. This suggests that both species might be using the Gulf of St. Lawrence nearly year-round when taking these different monitoring methods into account.

Changing ocean-ice dynamics and human activities

By combining the findings from current and earlier studies of fin and blue whale call detections using land seismometers in the Lower St. Lawrence Seaway (LSLS), we observed consistent spatial and temporal patterns over nearly six years (2015-2021). However, from 2019 to 2021, the duration of whale songs during the winter appears to have extended. In recent years, warmer waters have been recorded in parts of the LSLS, preventing sea ice from forming and accumulating as it usually would. The study suggests ocean-ice dynamics at play may be opening corridors for whales to stay longer in the Northwest Gulf and around Anticosti Island. Understanding where fin and blue whales tend to gather throughout the year is crucial for making informed decisions on shipping routes, reducing collisions, and mitigating noise pollution.

Sources and further reading

• Goblot, E., Liu, Y., Plourde, A., Cauchy, P., Mérindol, J., Bernier, C., Li, G., & Roth, B. (2024).  Spatiotemporal Variability of Fin Whale and Blue Whale Calls Detected by Land Seismometers  Along the Lower St. Lawrence Seaway. Seismica, 3(2).  
• Plourde, A. P. and Nedimović, M. R. (2022). Monitoring fin and blue whales in the lower St.  Lawrence Seaway with onshore seismometers. Remote Sensing in Ecology and Conservation, 8(4). 
• Ramp, C., Delarue, J., Palsbøll, P. J., Sears, R., & Hammond, P. S. (2015). Adapting to a Warmer  Ocean–Seasonal Shift of Baleen Whale Movements over Three Decades. PLOS ONE, 10(3). 
• Simard, Y., N., R., Aulanier, F., and Giard, S. Blue whale continuous frequentations of St.  Lawrence habitats from multi-year PAM series. (2016). DFO Can. Sci. Advis. Sec. Res. Doc,  (2016/091): v–14.

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