Seismic activity temporarily reshapes fin whale foraging radii

The ocean is a world of sound. For many marine animals, especially the great whales, hearing is not just a sense; it is their primary way of navigating, communicating, and finding food. In the vast, dark depths where light fails, these creatures rely on acoustic cues to locate dense patches of prey and to move safely through their environment. This reliance makes them particularly vulnerable to changes in the underwater soundscape. While human-made noise from ships and drilling is a well-known threat, the ocean is also subject to natural, powerful disturbances. Submarine earthquakes, for instance, generate intense low-frequency vibrations that travel efficiently through water. The question of how these natural geophysical events affect the daily lives of marine giants has remained largely unexplored, leaving a gap in our understanding of how the Earth's movements interact with the biology of the deep.

A team of researchers has now shed light on this connection, focusing on the fin whale in the southwestern Indian Ocean. By combining advanced computer modeling with years of acoustic recordings, they discovered that submarine seismic events cause these whales to temporarily shrink the area in which they search for food. The study reveals that when an earthquake occurs, the intense underwater noise disrupts the whales' ability to detect their prey, forcing them to confine their hunting to a much smaller, safer zone. This behavioral shift is not permanent; once the acoustic disturbance fades, the whales return to their normal, wider-ranging foraging patterns. However, the research suggests that these temporary contractions can have real consequences, potentially leading to the overconsumption of local prey and altering the balance of the marine food web.

To uncover these hidden behaviors, the scientists turned to a remote and seismically active region of the Indian Ocean, near the Southwest Indian Ridge. This area is a hotspot for both marine life and tectonic activity, making it an ideal natural laboratory. The researchers utilized a network of underwater microphones, known as hydrophones, that had been recording the ocean's soundscape continuously for months. These devices captured the low-frequency calls of fin whales, which are distinct, rhythmic pulses often described as "backbeats." The challenge was to pinpoint exactly where these whales were located at any given moment. Traditional methods of tracking whales in such a vast, open ocean are difficult and often imprecise. To overcome this, the team developed a new artificial intelligence tool called CTFusion-Net. This deep learning model was trained on simulated acoustic data to translate the raw sound waves picked up by the hydrophones into precise three-dimensional locations, effectively creating a real-time map of the whales' movements without ever needing to see them.

Using this high-precision mapping system, the researchers reconstructed the daily foraging trajectories of the fin whales over a period spanning from late 2012 to mid-2013. They calculated the "foraging radius" for each day, which represents the size of the area the whales covered while searching for food. The analysis revealed a striking pattern: on days following a submarine earthquake, the whales' foraging radius contracted significantly. In one specific instance, the day after a seismic event, the area the whales covered shrank by more than 120 meters compared to the day before. When the team looked at all five seismic events recorded during their monitoring period, a consistent trend emerged. Whether the earthquake was close to the whales or far away, the animals tended to reduce their search area shortly after the tremor. The effect was temporary; as the intense acoustic noise from the earthquake dissipated, the whales gradually expanded their range back to normal levels.

The study went further to understand why this happened and what it meant for the ecosystem. The researchers analyzed the specific characteristics of the earthquakes, such as their location, depth, and magnitude. They found that the most significant factor was not how strong the earthquake was, but where it occurred relative to the whales. The combination of the earthquake's longitude and latitude determined the intensity of the disturbance the whales experienced. The intense low-frequency sound generated by the quake likely masked the subtle acoustic cues the whales use to find their prey, effectively blinding their hearing. In response, the whales adopted a conservative strategy, staying within a smaller, more familiar area where they could still hunt, rather than venturing out into a noisy, uncertain environment.

To see if this behavioral change had a tangible impact on the ocean's food web, the team cross-referenced their findings with historical data on fish and squid populations. They discovered a compelling link: the year with the most frequent and concentrated seismic activity, 2013, was also the year when the total biomass of small fish, squid, and shrimp in the region hit its lowest point. The researchers suggest that when the whales were forced to stay in a smaller area, they concentrated their feeding pressure on the local prey, potentially depleting those resources more quickly than usual. In years with less seismic activity, the whales ranged more widely, spreading their feeding impact and allowing prey populations to remain more stable. This finding provides a rare glimpse into how natural geophysical events can ripple through an ecosystem, altering the behavior of top predators and subsequently affecting the abundance of the species they eat.

The research highlights that the ocean's health is influenced not just by biological factors or human activity, but also by the planet's own geological processes. The fin whales in the southwestern Indian Ocean are not just passive victims of these events; they are active responders, adjusting their behavior to survive in a changing acoustic environment. While the study was limited by the short duration of the monitoring period and the reliance on simulated data to train the AI model, the results offer a new perspective on ocean resilience. It suggests that natural disturbances, much like human noise pollution, can disrupt the delicate sensory world of marine mammals. By understanding these connections, scientists can better appreciate the complex web of interactions that sustain marine ecosystems and the ways in which the Earth's physical movements shape the lives of its most magnificent inhabitants.