The hungry whale is the silent whale, according to the study. The study reveals that whales vocalise less amid the strong ocean heatwave to kill their prey which creates a barometer of the effects of climate change on the ecosystems. Scientists at the Monterey Bay National Marine Sanctuary along California’s central coast are rich feeding grounds for fin, blue, and humpback whales. They migrate along the shore each year. Because sound is whales’ principal way of communicating and navigating, they create complex sounds or songs when they find food and a mate.
Besides their physical attractiveness and ethereal melody, they create, whale songs are also a glimpse into their lives, giving the information about their adaptability in the face of a marine heatwave and susceptibility to shifting environmental demands. Whale songs are valuable information to know how climate change is affecting the seas and their ecosystems.

Role of whale songs in monitoring ecosystem changes

Researchers at the Monterey Bay Aquarium Research Institute (MBARI) and others compared recordings of whale song within the ocean sanctuary from 2015 to 2021. This was during a marine heatwave, a phenomenon brought about by climate change, that wiped out the major prey species populations such as krill, anchovies, and sardines, all of which belong to the whales’ diet.
Whales are at the center of the carbon cycle process in oceans. The ocean absorbs almost one-third of Earth’s carbon dioxide emission and 90% of ensuing pollution-causing generated heat. The growth of organisms chewed by the carbon is maintained by whales and supplemented by nutrient-rich waste.

Whale songs act as indicators of ecosystem health and climate change

The marine heatwave resulted in a major interruption in the whales’ food availability. With prey populations dropping dramatically, whale vocalisations reduced. John Ryan, an MBARI biological oceanographer and author of last month’s peer-reviewed paper on PLOS One, elaborated, “The whales all had the lowest levels of song when things were worst.” But as the intensity of the heatwave decreased, whale song increased. This has a very direct correlation underlining the value of whale songs as an indicator of ecosystem health and of climate-driven change.
Ryan observed that whales, which undergo extreme changes in their environment, serve as “ecosystem sentinels,” giving an early signal regarding marine ecosystems’ health. Such information would be useful to scientists in tracking variations in whales’ migratory patterns and if whales are leaving feeding grounds for areas where prey is more concentrated. If they’re fleeing to a new location where there’s more prey, then we need to determine that so we can defend those refuges,” said Vanessa ZoBell, a postdoctoral scholar at the Scripps Institution of Oceanography’s Whale Acoustics Lab at the University of California at San Diego, who was not involved in the research.

How whale songs reflect shifts in diet and ocean health

The most significant challenge of this study was isolating whale songs within the harsh environment of the sea. Scientists used machine learning tools created by the National Oceanic and Atmospheric Administration (NOAA) and Google’s artificial intelligence groups to sift humpback whale songs from other ocean noises. They further compared data collected by NOAA in its long-standing survey of whales’ prey including krill and anchovies in order to see how the rate of whale song is related to their prey numbers.
Aside from underwater microphones, scientists employed crossbows with darts mounted on them to obtain skin samples from whales, and these served to confirm shifts in their diets during years of food abundance or deficiency. Analysing the samples as well as patterns in the songs, the scientists were able to discern evident correlations between the presence of food and whale song frequencies.
ZoBell explained that the whale songs would be useful indicators of biodiversity and ocean health if the whales stop producing them. It would indicate major ecological shifts in the region if the whales stop singing. “If all those sounds disappear, it kind of alerts us that a change may be occurring in an area,” ZoBell said.

Whale songs and the importance of food sources

Blue whales, the largest creatures on Earth, rely on krill, small crustaceans. When the krill populations bounced back following the heatwave, scientists recorded the return of blue whale songs. Once the krill populations waned again, the occurrence of their songs reduced. In contrast, humpback whales, who also feed on anchovies and sardines, had a comeback in their vocalisations when their populations boomed.
Ryan underscored how whale song was important for reproduction, sociality, and food gathering in whales. Failing to produce the song indicates difficulty, since the whales must consume plenty of food energy in order to sing the complicated vocalisations. “A whale cannot expend energy on song if it is more effort to find the food it takes to fuel a body that weighs in excess of 300,000 pounds,” Ryan said.
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