Scientists find blue whales suddenly going silent. Why they think it's happening.

Indianapolis Star

10 hours ago

Changing ocean conditions making whale prey scarce are causing the mammals to stop singing, a recent study has found.
Researchers at the Monterey Bay Aquarium Research Institute, Cascadia Research Collective and other national institutions spent six years monitoring the acoustic sounds of blue, fin and humpback whales off the California coast from July 2015 to June 2021, according to a study published in February.
Researchers set out to determine whether the frequency of whale songs changed seasonally and whether that frequency was indicative of changes within marine ecosystems.
As a result, scientists found the levels of whale songs among different species correlated with their ability to locate and consume prey.
Marine biologists began the research in 2015, when a marine heatwave dubbed "The Blob" caused a large percentage of krill — teeny, shrimp-like creatures — to disappear. Humpback, blue and fin whales largely depend on krill as a primary food source.
The heatwave disrupted ocean circulation patterns, which impacted the number of cold, nutrient-rich waters that support the small crustaceans, according to the National Oceanic and Atmospheric Administration (NOAA).
This led to a scarcity of food supplies for fish, seals, penguins and whales.
Additionally, increasing temperatures contributed to the spreading of a toxic algae bloom between 2015 and 2016 in the northeastern Pacific, leading to the most widespread poisoning of marine mammals ever documented. In 2015, NOAA confirmed a then-record 53 instances involving whales getting caught in fishing gear.
The following year, the agency found 55 instances in which whales became entangled.
As humpback whales can switch between feeding on krill and fish, like sardines and anchovies, they experienced the most positive song detection trend throughout the six-year study.
However, blue and fin whales, which are larger than humpback whales, did not exhibit the same positive trend. The two species are more specialized in foraging for krill. With the declining prey population, they were forced to spend more time hunting, leaving little time for singing, researchers found.
There is concern for similar patterns to continue as ocean temperatures continue to increase over time. Marine heatwaves also occurred in 2018 and 2019 during the summer months, when whales fatten up on krill to prepare for the rest of the year, according to NOAA.
In a report issued in June, the agency revealed a steep decline in Pacific gray whales. A new count suggests there are about 13,000 gray whales, the lowest number since the 1970s. In 2019, there were about 20,500 gray whales.
From 2019 to 2023, the species suffered from an Unusual Mortality Event that scientists say stemmed from localized ecosystem changes in Subarctic and Arctic feeding grounds. Gray whales rely on prey in the area but changes in the ecosystem caused widespread malnutrition, reduced birth rates and increased mortality.
In other parts of the United States, there are signs that similar issues might be occurring.
Earlier this month, a boat in Barnegat Bay, New Jersey, struck a 26-foot-long minke whale that ventured into shallow waters. Preliminary necropsy findings indicated the mammal was thin with an empty gastro-instestinal tract and little digestive material present, the Marine Mammal Stranding Center, the organization that conducted the testing, found.