Each year, during summer and fall, large groups of baleen whales gather off the coast of California, U.S., to feast on krill and fish before heading south to breeding areas in the tropics. It’s a crucial time for whales to fatten up, and a new study suggests some whale species announce an abundance of food with songs — but when food supply drops, so do the songs.
Researchers focused on humpback whales (Megaptera novaeangliae), blue whales (Balaenoptera musculus) and fin whales (Balaenoptera physalus) to determine which environmental conditions most influence how frequently whales sing.
They used recordings from underwater microphones called hydrophones that can detect any whale song for thousands of square kilometers (square miles).
They also used photos of whales collected by researchers and citizen scientists, and NOAA Fisheries data on prey availability. They wanted to understand how whale songs may be influenced by factors like changes in the number of whales present, the duration of their stay between migrations and food availability.
Analyzing six years of data, the study identified a clear pattern.
For the first three years of the study, “times were tough” for whales, John Ryan, the study’s lead author and a biological oceanographer with the Monterey Bay Aquarium Research Institute, told Mongabay by phone. A marine heat wave and a toxic algal bloom led to a decline in both fish and krill populations and whales sang less.
Over the next three years, the second half of the study, the krill population rebounded, leading to more singing across all three whale species. However, when krill numbers declined again, blue whales, which feed exclusively on krill, sang less. At the same time, fish population surged and humpbacks, which consume both small fish and krill, continued singing.
Ryan said it’s hard to know why whales sing more with more food. Possibly, when food is limited, whales need to dedicate more time to foraging and don’t have as much time to sing.
In a related study, scientists have found that whales call to other whales to let them know where the food is good, which “allows the local population to collectively search a vast foraging habitat.”
When blue whales encounter a huge krill swarm, they make a specific call, which Ryan said essentially says, “Hey, my fellow blue whales, I am yumming it up here. Krill’s up.” Using drones, scientists have observed blue whales responding to the call “streaming towards this foraging opportunity,” from miles away, he added.
Andy Rogan, a marine mammal biologist with Ocean Alliance who was not involved with the study, said this research provides a valuable tool for whale conservation.
“Being able to draw relationships between increases in whale song – and shifting prey abundance/distribution is very valuable: just from picking up whale song you can start to make more inferences about the broader ecosystem,” Rogan told Mongabay by email.
Banner image of a humpback whale by Whit Welles via Wikimedia Commons (CC BY 3.0).
Credits
