The recording was made on 18 September by Hilla Pallas, 68, whose small listening station was built to track engine noise, not whales. By Monday, a review of the sound had helped bring 39 squid-fishing boats into a voluntary 72-hour pause in a 9-kilometre (5.6-mile) corridor off Nagasaki Prefecture.
Pallas has spent 27 years on Iki, an island known for fishing and low green hills, carefully noting sounds that most harbour visitors miss. She placed the hydrophone cables herself and checks the recorder each morning, usually with a mug of tea beside its flickering display. The whale calls, she said, sounded like “a room suddenly filling with voices”.
The count no one expected
The station captured the calls between 20:00 and 07:00. Its tally of 1,306 distinct vocal events was 5.4 times the highest monthly count recorded there since 2019. The number does not represent individual whales: calls can overlap, and one animal may call repeatedly. But the recording contains at least 19 separate sequences that marine specialists judged consistent with fin whales.
Jiří Hlávková, a marine ecologist who reviewed the audio, said the cluster was unusual for the season. “We expected scattered calls, not an overnight chorus at this scale,” she said. The recording cannot prove how many animals were present or whether the same group stayed in the area. Still, its timing and strength prompted fishing representatives to ask for a short pause.
I built this to listen for engines. That night, the sea answered back.
Hilla Pallas, sound technician
The twist is that Pallas was not searching for whales. The recorder had been installed to help compare harbour engine noise with complaints about late-night boat traffic. She had nearly dismissed the first bursts as interference, then replayed them and heard a repeated low, rising call. She sent the file for review before dawn.
A pause across the strait
The fishing halt began on 22 September, after local representatives agreed to keep boats out of the marked corridor for three days. Twenty-two Japanese vessels and 17 South Korean boats took part, according to Livia M. de Vrome, a bilingual fisheries mediator who helped coordinate the talks. The pause ended on Thursday, with crews reporting no gear or boats lost.
The Tsushima Strait, between Japan and the Korean Peninsula, is a heavily used route for fishing and shipping. Competition over seasonal catches has made cooperation difficult, but this was a limited practical agreement, not a treaty or a ban on fishing. The participants will meet again in October to discuss whether a second pause is warranted.
Pallas said the recorder will keep running, though she has no plans to turn it into a permanent whale-counting project. A second listening unit is being tested on the island, and Hlávková’s team is checking whether the calls match recordings from other parts of the strait. For Pallas, the result is already personal: “I thought I was measuring what made the harbour loud. I found out what we had been failing to hear.”
