MEDITERRANEAN — Sperm whales in the Mediterranean Sea exhibit two distinct coda dialects, according to an analysis of hydrophone recordings from 2003 to 2021. Researchers analyzed recordings made over 112 days from both the Hellenic Trench near Greece in the eastern Mediterranean and around the Balearic Islands off the coast of Spain in the western Mediterranean basin. The study was published in the journal Proceedings of the Royal Society B.

Most sperm whale codas in both regions utilized four clicks. Whales in the western Mediterranean basin used a 3+1 coda, characterized by three regularly spaced clicks followed by a longer pause and then another click. In contrast, whales in the eastern Mediterranean basin generally employed a faster version of this coda. Some codas were primarily restricted to either the eastern or western groups, though eastern basin whales occasionally produced the western dialect.

Genetic studies previously indicated that Mediterranean sperm whales, an endangered population numbering a few thousand individuals, have become isolated from other sperm whale populations. There are signs that mating between sperm whales in the western and eastern Mediterranean basins is restricted. Individual sperm whales have been spotted moving between the two regions. Sperm whales are believed to have entered Mediterranean waters approximately 20,000 years ago.

"The dialect is used to form social structures, within which these animals will cooperate," said Dr. Luke Rendell, of the University of St Andrews and a co-author of the new study. "This is the first example we've got where we can look at a snapshot and think: 'Oh, this seems to be telling us about how new dialects come about'."

Rendell noted that while the eastern whales retain elements of older patterns, they have also evolved a slightly different version of the coda. "The whales in the east remember the old ways, but they're moving on and they've got a slightly different version of what is clearly the same [general type of coda], but they've evolved it a little bit; they've changed it," Rendell said.