Tuesday, 3 January 2017

Eavesdropping reveals hidden marine mammal populations in the ocean

January 3, 2017 by Joy Tripovich And Tracey Rogers, The Conversation

Acoustic monitoring of the calls of marine animals, such as whales and seals, could be the key to identifying new species, finding new population groups and mapping migration routes.

We recently used custom-designed detection algorithms to run through 57,000 hours of underwater ocean noise to find the songs of endangered blue whales, rather than listening for each whale call. This detection program saved us an enormous amount of processing time and will be critical in future acoustic monitoring research.

Some endangered marine animals, including several whale and seal species, are "cryptic species": they're genetically different but look alike. This means that they are often mistaken for one another when identified visually, making conservation plans difficult to implement.

However, most animals produce species-specific calls. Eavesdropping on their calls therefore provides a unique way to monitor them. This is completely rewriting our understanding of their population recovery.

Recovery of the blue whale
We recently discovered two new blue whale populations migrating off the east coast of Australia using this technology. This is important news as the blue whale has been slow to recover after being hunted to the brink of extinction. How can the largest animal that has ever lived, the Antarctic blue whale, swim undetected just off the coast of Sydney?

It is remarkable that we have only now discovered them there. It is possible that they only started using this route recently, or perhaps they have been there all along and we have missed them.

Fortunately for us, blue whales sing, allowing us to detect them using arrays of listening devices spanning sites across the Indian and Pacific oceans. However, the frequency of their song is so low that humans can't hear it.

Blue whales produce different calls and these calls possibly reflect different subspecies. Their different songs help the International Whaling Commission manage the recovery of these subspecies.

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