Whales of the deep: analyzing movement and diving of humpback whales to understand oceanic breeding congregations in New Caledonia

Humpback whales’ (Megaptera novaeangliae) habitat use in low-latitude breeding grounds is well documented from decades of coastal research. Yet, the use of pelagic habitats during the breeding season and migration has only recently been given attention.

In New Caledonia, an archipelago located in the Pacific South West, several seamounts and banks play an important role for the local humpback whale population. Yet, the reason why whales would aggregate and move between these offshore waters remains unknown. The relative abundance of maternal females in these unsheltered waters is also puzzling, in comparison to the shallow coastal waters usually occupied by these groups.

Using the newest satellite tracking technology, this project aims at understanding the environmental and social drivers of humpback whale oceanic habitat use during the breeding season. Dive depth will be related to environmental context in order to shed light on the role played by offshore seamounts for humpback whales of the Pacific South West.

This study case will provide a unique opportunity to understand the spatio-temporal scale of the humpback whale floating lek systems and explore the drivers of habitat selection during the breeding season.

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This work is part of the WHERE project supported by the New Caledonian Government, the French Ministère de la transition écologique et solidaire, the World Wildlife Fund.

The « Whales of the deep » project is specifically supported by the Society of Marine Mammalogy (Louis M. Herman research scolarship).

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August 2018 update

[by Solène Derville]

It is now been more than two months since the first humpback whales showed up in New Caledonia for their annual breeding season. In July, our team composed of members of the French Institute of Research for Development, the Opération Cétacés NGO and the World Wildlife Fund, left the Nouméa harbour aboard the Amborella. This year again, the New Caledonian government supported our project by providing this large vessel, which allows us to survey in the open ocean.

The goal for this cruise was clear: deploy 6 satellite tags on adult humpback whales at the Antigonia seamount (see previous blogpost). Tags are deployed on adult whales only, at the front of the dorsal fin, using a modified pneumatic line-thrower (called “ARTS”, see video below). While being tagged, whales are also photographed and biopsied in order to obtain the sex (through molecular sexing from the skin sample) and the identity (through genotyping and photo-identification) of the animal. These informations are essential to reconstruct the “capture history” of the tagged whales, that is where and when it has been observed in the past.

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Claire, Rémi and I are preparing the tags for the next day. We are not letting ourselves get distracted by the beatiful scenery of the Isle of Pines in the background!

Despite rough weather on thThis short video presents the method for tag deployment from a small semi-inflatable boat using a modified pneumatic line-thrower. The crossbow is used simultaneously to collect a biopsy sample (a small piece of skin and blubber).e first day (20 knot wind and big swell!) we managed to deploy two tags. The others followed on the next day at sea. Tagging 12 m long whales is one of the toughest job I have ever witnessed in the field. A great level of precision and communication among crew members is essential for this task to succeed. So you can imagine our joy when we managed to deploy 4 tags in a single day!

This short video presents the method for tag deployment from a small semi-inflatable boat using a modified pneumatic line-thrower (in 2017 for whale « Sial » and 2018 for whale « Gondwana »). The crossbow is used simultaneously to collect a biopsy sample (a small piece of skin and blubber).

One unexpected challenge that follows tagging is… finding names! For this year’s batch we went for the “geology theme”, with a special South Pacific touch… Whales were nicknamed: Pangea, Gondwana, Zealandia, Oceania, Nazca, and Tethys. Hopefully lucky names that will make these tags last for long!

Once the tags deployed we were free to use our remaining time at sea to visit other areas. We therefore decided to visit the Ellet seamount near Walpole Island (see previous blogpost), a previously unsurveyed seamount that had been used by a whale tagged in 2016. Surely enough, whales were found there! Photographies and skin samples collected there will help us understand the connexion between this new seamount and neighboring pelagic breeding grounds.

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Photo of a tagged humpback whale. The top of the tag is visible, as well as the rocket that detached on impact and the arrow that contains a tiny skin sample!
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