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Days 15 and 16: 09-10 Sept 2013 Jour 15 et 16: 09-10 Sept 2013

Posted by: | September 11, 2013 | 2 Comments |
humpback underwater

humpback underwater

 

Yesterday was our first day working at Rurutu. We were pleasantly surprised to see a familiar face (or fluke, as the case may be) from Tubuai.  One of the whales we had encountered four different times at Tubuai was here at Rurutu yesterday.  The last time we saw this whale was five days ago on the 4th. We don’t know when, but sometime during that five-day period the whale traveled 200 km to Rurutu. We also encountered separately, two yearlings, and were able to biopsy one of them. In total we collected three skin samples and two fluke identification photos.

 

This morning off the south side of the island we had an encounter of an adult with a young whale (not the same two we saw yesterday). We were able to collect biopsies from both individuals and fluke photographs of the adult. We then headed north and found a singer. We recorded 50 minutes of song (parts of which we hadn’t heard before, and other parts that sounded similar to Moorea’s song in 2011!) before collecting a fluke identification photo of this individual. We decided to circumnavigate the island, and on the southeast side of the island we encountered a mother calf pair accompanied by two escorts. It was clear that one escort was the “odd man out”, remaining at some distance from the other three whales, and once during the encounter he breached very close to our boat (out of frustration?). The primary escort was the closest to the mother and was extremely aggressive, using its large body size to come between the mother and calf several times. A few times the primary escort raised its head out of the water, bringing it back down on the calf, submerging the calf below the surface. Another time the primary escort lifted the calf completely out of the water (see photo).   The calf attempted several tail slaps towards the escort, and the mother tried to force the escort away from the calf, but none of these efforts were successful. We had to leave the group in order to go back to the marina, so we do not know how the incident ended.

 

The humpback calf lifted out of the water by the escort

The humpback calf lifted out of the water by the escort

Ce matin nous sommes tombés sur 2 baleines à la pointe sud de l’île, dont une était un des jeunes vu hier.  On a pu obtenir une biopsie des 2 individus ainsi qu’une caudale de l’adulte. Plus au nord, nous avons trouvé un chanteur et avons pu enregistrer environ 50 min de son chant (dont certaines parties n’étaient pas sans rappeler le chant entendu à Moorea en 2011). Après avoir travaillé sur cet individu nous avons décidé de continuer pour un tour de l’île. Grand bien nous en a pris car nous avons rencontré une mère et son petit accompagnés de deux escortes. L’un des mâles adultes ne semblait pas faire le poids à côté de son congénère, et ses sauts en marge du groupe n’y on rien changé. Le deuxième mâle c’est quant à lui montré très agressif vis-à-vis du petit, tentant notamment de le séparer de sa mère. On l’a aussi clairement vu essayer de submerger le petit de force. A un moment, il l’a même sortie complètement de l’eau en le soulevant avec ça tête (voir photo). Les battements de queue du petit paraissaient bien dérisoires par rapport à la puissance dégagée par l’escorte. Devant rentrer à la marina, nous ne savons pas ce qu’il est advenue du petit.

A humpback whale showing the proximity of whales to shore. The cliffs typical of Rurutu in the background.

A humpback whale showing the proximity to shore. The cliffs typical of Rurutu in the background.

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2 Comments

  1. By: Scott on September 11, 2013 at 2:43 pm      Reply

    Aggression towards a calf by an escort is rare in my experience but I have often wondered why. How did the mother react?

    • By: Renee Albertson on September 15, 2013 at 10:04 am      Reply

      During the encounter that we observed, the calf’s mother repeatedly attempted to place herself between the escort and calf, but was not very successful.

      Physical aggression by an adult male directed towards young has been observed in a variety of mammalian species, including lions, langurs, baboons, chimpanzees, leopards, and squirrels. In cetaceans (whales, dolphins, and porpoises) this type of behavior has been observed in bottlenose dolphins, tucuxi dolphins, Guyana (“Costero”) dolphins, and humpback whales.

      In some cases the aggression can result in the death of the young – this is referred to as ‘infanticide’. Although this aggression seems brutal, it has an evolutionary logic. In general, lactating females do not ovulate and therefore cannot become pregnant. However, if a lactating female loses her calf, ovulation can be induced outside of her normal cycle, and if a male mates with her, she can become pregnant by him. In this scenario there may be two benefits to the aggressive male—he eliminates the offspring of some other male in the present season, and he himself will be the father of the new calf that will be born in the next season.

      Humpback whale male aggression towards calves has been observed on breeding grounds near Hawaii and Costa Rica in the North Pacific, and at Moorea and Rurutu in French Polynesia, South Pacific. To our knowledge, the only suspected (but unproven) death of a humpback calf that may have resulted from an aggressive encounter with a male escort was at Costa Rica.

      —The Research Team: Michael, Marc and Renee

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