Life history and decline of killer whales in Crozet Archipelago, southern Indian Ocean

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We have done demographic analysis to try and determine more precisely the tendencies followed by the killer whale population of the Crozet Archipelago. In order to do this we have used a photo-identification program that started in 1964, which consists in identifying all individuals regarding the marks and scars beared on their dorsal fin and their dorsal patch.

© photo Christophe Guinet

The analysis made indicate that in ten years, the population has droped from 93 individuals in 1988-1989 to 43 in 1998-2000. A killer whale was living on average 60 years ten years ago, today its lifespan is less than 20 years.

This decrease in survival may be partly apparent if the missing individuals from different pods have left coastal waters of Possession Island. However, this hypothesis is not likely as killer whale pods have the characteristic of being socialy very stable and only a few individuals are missing in several pods, which emphasise the hypothesis of an increase in death rate.

The combination of several factors could be responsible for the decline of this killer whale population around Possession Island:

1) The decline of their main preys: large baleen whales due to past whaling, and southern elephant seals (Mirounga leonina) from the 60’s to the 80’s;

2) Mortality induced by recent interactions with the Antarctic cod (Dissostichus eleginoides) longline fishery. Killer whales (but also sperm whales) understood that they could feed at lower cost by picking up the cods off the line while they are winded up.

Our analysis indicate that the situation of the killer whales is critical and has gotten worth since the development of illegal fishing - fisheries inspectors are present on boats allowed to fish in the Exculsive Economic Zone. This population is demographically unstable with a lack of recruitment (no juvenile) and a progressive loss of all the females likely to reproduce, which makes us worry about the loss of these killer whales.

© photo Christophe Guinet

A recent event strengthens our worries with the inspection of the Praslin, a fishing boat known for fishing illegally in the TAAF and temporarily placed under arrest in Mauritius for illegal posession of explosives. These explosives are used to "frightened" and most likely to eliminate the killer whale problem. The Crozet killer whale population has been followed for more than 30 years now.

We wish to inform you about this situation, of wich Mr François Gardeso is concerned about, superior administrator of the TAAF, so that fast and clear measures can be taken in order to insure the conservation of this killer whale population, and in extense, of these polar marine ecosystems that has been under systematic pillage in the more recent years.

Christophe Guinet
In charge of research at the CEBC-CNRS