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Monday, November 27, 2006

Whale workshop at SPC Noumea today

We're hosting a workshop on whales today, at our conference centre in Noumea, New Caledonia.

More specifically, a workshop co-organised by the South Pacific Whale Research Consortium and "Opération Cétacés - Nouvelle-Calédonie", to develop a protocol for the comparative photoidentification of humpback whales and a catalogue of individuals in the South Pacific, with the hope of arriving at a census of the population of humpbacks travelling within the region.

There was a beautiful video screened during the opening ceremony, which used local footage and which I hope I can get my hands upon later.

We (SPC) don't have a lot to do with baleen whales ourselves, in fact we don't have a lot to do with marine mammals in general nowadays. When our environment programme moved to Samoa in the early 90s they took all of the work-area on threatened and endangered marine species with them.
Our fisheries programmes still have a bit of an interest though, because interactions between tuna fishing boats and some of the smaller toothed whale species seem to be more common nowadays.

I don't mean the kind of interactions that used to happen in parts of the eastern Pacific tuna fishery where purse-seiners used to target porpoise schools because of their association with tuna. Porpoises are not good indicators of tuna schools in the western Pacific, and purse-seiners target tend to target floating objects here, like drifting logs, or man-made fish-aggregation devices, when they are not targeting free-swimming schools of tuna.

No - I'm talking about the kind of interaction that seems to be entirely in the marine mammals favour, where pods of pilot whales traverse long-lines, "cherry-picking" the fish off the hooks.

I've never heard of any whales being hooked up themselves while they are doing this - they seem to know exactly how far they can go, and they usually leave the head of the tuna on the hook, neatly sheared off behind the gill-covers. Sharks will also take fish off hooks of course, but sharks don't seem to be half so clever about it. Sharks often get hooked up themselves, or they leave a ragged, sniggled carcass on the line - very different from the clean table manners of toothed whales.

The other difference is that sharks don't operate as a group. They'll take fish here are there, but if a pod of pilot whales discovers a longline they will often strip the entire line of fish, and then move onto any nearby boats. The only remedy is to head for the hills, and I've heard of boats steaming for hours trying to shake off a pod of whales.

From the figures I've seen so far, whale predation does not appear to be a huge problem for tuna boats. It still appears to be less than shark predation overall. But where shark predation is diffused across the whole area, whales predation seems to be locally intense. And many fishermen reckon that shark predation is decreasing along with shark populations, but whale predation is increasing in intensity - they reckon that the whales learn this behaviour off each other.
Of course whales have always been partial to a bit of commensalism with their human colleagues.

And "interactions" with killer whales have long been a feature of the Mediterranean bluefin tuna fishery.

I'd be very much interested to know how much whales DO learn this behaviour off each other - whether it is social learning - or individual learning based on instinctive feeding patterns.

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