Sunday, August 4, 2013

How do you tag a whale?

So, how do you tag a whale?Our research depends on simultaneously deploying suction-cup acoustic and movement-sensing DTAGs on the whales, but how do we actually do this?

Suction-cup mounted non-invasive DTAG3
The first thing to understand is that the pilot whales all look extremely similar.  In many cases they can only be discriminated by tiny notches or scratches on the dorsal fin, so one of the hardest things to do is make sure you tag the right whale. You often have to decide which whale to tag when it's still underwater, because you don't have time once it's at the surface.   Luckily CIRCE know the whales well, and are extremely good at identifying them.

Nicholas Macfarlane places a tag on a long-finned pilot whale
The tagger balances on the bow of Elsa, holding the tag on the end of a 5m (15') carbon-fiber pole.  While the whale is still underwater, the captain gently maneuvers the boat in such a way that when the whale surfaces it is parallel to the Elsa and within range of the tagging pole.  Then, in the instant when the water has run off the whale's body but before it submerges again, the tagger must place the tag.  Not only is the location on the whales body important, but the orientation of the tag is critical because the radio antennae must clear the water every time the whale surfaces, so that we can track the animal throughout the day.  We also have to tag the whales as gently as possible, so that they don't just breach the tags off.

Because the Strait of Gibraltar is so windy, we're often tagging in 2m swell, so the tagger has to do all of this while crashing up and down trying to keep his balance.

Oh, and our captain, Philippe Verborgh, can't see the whales or hear anyone on deck, so the tagger is wearing a headset and helping direct him.

As if tagging a single whale wasn't complicated enough, we really need to deploy tags on several group members.  This gets much harder as you tag more whales because we tend to tag the easier ones first, it's more difficult to tell which ones aren't tagged, and the whales become more evasive.

Not an easy task, and we have to do it all in a limited time window before the whales change behavior and start foraging, surfing the swell or traveling too fast for us to keep up.

Nicholas Macfarlane

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