Tuesday, 7 October 2014

Migration Update #4

Has the migration finally begun?

It seems most of our tagged whales are perfectly happy continuing to bounce between the islands of Oceania. 112716.14 continues to hang out around the small islands of northern Tonga, 112697.14 has joined the party in Samoa, and 87777.14 has shifted over to Atiu from Aitutaki in the southern Cook Islands.

121195.14 is the whale I have my eye on most at the moment. It has started swimming away from Samoa in an overall southeasterly direction. It could very well stop-over in Niue over the next few days - or it might very well keep on going all the way to the Antarctic. We'll have to wait and see if the southward migration has well and truly (finally!) begun, or if this is just another (truly remarkable!) example of island hopping...

Oct. 7, 2014 Humpback Whale Track Map 

I've updated the cumulative distance graphic as well (see below), in addition to the satellite transmission pie charts (further below). The cumulative distance plot continues to show that the open-water movements are faster than the near-shore movements - eventually I will do a piecewise linear regression breakpoint analysis on these distance versus time plots to objectively identify changes in the behavioural states of the whale movements (free from all the problems of state-space modeling and other forms of interpolation!). Meanwhile, the satellite transmission pie charts haven't changed very much (despite there being three times as many total transmissions received since my last update). This indicates to me that the current pattern of transmission quality/distribution should continue as long the whales stay in this sector of the South Pacific Ocean. As the whales start moving out of Oceania, however, the satellite transmission window gets broader and we might very well see an increase in the quality/number/distribution of the transmissions received. Maybe next week...

Cumulative Distance traveled versus time plot. Steeper slopes equate with faster open-water movements, lower slopes equate with slower near-shore movements.

An update to the Argos satellite transmission distributions and location data quality (for those techno-gearheads out there; Hi, Dad!)
And speaking of Papi (what the Grandkids call my Dad - who is also named Travis), I have changed the 'inferred' path taken by 87777.14 in the updated map at the top of this post. I agree, Papi. There's no evidence to suggest 87777.14 took such a tortuous (i.e. sinuous) course during the period that it's transmitter tag went silent. All the other data would suggest that something more like the inferred (yellow dashed) path shown in the map above is more likely (than what I had previously inferred). That said, we'll never be able to prove it one way or another...

I'm gonna getcha. Gonna getcha, getcha, getcha, getcha, next week. Or another. Gonna find ya...