Monday, 8 September 2014

Tag count 1!

Huge progress over the past few days! The team's hard work has really paid off with four more tags successfully deployed over the past 48 hours. That brings our total to 9 tags deployed - with 8 of them having transmitted humpback whale locations to us via the Argos satellite system. Great work TEAM!

Our track data are already revealing several interesting results. One of the whales (tag 87777.14) has already started migrating away from Rarotonga...to the NORTH! This is a brand new insight into Rarotonga humpback movement behavior given that all seven of the 2007 whales headed away from Raro in a west to northwest direction (see map below). In fact, 87777.14 is charting an entirely new course - and a bewildering one at that - as we'd expect these whales to start moving SOUTH in Spring, not north.

Preliminary map of 2014 and 2007 humpback whale satellite track data. One of the 2014 tagged whales has already left Rarotonga, heading north! (yellow circles, 87777.14)

Another interesting early result is the movement velocity of these whales. My preliminary analysis suggests these whales migrate at speeds around 5 km/hr, based on both the 2007 and 2014 migratory movement velocities (see below graphic). However, when they are hanging around Rarotonga, the data indicate that the whales swim at slower speeds, closer to 2 km/hr. This is an interesting result as it can help us follow whales around the island and anticipate where they will next come to the surface for a breath. These results also provide a possible means of differentiating migratory behaviors from non-migratory behaviors. Cool!

Preliminary distance versus time plot for the class of '14. Constant slopes on this plot represent constant swimming speeds (i.e. movement velocities). All of the migrating 2007 whales maintained swimming speeds of ~5 km/hr, just like 87777.14 has done over the past few days (non-stop mind you!).

But that's not all we've been discovering! Our longest track so far is for a whale that hasn't even left Raro yet (and who can blame it?). What's neat about this one's track is that we can study it to better understand the movement behaviors in the waters around the island. It seems this whale (81126.14) might be a reincarnated albatross - it seems perfectly content circumnavigating the island every few days! By studying this whale's movements in unprecedented detail we can start exploring patterns in its behavior: go clockwise if...; turn around when...; stay put in response to...etc. We've never had data of this spatial and temporal quality before so even these 'local' movements are tremendously exciting!

81126.14 circumnavigates Rarotonga! This loop took 2.5 days at a relatively constant swimming speed of 2 km/hr. It did play pinball off Fruits of Rarotonga on the 248th day of the yea - so it could make a full circuit in about 1 day of non-stop swimming at this cruising speed.

And for those of you thinking about taking a trip to Rarotonga some day, be sure to stock up on your Hawaiian shirts and dresses while on the island! It's become a tradition in our family!

Zach, Katie, and Maddy model this year's line.
More to come in the week's ahead folks!  Stay tuned....