Monday, September 30, 2013

Basking shark tag recovery

Andrew Westgate, wandering tag in hand.

Last week, an old friend emailed an offer I couldn't refuse.  A basking shark (Cetorhinus maximus) tagged off Grand Manan in the Bay of Fundy, had gone on walkabout.  The pop up tag, designed to float free after a few days recording the shark's behavior, was phoning home.  Andrew Westgate, from UNCW and the Grand Manan Whale and Seabird Research Station, was on a quest to get it back.  And I got to ride along.  (Dory stayed at the doggy hotel, having her spots polished, as Damon likes to say.  He was at Kent Island.)

Basking sharks, bizarre and extraordinary, are the second largest fish on the planet.  And they grow to such great lengths -- 40 feet -- not through spectacular and gruesome acts of predation, but through filter feeding.  The "basking" in basking shark comes from their habit of spending so much time on the surface (Andrew's tags indicate they can spend as much as 40% of their time there) and the leisurely pace of their swimming.  In the Gulf of Maine, basking sharks concentrate there foraging on Copepoda, using modifications to their gills called rakers.  (Want to see more?  Check out this nice documentary.)

In an apparent case of convergent evolution, basking sharks are remarkably similar to right whales.  (Which gets me wondering what mechanism prevents them from competing for the same niche while they are in the Gulf of Maine.)  Both are ponderously large, slow-moving, surface dwelling plankton eaters.  It's no surprise, then, that basking sharks face many of the same threats as right whales:  over exploitation, entanglement in surface fishing gear, and ship strikes.  So learning more about their behavior is an important step towards conservation of the species.  

Andrew's group started researching basking sharks in the Bay of Fundy in 2008; deploying tags that record behavior on a short time scale; other tags that record location over several months; and conducting aerial surveys in the Gulf of Maine.  They also are assembling a photo-id catalog of dorsal fins, because it turns out you can track an individual over time through the unique fins (as you can bottlenose dolphins by they fins, or humpback whales by their flukes).

The tag we were hunting for was floating some 40+ miles southeast of Mount Desert Island, sending its location up to satellites.  Andrew chartered Osprey, the College of the Atlantic's outstanding new research and teaching vessel, to go after it.  We lucked out with the weather -- a late September's day was never so fair as last Saturday:  70 degrees and northwest winds 0 - 5 knots.  It wasn't quite a Beaufort 0, but it was close -- nearly flat calm.  We left Bar Harbor under the shadow of two enormous cruise ships and headed out past the cliffs of Acadia.  Lobster bouys peppered the water until we reached Mt Desert Rock, where they slowly petered out.  Cadillac Mountain, a looming monster on land, grew smaller and smaller, then was no more.  Herring gulls grew less common and pelagic birds flew by to check us out.

College of the Atlantic's amazing research and education vessel.

Osprey's crew.

Andrew and Captain Toby Stephenson discuss the plan of action.
It might seem like finding a tag the size of a cucumber would be the proverbial needle in the haystack, but we found the tag with no problem.  A couple of miles from where we expected to find the tag, Andrew donned his headphones and tracking gear to pick up the radio signals the tag was emitting.  He was able to pick up a good signal and point the boat towards the tag, which we simply scooped up with a net.  (The tag was entrained in a raft of seaweed, just as Andrew said it would be.)  I'm sure it was a moment of relief for Andrew when we brought it aboard.  He never expected a shark would carry it so far offshore or so far from home.

Andrew listening for radio signals with a "yagi" antenna.

Quarry captured.  Phew.

Explaining how the tag works.

I'd call, wouldn't you?
 Beyond the tag, it was a spectacular day for wildlife.  Humpback whales, white-sided dolphins, pilot whales, two -- yes two -- encounters with Mola molas, and a blue shark.  I rarely get to head so far offshore, and never on such a nice day.  With the seas so calm, we could see disturbance on the water far in the distance -- a hint that wildlife was probably there.  One of the pleasures of the day was spending time with a crew who was as fascinated by the animals we encountered as we were.  Any little hint of a whale sent us off to investigate.  Osprey was a sweet ride with a terrific crew.

Taking photos of humpback flukes for photo id.

Looking the fluke catalog to determine who it was.

Pilot whales.

Atlantic white-sided dolphins.

Mola mola!  MOLA MOLA!

One of our humpbacks.
 Alas, it had to end.  We steamed into Bar Harbor (past an enormous cruise ship on its way out) just as the sun was falling behind Cadillac Mountain.  It was a satisfying day all around -- tag recovery, amazing wildlife, and a visit with an old friend.  Any other old friends want to let me "tag along" -- just call me.  I'll drop my grading and be right there.

Tourists on a sunset cruise.

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