It’s 12:30 a.m. My PhD advisor is at my bunk-side. “Julie,” he says, “we got one of the tags, and we can hear the other. You’re up.”
I wish I could say that I had just been woken up for what was a scheduled watch shift, which is typical of many research cruises. Unfortunately, the business of whale tagging does not fit a schedule, but instead involves, as my last three weeks of work off New Zealand’s east coast can attest, many unpredictable sleepless nights.
On the east coast of New Zealand’s South Island sits the Kaikoura peninsula, an undersea trench that juts into the continental shelf. The Kaikoura canyon’s high-nutrient, upwelling waters support a rich and diverse marine community featuring a resident population of the world’s largest predator: the sperm whale.
With support from the local whale watching community, and in collaboration with researchers from the University of Otago who have studied the Kaikoura sperm whales since 1990, it was our goal to study how these animals use their habitat. On top of that, we hoped to test some new methods to measure acute and chronic stress in a wild population. One of the tools in our arsenal, and the one that had just woken me from an hour’s nap, is the DTAG — a digital acoustic recording tag developed at Woods Hole Oceanographic Institution — which records an animal’s movement in three dimensions and the depth to which it is diving. The tag also records sound through a hydrophone, capturing both the sounds produced by the tagged animal and other sounds that it can hear.
We had tagged two large male sperm whales that day. Deployed with a hand-held pole and attached via suction cup, the tags were programmed to release from the animals around 6 hours after they hit the water. The tags can be tracked by VHF (very high frequency) beacon, emitting beeps whenever they break the water’s surface. When the tag releases from the animal and floats to the surface, we can navigate towards it and recover it — which is important, as these archival tags must be retrieved for their logged data to be downloaded.
After recovery, my long night began. First, we check the suction cups for any sign of sloughed skin that could be analyzed for DNA, diet composition, or paternity. Next, it’s bath time, to remove all remnants of corrosive salt water. The next step, and to me one of the most frightening, is to communicate with the tag to determine if it recorded anything. Phew — we have data. Then it’s time to settle down for many hours of data offloading, during which it’s always a good idea to periodically check on things. And at 2 a.m., with everyone asleep, there is little competition for bandwidth so it makes for a good time to check email.
Many hours later, the tags are finished offloading. After serial backups, it’s time to convert raw data to meaningful squiggly lines and .wav files. Success! Not only did we have two successful deployments and downloads, but also had a new record for the trip: one of the whales had dived to 1440m!
At 5 a.m., the next day is about to begin. Others will be up just before sunrise in search of new candidates to tag. As I hear folks heading to the galley for breakfast and coffee, I program the tags for their next outing, and grab a couple hours of sleep before mine.