A low hum started up from the top deck of the R/V Norseman II, and quickly became a loud buzz not unlike the sound of a swarm of angry bees. The four small propellers on our UAS (unmanned aerial system) spun up to speed and our drone was launched. As it rose to 200 feet, the sound became a faraway buzz and pretty soon we couldn't hear it at all. Our target was a seal somewhere out in a thick band of densely packed ice. At the time of this survey (Monday April 22), persistent easterly winds had compacted most of the free moving ice floes into larger combined sheets. We determined that the seals were likely to be resting in the middle of these bands, on floes inaccessible to our smaller inflatable boats, so we used this opportunity to survey them with our drones.
Before we commit to a UAS flight, we need to find a suitable seal target. We packed five researchers into the bird box, a small outdoor viewing platform above the bridge of the R/V Norseman II. Dressed in mustang survival suits and equipped with binoculars and a spotting scope, we scoured the ice for anything resembling a seal. After half an hour of searching floes, Josh London, Alaska Fisheries Science Center marine mammal biologist, pointed out the first animal of the day. Its large round silhouette contrasted nicely with the sharp edges of ice that surround it. However, this thing was big…suspiciously big. We saw two long flashes of white tusks rise up from the animal before it rolled back over and into the water. Our first Walrus sighting of the trip! It’s always a treat to see these enormous animals, but we were after one of the four ice-associated phocid seals, ribbon, spotted, bearded or ringed.
Our efforts did not go unrewarded though. Soon after we had a ribbon seal in our sights. We radioed down to the flight team and they began the preflight checklist. After ensuring that our drone was fully operational and ready to fly, one of the team held the drone above her head while the rotors were fired up and the drone was launched. A spotter guided the drone to the target until it was visible to the pilot through the drone’s camera. Fitted with a laser rangefinder (LRF), a high resolution color camera, and a thermal imager, these drones enable us to take overhead images of seals without disturbing them. The LRF gives us information about the altitude of the drone, which is used in determining the size of each animal. We can then estimate the body condition (how fat, healthy they are) in ice seals and track their health trends over time.
Over the course of the trip, we successfully flew over dozens of ice seals. There were several instances where more than one seal was present on an ice floe. Many times this was just a mom and pup pair, but occasionally we found “triads” of spotted seals comprised of a female, her pup, and a male suitor. These groupings are commonly seen during the pupping, nursing and breeding periods, but only among spotted seals.
We collected thousands of UAS images of seals, and the process of carefully measuring seals will begin over the next few months, when the busy summer field season comes to a close.
