Seal tagging part 2


Written by Mike Fedak.

After a long stretch of physical oceanographic work, on February 23rd, we got a suitable time window to once again try to catch seals and attach CTD-SRDLs. Our original plan was to tag roughly 8 elephant seals and 8 Weddell seals, but until the last few days we had only applied tags to 7 elephant seals. The ship has been totally occupied with physical oceanographic work. After completing work at the Thwaites Glacier front and recovering Autosub, we decided to once again try catching at the Edwards Islands.

Crew and Scientists aboard the JCR watch as the team on the ice tag seals

Unlike last time, this proved difficult. On the morning we were to set out in the rubber boats, it was cold (about -9 C) and the wind was strong, but the forecast was for improving conditions. This proved optimistic, to say the least, and by the time we were all on the water in the boats, the wind began to increase. But, having invested the time and energy of the crew and ourselves in getting that far, we headed into the wind for the islands, about 1 mile off. There was a steep and nasty chop. Imagine getting bounced around on some theme park ride while someone throws buckets of ice water (and I do mean buckets!) hard, into your face. It was a difficult situation to enjoy. But there was a brief highpoint as a passing leopard seal took an interest in the two boats and began swimming after us, surfing on the waves and pushing the first third of itself out of the water to have a good look at what it must have figured was an unusual potential foraging opportunity. But it soon gave up and we were left trying to avoid the worst of the spray. Each boat held four of us and the 3 passengers in each could at least get low down in the boat and turn our backs to the spray. No such luck for the driver who just has to take it full in the face.

We got into the lee of the islands where we had hoped for some protection from the worst of the wind. But the islands are low and almost seem to be streamlined with respect to the wind blowing off the ice fields of the continent. That is why they are relatively snow free. And the wind was rising rather than dropping, with gusts reaching 40 knots (force 8 gale). So we decided to give up and head back to the ship to see if conditions improved later. The ride back, going with the wind was relatively relaxing, although even waiting to get on board while the first boat was hoisted up to the deck was pretty miserable.

Conditions did not improve all day so the following morning we set off West across the Pine Island Bay over to the north of the Thwaites Glacier front where there was a large band of sea ice stretching northwest, which we hoped would provide good opportunities for catching Weddell seals. The weather improved, the wind dropped, the sun came out as the ship pushed into dense pack ice. We roamed the bridge, scanning with binoculars to locate the “right kind of seal”. Both Weddell and Crabeater seals are numerous in the pack ice. We were only interested in Weddell seals because of their benthic diving habit and their tendency to remain fairly local, as in other areas they have previously been tagged. Crabeaters were numerous but we also saw a few Weddells. We located one on a suitable floe and approached it with the ship.

From a seal’s perspective, a bright red, 7000 tonne ship pushing flows into one another pulling up next to yours with all the sound and vibration can’t be a very ordinary occurrence. I suspect that, were I that seal, I would be tempted to get in the water pretty sharpish. Yet, while showing signs of some concern and moving slowly away across the flow, the first seal we approached remained on the flow even after we were lowered onto the ice via the ship’s “Wor Geordie” (a netted platform that is lowered by the ship’s crane over the side). This may be because the seals have no land-based predators; the two main predators, leopard seals and killer whales take seals in the water. So if the seals feel threatened, they hesitate before entering the water.

Whatever the reason, three of us were easily able to surround the seal, keeping it on the flow. Then we darted it with the anesthetic and waited for it to become relaxed enough to glue the tag onto fur on its neck, just behind the head. We did not even have to clean and dry the fur. Unlike with the elephant seals who were lying on a filthy beach, the Weddell seal’s fur was clean and dry. The biggest problem was keeping the tag and epoxy warm enough so the glue would set properly. The entire process took just over 30 min. We waited until the seal was clearly alert enough to be left and then were winched aboard to look for another candidate.

A freshly tagged Weddell Seal.

By this time it was late afternoon and, moving off through very heavy pack, we soon saw an area with lots of hauled out seals, basking in what passes for warm sunshine down here (about -6 with light winds). We were able to tag 2 more seals before the Captain called time, and we went in for a late dinner, feeling that all captures would be this easy. This is not how it turned out.

We were up at local dawn the next morning, but the seals that had been present the previous evening were no longer on the ice. Indeed no seals were visible. And the weather had worsened. The wind was up to 35 knots and the temperature had dropped to -11C. The ship set off through the dense pack and we went back to searching the ice for seals.

In late morning, we located a seal and landed on the flow. We darted it easily enough but the air was bitterly cold and the wind was driving snow along the flow. We used a sledge to form a wind break to work behind and to protect us from the drifting snow. Everything seems more difficult in a strong wind. Our hands would go numb in moments after exposure, and thick gloves are not an option for the work of attaching the tags. The low temperatures slowed down the setting of the epoxy and it seemed a very long time before we were able to leave the seal and head off to the ship to search again.

Later in the day we spotted two more seals on a very large flow, the size of several football pitches. The captain drove the ship into the flow some distance from the seals. Once stopped, it looked like the ship was sitting in the middle of a broad snow covered field. Conditions were still the same and these animals had moved 100m or so away from the ship and were moving well away from the edge. Once lowered down we had a 100m sprint to the seals. Running full tilt through knee deep snow in full survival gear is hard work. Blowing hard, three of us managed to catch up with one of the seals while two others circled round the other and herded it slowly towards where we had settled to work on the first one. If anything, the wind was stronger and the air colder so, while the seals seemed un-phased by conditions, we found it difficult. But we managed to attach the two tags and get back to the ship. Several other candidate seals were in sight but given the time the crew spent out in the wind providing safety cover while we worked, the captain decided we should call it a day.

The following day, conditions were better and we had time to catch two more seals. One of these was still moulting so we could not tag it but we did catch and tag the second. That brings the number of tags we have applied to 14. We hope to get the chance to catch two more Weddell seals before we have to head back to Rothera to start our flights home.

The tagged animals have spread out in and around the Pine Island and Thwaites glacier area (see map), just as we had hoped. They have been diving to the sea bed in up to 1000 m of water sending back hundreds of CTD profiles. Whenever the animals surface to breathe, the locations, CTD profiles and diving behavior information is relayed via the Argos satellite to a database back in St Andrews where it is decoded, archived and available to the project online. We hope that the seals will continue to provide this data through the coming winter when we would otherwise have little information coming in. Of course the seals might have other ideas of where to spend the winter but we are betting they will continue to use the area of interest. Certainly, just now, the seals are diving and feeding where we hoped they would. We will keep our fingers crossed that they keep up the good work. One way or another, we will gain valuable info on the movements and foraging behaviour of these species, here at the limits of their range.


Map of seal tracks using tags deployed during this mission. Note that the ice distribution is from Google Earth and out of date!

Via: Ocean2ice blog

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