15 April, 2000

Underwater Dangers 1

Question 56: What is a "tube-nose"?

One concern in Antarctic diving is the possibility of aggressive or potentially dangerous marine life. Since there are no sharks in the Antarctic, we worry about mammals. Seals and Orcas (Killer Whales) are the only animals here large enough to pose a risk. Common sense rules our interactions with them.

While all of the seals in this area are larger than we are, the only one that is truly predatory is the Leopard Seal. Although they have attacked humans on the surface and have behaved aggressively towards divers, no divers have ever been injured by Leopard Seals. We scan the dive site before the divers get in the water, and tenders keep watch at the surface while the divers are underwater. If a Leopard Seal is seen in the area, we abort the dive. The same procedure holds if one of the divers spots a Leopard Seal underwater. As soon as one is seen in the area, the dive is over.

The divers then ascend slowly to the surface and get out of the water as quickly as possible. Depending on the dive site, they may crawl out on shore or go directly back to the boat. As with bear interactions in Alaska, running away is avoided to keep from acting like prey. If a Leopard Seal gets aggressive with divers underwater, the divers can put their collecting bags and other gear between themselves and the seal. Members of our science group have seen Leopard Seals underwater on two dives; tenders have spotted leopards in the area and pulled the divers out of the water on two other occasions. The rest of the times Leopard Seals have been in the area, we have seen them before the dive started.

These seals have been a parcticular problem at Janus Island. This was the island where a lep approached a pair of divers at 80 feet and followed them to the surface on our first dive there (journal 3/14). Every time we went there after that, a lep showed up cruising the area shortly after the boat arrived at the dive site. Yesterday, we finally got to dive there again! It is a beautiful wall that drops over 500 feet. We went to 130 ft and found fabulous sponges, octocorals, anemones, nudibranchs, and one pencil urchin.

We have never seen any Orcas but the procedure is the same as for Leopard Seal sightings--we do not dive if they are seen nearby. Antarctic Fur Seals can be aggressive in the water during breeding season (October - February), but the rest of the seals are generally only curious underwater. If we were diving through holes in sea ice, we would have to watch out for Weddell Seals surfacing in our holes to breathe. They can be very aggressive in defending their air supply, and the males will bite during breeding season to protect their territory.

Another danger is the loss of your dive buddy. This occurs most often in low visibility conditions. We dive in buddy pairs to increase the safety and efficiency of the dive. The dive buddies should always be in sight of one another. If we lose sight of our buddy we take one minute to stop swimming and circle slowly off the bottom, looking for bubbles or disturbed sediment that would indicate a diver's presence. If we do not reconnect after the minute of circling, we resurface. Once the buddies reconnect at the surface, they can go back underwater and complete the dive if they were on a shallow dive and have enough air left.

Continued 4/16/00...

Answer 55: The edges of their upper and lower mandibles have serrations that help to strain krill from the water. When they feed, they patter with their feet over the surface of the water and scoop up mouthfuls of water from which the food is filtered. They also do shallow surface dives.