17 April, 2000

Dive at Christine Island; Penguins

Question 58: What are "baleen whales"?

Today turned out to be a lovely day with sun peeking through beautiful, puffy white clouds. We started off at 9 am for a three-person dive (myself, Katrin Iken, and Bill Baker) at Christine Island. When we got to the rock wall near the dive site at the north side of the island, there were Gentoo Penguins romping in the water. They continued diving around the area while we got ready for our dive in the boat. But when we finally got into the water, they seemed to have disappeared. We started our descent without them.

At about 20 feet, Bill pointed up to the water above us and there they were! Ten to fifteen Gentoo Penguins spiraling through the water like little torpedoes! With the occasional rays of sun spiking down through the water, it was an unearthly scene. At around 60 feet, one of the penguins slowed down and swam right towards me, stopping 4 feet away for a few seconds before zooming off again. They scarcely seem to have to put any energy into their graceful, speedy "flight". All around us, they performed their three-dimensional water ballet for almost 10 minutes and down to 120 feet. It was a mesmerizing sight, so rare that none of us wanted to look towards the bottom, abandon the penguin watch and start to collect invertebrates and algae.

There are three species of penguins that breed in the vicinity of Palmer Station: Gentoos, Chinstraps, and Adelies. We saw many Gentoos and Adelies, the Chinstraps less frequently. The Gentoos are the largest at 80 cm in height. Chinstraps and Adelies are similar in size at 60-65 cm. In all three species there is little sexual dimorphism (the females and males have identically colored and marked plumage). The breeding season was over, and all the chicks had fledged and departed into the ocean by the time we arrived here. The penguins that remain on the islands in the area are adults who are molting into their new feathers for the year.

The major part of the populations of both Chinstraps and Gentoos have historically nested further north in the subantarctic islands, but over the last 25 years of warming conditions, their ranges have expanded further south. The nesting colonies of Adelie Penguins, which range from the Antarctic Peninsula all the way south to Ross Island, have decreased in size in the peninsula area over the same time period. Previously, 15,000 pairs of Adelies nested within two miles of Palmer Station. Analysis of the nesting areas shows that Adelies have been the most common penguin here for at least the last 600 years. They are still the most common penguin here today, although the same colonies around Palmer now have only 7,700 nesting pairs. Scientists looking for the cause of this change have found a decrease in young krill (a major part of the Adelie's diet) in the area. Fewer winters over the past decades have created the extensive sea ice needed to properly shelter young krill. In the winter Adelies feed by the ice edge, while Chinstraps and Gentoos feed in open water. The warming air also holds more moisture, bringing more snow. Adelie pairs mate for life and stick to the same nesting site every year no matter what. Even when that area is covered in snow, Adelie pairs will stubbornly try to nest at their site, piling stones on the snow and eventually losing eggs and chicks to freezing meltwater. Chinstraps appear to be more flexible and choose a nest site based on its current suitability.

This does not spell the end of Adelie Penguins. Between the movement of their winter feeding grounds and the decreased quality of their traditional northern nesting sites, the population of Adelies seems to be moving south. The same conditions that are making the northern parts of their range less successful are improving the conditions in the southern parts of their range where their nesting numbers are increasing.

Answer 57: The Antarctic Tern appears similar to our Arctic Tern, but it does not migrate north out of the Southern Ocean. It feeds on Antarctic silverfish and krill in summer and at the edge of the pack ice in winter. The Arctic Tern does migrate south and is found in the Southern Ocean in the southern summer/northern winter.