Entrance of the Whales
Today we made a flight by helo along the fast ice edge and into the ice channel being made by the Oden, a Swedish icebreaker. Our purpose was to find out how many whales are in the vicinity. We found in previous years that when lots of whales arrive in the penguins’ foraging area, then the penguins’ feeding trips get longer and they switch from krill to fish. Therefore, it was clear that the whales and penguins were competing for food. Both the penguins and the whales feed along the fast ice edge, because as it breaks out, schools of fish and krill, which ‘hide’ way under the ice beyond these predators’ breath-holding range, become exposed to predation.
Keeping track of the whales was easy at Cape Royds in 2001-2005, because the fast ice edge never went south of Royds. Thus, the whales — both minke whales, which eat krill and fish, and ‘ecotype C’ killer whales, which eat fish — were easy to keep track of just by sitting at a high vantage point with binoculars and spotting scope. Last season, though, the fast ice edge eroded south to the point that we no longer could see it; it was open water from Royds to the ice, several kilometers to the south. So, the whales were beyond view.
Last season, 2006-07, we noticed a dramatic exodus of adults from Royds on the 15th of January (see figure below). My suspicion was that a bunch of whales had arrived. So, this year we’ve been making helo flights along the ice edge to do a whale census about once a week. On 4 January, we saw just 6 minke whales (MW) and 6 killer whales (KW), and during that period the penguins were making short foraging trips. Lots of adults hung around in the colony. When we made the flight today, we encountered an astounding 73 minke whales and 32 killer whales in the same areas as the 4th Jan flight. On this day, too, there was a mass exodus of adults. The helo pilot reported that in the previous few days he’d seen just a few whales present.
It seems fairly clear, then, that the whales are causing the penguins to work harder. Why so many are present in McMurdo Sound this season, we don’t know.
When both parents of chicks leave the colony to forage, the chicks gather in groups, called ‘creches’. The adults who remain keep the skuas at bay. In years previous to 2006, Royds parents never made long foraging trips and, thus, many hung around. Chicks never made crèches. This season, though, there are lots of crèches. However, in spite of this, the chicks’ growth rate is actually a bit higher than last season; and last seasons’ rate was typically high, compared to what we find at other colonies in the region. Thus, by having the chicks form crèches, allowing both parents to forage simultaneously, the Royds penguins are keeping up with the whales. You see, they’ve been working this out for millennia.