Summarize the points made the lecture. Then, be sure to explain how they respond to the specific arguments presented in the reading passage.
Because a white orca is so unusual, some scientists have suggested that Iceberg, the whale seen off the coast of Russia, was the same animal as the orca seen earlier near Alaska. However, there are convincing arguments that Iceberg and the Alaskan white orca are actually two different individuals.
Slight Coloration Differences
First, although all the photographs made during the sightings show very light-colored animals, the orca seen in Alaska appears to be just slightly darker than Iceberg. Such differences in coloration suggest that these were two distinct animals that were independently sighted in the northern Pacific.
Sightings Far Apart
Second, the sightings were very far apart. The Alaskan orca was seen near the central Aleutian Islands, a long string of islands that extends westward from the mainland of Alaska. Iceberg was seen near the Commander Islands, off the coast of Russia. More than 1,500 kilometers separate the two locations. Typically, orcas tend to stay near the mainland coast and not travel such long distances.
Age Estimates
Third, when scientists saw the Alaskan white orca in 2000, they estimated that it was around twenty years old, based on the size of its dorsal (back) fin. When researchers saw Iceberg, their estimate of its age, based on the fin size, was also around twenty years but that was in 2010, when the Alaskan orca would have been thirty! The estimates again suggest quite strongly that these are two different individuals.
Narrator: Now, listen to part of a lecture on the topic you just read about.
Professor: Despite what the reading says, it’s perfectly possible that the white orca called iceberg by Russian scientists is in fact the same individual that was spotted earlier near Alaska. For one thing, the exact color of an orca’s skin can change a bit from season to season. The reason for this is algae. Algae are small plant organisms that grow on whale skin during some parts of the year. Algae growth would make white skin look a bit darker. The Alaskan sighting occurred during a different season than the Russian sighting, so if we take into account the seasonal variation in algae growth, it could have been the same whale seen both times, only one time it was covered with more algae than the other time.
Second, about the distant problem. It’s important to know that orcas live in groups that have different lifestyles. Some groups hunt mammals, while other groups hunt fish. The mammal-eating orcas tend to stay near coastlines and not migrate far, just like the reading say. However, scientists have determined that iceberg belongs to a fish hunting group. Fish-hunting orcas follow migrating fish and can travel over 2,000 kilometers in the open ocean. So it wouldn’t have been unusual for iceberg to travel between Alaska and Russia.
Third, age estimates based on the size of the dorsal fin are not necessarily accurate. You see, after an orca reaches twenty years of age, its dorsal fin doesn’t grow anymore so when scientists see an orca with a fully grown dorsal fin, that orca could be twenty years old, but it could also be twenty-five or thirty years old. So, iceberg could easily have been older than the scientists estimated, which means it could have been the same orca as the one seen in Alaska earlier.
