The whale watchers soon noticed the tree was moving -- and that it wasn't a tree at all, but rather a buck swimming between islands.
"In Alaska and Northern B.C., transient orcas are known to prey upon deer and moose as they swim between islands or across inside passages," the tour company wrote in a Facebook post.
Malleson said he has heard of killer whales attacking deer and moose off the Alaskan coast, but no one has successfully documented such an incident.
"I was sort of excited to think I could be one of the first people to photo-document a hunt," he told CBC News.
Malleson's hopes were dashed, however, when the orcas passed by the deer without incident.
"Unfortunately, there was no predation," he said. "Well, fortunately for the deer ... but unfortunately for the photo-op."
Malleson said he decided to help the buck, which appeared exhausted from swimming, find its way back to shore. A video recorded aboard Malleson's boat shows the vessel guiding the buck toward a nearby shoreline.
"It felt good getting the buck back to safety," Malleson said. "He seemed pretty tired."
