An orca pod has been harassing and killing porpoises for decades — but they don't eat them. Scientists still don't know why.

• Researchers found that a certain group of orcas are killing porpoises for an unknown purpose.
• The orcas could be doing it just for fun or to teach hunting skills to younger members of the pod.
• The orcas may also be "mismothering" the porpoises given limited opportunity to raise their own young.

Researchers have been watching a group of orcas in the Pacific Northwest harass and kill porpoises for nearly 60 years. But oddly enough, the killer whales don't eat the animals.

So why spend all that time and effort?