What is the hardest prey to catch for a killer whale?

The hardest prey for a killer whale, or orca, to catch is often large, agile marine animals such as the elusive and fast-moving bluefin tuna or the highly acrobatic seals and sea lions. These prey species possess remarkable swimming speeds, agility, and the ability to utilize complex behaviors for evasion. Additionally, prey that dwell in deep or murky waters can also pose significant challenges, as orcas rely on echolocation to locate them. Ultimately, the difficulty can vary depending on the orca's hunting techniques and the environment in which they hunt.