Here's why:
* It depends on the context: Are they on a whale watching tour? On a research vessel? A fishing boat? The crewmember's reaction will vary depending on the situation.
* It depends on the crewmember: Some might be stoic, others might be excited. Some might have a specific call they use.
* It depends on the whale: Is it a small, familiar species or a rare giant?
Here are some possibilities:
* "Whale! Whale!" (Simple and excited)
* "There's a humpback!" (Specific to the species)
* "Blowhole! Get ready!" (If they are getting ready to photograph or study the whale)
* "Right there! Port side!" (Giving directions for the rest of the crew)
Let me know if you'd like to come up with a more specific scenario!