Pack of whales

A group of sexually generous females with whom one is likely to be able to enjoy sexy times.

"Oi oi, look sharp lads."
"Who even says that?"
"Never mind about that, Jeremy, we appear to have stumbled across a pack of whales!"
"Oh good! No doubt they'll have sex with us."

Hit a pack of whales

To come across a group of the kind of easy girls, and to have lots of sex with them.

"Hey, bro, look over there."
"Where?"
"Over there by the tree."
"Oh shit, we've hit a pack of whales! I imagine we'll have loads of sex."