Ancestor drops net for ocean predators (5)

I believe the answer is:

orcas

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'predators' is the definition.
The definition and answer can be both animals as well as being plural nouns.
Perhaps they are linked in a way I don't understand?

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for orcas that I've seen before include "Killer whales" , "Killers" .)

I've seen this clue in the Irish Times and the Irish Times (Crosaire).

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