Master of fishing vessel we’re told? (4)

I believe the answer is:

erne

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'master' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

I can't explain the remainder of the clue.

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(Other definitions for erne that I've seen before include "Marine flyer" , "Eagle, river and lough" , "bird of prey" , "River and lake of the North" , "Seabird" .)

I've seen this clue in The Times.

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