A danger to other remaining creatures at sea, initially? (5)

I believe the answer is:

orcas

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'a danger to' is the definition.
I can't tell whether this definition defines the answer.

'other remaining creatures at sea initially?' is the wordplay.
'initially?' says to take the initial letters (I've seen 'initially' mean this).
The first letters of 'other remaining creatures at sea' is 'ORCAS'.

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 Independent.

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