Cod scare marine predator in Cornish river inlet (5,5)

I believe the answer is:

false alarm

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'cod scare marine' is the definition.
The definition suggests a singular noun which matches the answer.

'predator in cornish river inlet' is the wordplay.
'predator' becomes 'seal' (I am not sure about this - if you are sure you should believe this answer much more).
'in' is an insertion indicator.
'cornish river' becomes 'fal' (River Fal in Cornwall).
'inlet' becomes 'arm' (I've seen this in another clue).
'fal'+'arm'='falarm'
'seal' inserted within 'falarm' is 'FALSE ALARM'.

Can you help me to learn more?

(Other definitions for false alarm that I've seen before include "unfounded scare?" , "Warning proving unnecessary" , "Panic over" .)

I've seen this clue in The Independent.

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