Jaws of whale possibly catching swimmer back in seaside town (5,8)
I believe the answer is:
great yarmouth
'seaside town' is the definition.
The definition suggests a singular noun which matches the answer.
'jaws of whale possibly catching swimmer back' is the wordplay.
'jaws of whale possibly' becomes 'great mouth' (a large mouth).
'catching' means one lot of letters goes inside another.
'swimmer' becomes 'ray' (ray is a type of fish).
'back' says the letters should be written in reverse.
'ray' in reverse letter order is 'yar'.
'greatmouth' enclosing 'yar' is 'GREAT YARMOUTH'.
'in' is the link.
(Another definition for great yarmouth that I've seen is " Norfolk seaside resort".)