Stick around old dock, primarily to find swimmer (7)
I believe the answer is:
codling
'swimmer' is the definition.
(codling is a kind of fish)
'stick around old dock primarily' is the wordplay.
'stick' becomes 'cling' ('cling' can be a synonym of 'stick'**).
'around' indicates putting letters inside.
'primarily' says to take the initial letters.
The first letters of 'old dock' is 'od'.
'cling' enclosing 'od' is 'CODLING'.
'to find' acts as a link.
(Other definitions for codling that I've seen before include "Two fish combine to make a young one" , "kind of apple" , "Immature fish" , "little one underwater?" , "Small fish" .)