Angler is on Channel Island filling cooler (9)
I believe the answer is:
fisherman
'angler' is the definition.
(thesaurus)
'is on channel island filling cooler' is the wordplay.
'on' says to put letters next to each other.
'channel island' becomes 'herm' (I've seen this before).
'filling' is an insertion indicator.
'cooler' becomes 'fan' (I've seen this before**).
'is'+'herm'='isherm'
'isherm' going into 'fan' is 'FISHERMAN'.
(Other definitions for fisherman that I've seen before include "He's an angler" , "Male anger" , "One possibly catching sole" , "He casts" , "Male angler" .)