Organising fishing, gutted after young salmon head off (9)
I believe the answer is:
arranging
'organising' is the definition.
'fishing gutted after young salmon head off' is the wordplay.
'fishing' becomes 'angling' (angling is a kind of fishing).
'gutted' suggests removing the centre (to gut something is to remove its insides).
'after' means one lot of letters go next to another.
'young salmon' becomes 'parr' (I've seen this before).
'head off' means to remove the first letter.
'angling' with its middle taken out is 'anging'.
'parr' with its initial letter taken off is 'arr'.
'anging' put after 'arr' is 'ARRANGING'.
(Another definition for arranging that I've seen is " Putting into order or setting up".)