Island also claiming catch (6)
I believe the answer is:
tobago
'island' is the definition.
(Caribbean island)
'also claiming catch' is the wordplay.
'also' becomes 'too' (synonyms).
'claiming' indicates putting letters inside.
'catch' becomes 'bag' (bagging is a kind of catching).
'too' placed around 'bag' is 'TOBAGO'.
(Other definitions for tobago that I've seen before include "Island paired with Trinidad" , "island location" , "West Indian island" , "Trinidad and - (WI)" , "Trinidad companion island" .)