Vessel catching sole at sea for bulk trader (10)
I believe the answer is:
wholesaler
'bulk trader' is the definition.
(someone trading items in bulk)
'vessel catching sole at sea' is the wordplay.
'vessel' becomes 'whaler' (whaler is a kind of vessel).
'catching' is an insertion indicator.
'at sea' indicates an anagram.
'sole' anagrammed gives 'oles'.
'whaler' enclosing 'oles' is 'WHOLESALER'.
'for' acts as a link.
(Other definitions for wholesaler that I've seen before include "Supplier to the trade" , "One supplying retailers in bulk" , "firm that supplies in bulk" , "Merchant" , "Retailer's supplier" .)