Rows around galleon’s bow to listen for giant fish (5,5)
I believe the answer is:
tiger shark
'giant fish' is the definition.
'rows around galleon's bow to listen' is the wordplay.
'rows' becomes 'tiers' (tier is a kind of row).
'around' indicates putting letters inside.
'galleon's bow' becomes 'g' (I can't justify this - if you can you should believe this answer much more).
'to listen' becomes 'hark' (harking is a kind of listening).
'tiers' enclosing 'g' is 'tigers'.
'tigers'+'hark'='TIGER-SHARK'
'for' is the link.
(Other definitions for tiger shark that I've seen before include "big fish" , "Large aggressive fish" .)