Sailor, solitary, will find shellfish (7)
I believe the answer is:
abalone
'shellfish' is the definition.
(abalone is a kind of shellfish)
'sailor solitary' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'solitary' becomes 'alone' (synonyms).
'ab'+'alone'='ABALONE'
'will find' acts as a link.
(Other definitions for abalone that I've seen before include "One lives in a shell" , "marine creature" , "Mollusc with an oval shell lined with bluish mother-of-pearl" , "paua" , "Sea food must be found" .)