Boatman catches a crab — strangely shocking (7)
I believe the answer is:
macabre
'shocking' is the definition.
(thesaurus)
'boatman catches a crab strangely' is the wordplay.
'boatman' becomes 'me' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'catches' means one lot of letters goes inside another.
'strangely' indicates anagramming the letters.
'a'+'crab'='acrab'
'acrab' anagrammed gives 'acabr'.
'me' going around 'acabr' is 'MACABRE'.
(Other definitions for macabre that I've seen before include "Dark and disturbing" , "Morbidly repellent" , "Gruesome, suggesting death" , "Grotesque" , "Ghastly, gruesome" .)