At sea, punishes Klaus, on vacation, netting catch of fish (9)

'at sea punishes' is the definition.
I don't know anything about this answer so I cannot judge whether this works.

'klaus on vacation netting catch of fish' is the wordplay.
'on vacation' suggests removing the centre (after the inside letters have vacated the word).
'netting' indicates putting letters inside (net can mean to contain or capture).
'catch' becomes 'eel' (potentially makes up a fisherman's catch).
'of fish' becomes 'haul' (I can't justify this - if you can you should believe this answer much more).
'klaus' with its middle removed is 'ks'.
'eel'+'haul'='eelhaul'
'ks' placed around 'eelhaul' is 'KEELHAULS'.

Can you help me to learn more?