Knowledge added to collection of animals after hauling up sea-monster (6)
I believe the answer is:
kraken
'monster' is the definition.
(I've seen this before)
'knowledge added to collection of animals' is the wordplay.
'knowledge' becomes 'ken' (ken is a kind of knowledge).
'added to' is a charade indicator (letters next to each other).
'collection of animals' becomes 'kra' (I can't justify this - if you can you should give a lot more credence to this answer).
'ken' after 'kra' is 'KRAKEN'.
'after hauling up sea' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for kraken that I've seen before include "Legendary monster of Norwegian seas" , "Sea monster that sleepeth (Tennyson)" , "A legendary sea monster of Norwegian myth" , "Mythical sea monster (Norway)" , "Mythical sea-monster off Norway's coast" .)