Beached without first emerging half-way for seafood (5-2-3)

'seafood' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'beached without first emerging half-way' is the wordplay.
'without' is a deletion indicator.
'first' becomes 'a'.
'emerging half way' becomes 'emer' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'beached' with 'a' taken out is 'beched'.
'beched'+'emer'='BECHE DE MER'

'for' is the link.

Can you help me to learn more?