These perhaps disturbed eelgrass catching prey finally (4,5)

'these' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'disturbed eelgrass catching prey finally' is the wordplay.
'disturbed' indicates anagramming the letters (the order of letters is disturbed).
'catching' indicates putting letters inside.
'finally' suggests the final letters.
The last letter of 'prey' is 'y'.
'eelgrass' with letters rearranged gives 'greseals'.
'greseals' placed around 'y' is 'GREY SEALS'.

'perhaps' acts as a link.

Can you help me to learn more?