Yes, SHELDRAKES is a Scrabble word!

Letter values in Scrabble US: S 1, H 4, E 1, L 1, D 2, R 1, A 1, K 5, E 1, S 1.

Is it a valid word?

SHELDRAKES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

large crested fish-eating diving duck having a slender hooked bill with serrated edges
Old World gooselike duck slightly larger than a mallard with variegated mostly black-and-white plumage and a red bill

Also: fish duck.