Yes, they're mostly common seals, and I believe the only area on the north-east coast where they breed.
As regards birds Seal Sands and the Tees Estuary is an Internationally important area for both numbers of sea birds and the number of species. Range of species vary throughout the year but with winter coming up some of the more special ones to watch out for are the Divers - Great Northern, Red-throated and Black Throated - they were here in good numbers last year and often giving very close views. Slavonian Grebe, Red-necked Grebe and Black-necked Grebe are regulars over winter from the Seal Sands hide. Grey Plover, Red-breasted Merganser and Golden Plover are usually in good numbers as well. At present Bar-tailed Godwit are increasing in numbers often giving close views. Twite are starting to arrive and a few Snow Bunting have been seen - they usually attract Merlin as well - there's one around at present down there. Various Geese species the more interesting ones include Barnacle, Bean and Pink-footed. For other birds of prey there's always Kestrel around and quite often Peregrine which breed locally. Short-eared Owls are often into double figures as well.
Other regulars are Dunlin, Sanderling, Purple Sandpiper, Knot, Curlew, Cormorant, Shag, Oystercatcher, Shelduck, Turnstone, Redshank, Teal, Wigeon etc.
All in all it's one of the best areas locally to see birds any time of the year, but especially October-May.