Whales, seals and dolphins are regular visitors to Sydney Harbour, particularly between June and October. Whales have been known to beach themselves along the Sydney coastline and in the past people probably kept watch for these events as they enabled large numbers of people to gather and feast.

Dugong bones unearthed at Sheas Creek in St Peters in the 1880s, which have 'cut marks and scars' on their surface, suggest the animal was butchered probably for food.

Seal bones found in coastal shell middens suggest that these animals were probably hunted by Aboriginal people. The small amounts of seal bone recovered in the excavations, however, suggest seal was either not a major food item, or was butchered and/or eaten away from campsites. The bones are probably those of the Australian Fur Seal, Arctocephalus pusillus. Before the mid 1800s, when European hunting killed thousands of seals, numerous colonies extended along the New South Wales coast to just north of Newcastle.

The local name for one of the seals was Wan yea-waur and that for dolphin or 'porpoise' was Bar-ru-wall u-re.