A sea lion had a spear embedded in its chest in a series of attacks on protected wildlife in the south that are worrying authorities.

The sea lion was spotted last Friday in Surat Bay, on the South Otago coast, with the Hawaiian sling diving spear lodged in its body.

By the time a Department of Conservation officer arrived to help the animal, it had fled.

"From pictures sent by the tourists who found the sea lion, it appears the spear was not deeply embedded and we hope it will dislodge by itself.

"If the animal is found, we will try to extract the spear and, if necessary, the animal will be netted and sedated," said DoC ranger Cheryl Pullar.

On Friday members of the public also reported a second sea lion with large cuts on a beach between Kaka Point and the Nuggets. The cuts did not appear to be naturally-inflicted.

These attacks follow last week's jailing of Southland man Harley David McKenzie for viciously attacking a leopard seal.

In other incidents at the weekend in the same region, a nesting yellow-eyed penguin was mauled by two dogs at Jack's Bay. It died, and its chicks were expected to die as well.

Before the attack, the dog owners were warned by locals that penguins were nesting and to keep their dogs away. There was also a sign on the beach warning of nesting penguins.

DoC received another report on Saturday of a rottweiler belonging to some youths harassing yellow-eyed penguins on the beach at Roaring Bay.

Coastal Otago area manager Robin Thomas condemned the "thoughtless acts of cruelty" by the people and dogs who killed, injured and harassed protected and endangered wildlife.

"These actions are not only totally illegal and seriously impact the species but, in respect of the sea lion incidents, are also potentially very dangerous," Mr Thomas said.

Sea lions were inquisitive, and especially so when encountering divers, but they would usually watch the activity for a while then leave.