Wildlife authorities are investigating the theft of a jawbone from a whale carcass washed up at Phillip Island.

A sperm whale carcass more than 16 metres in length washed up at Forrest Caves beach last Saturday.

Authorities discovered on Friday morning that parts of the whale’s jaw had been taken from the carcass.

People are not allowed to come within 300 metres of the whale and a fence has been set up around the site.

The whale is being left on the beach to decompose naturally because authorities cannot access the beach with machinery or vehicles.

In other strandings, alternate disposal methods have been tried, but with little success.

In 1970, for instance, US authorities in Washington State thought it would be a good idea to surround a carcass with dynamite and blow it up. The resulting footage of the debacle has since become one of YouTube’s most viewed clips.

People have been told to avoid the area between Surf Beach and Woolamai Beach, extending 500 metres out to sea, due to the chance of sharks in the area.

Anyone who sees a shark is being advised to report the sighting by calling triple zero or alerting lifesavers.

Whales are protected under the wildlife act even when they are dead.

-with AAP