Anti-whaling outfit Sea Shepherd is joining the effort to save the endangered Hector’s dolphins, in the South Island.

Spokesman Michael Lawry says the population has declined by over 80 percent in the past 50 years.

Numbers are down to about eight thousand, and he says Sea Shepherd can help by protecting the animals' habitat.

"We're going to be looking for any of these illegal operating fishing vessels. Obviously something has been killing our dolphins for the last 50 years, some of it has been illegal recreational set nets and some of it has been illegal inshore fisheries."

Lawry says the decline in the Hector’s dolphin population and reports of them being caught in set nets is worrying.

"So we're going to be out there in an effort to reduce the risk to Hector's from any illegal unregulated and unreported commercial or recreational fishing, and the first phase is going to be from Te Waiwai Bay up into the Canterbury Bite."