The death of two Hector's dolphins in set nets near Christchurch yesterday is a warning for the Government to step up their protection for this endangered species, the Green Party said today.

"The gruesome finding of two highly endangered Hector's dolphins in a fishing net highlights the fragility of this species," said Green Party oceans spokesperson Gareth Hughes.

Ministry of Agriculture and Forestry officials have said the incident appears to be the result of illegal fishing activity because the use of set nets is banned out to four nautical miles. Mr Hughes questioned the strength of this conclusion given numerous Hector's sightings outside the set net ban.

"Hector's dolphins have been seen by Ministry of Fisheries observers outside the set net ban area off the coast of the South Island, and independent academic research backs up these observations," said Mr Hughes.

"Whether the death of the two dolphins in a set net was the result of illegal or legal fishing activities, the Government should move to offer this endangered species more protection.

"The Government can act immediately to extend the set net ban further offshore to cover the areas in which Hector's dolphins are known to swim.

"The Government can also monitor the set net bans more thoroughly. Historically, monitoring has been poor.

"The set net ban doesn't protect dolphins if the ban is not enforced.

Mr Hughes said the Government could increase the aerial monitoring of the set net ban area, as well as increase the amount of Ministry of Fisheries observers on commercial fishing boats outside the set net ban.

"How many endangered dolphins need to die before the Government strengthens protection for them?" said Mr Hughes.