Thalassa Kawachi talks to Auckland Point School pupils about marine biology on the Haulashore Island Ferry.

Haulashore Island was invaded by 85 happy little pirates this week when Auckland Point School pupils plundered the island's trash and treasures.

Four boatloads of people, which included around 30 parents and teachers, spent a pirate-themed day learning about the area's environment and history.

Before a harbour cruise for six lucky children and a lolly scramble for the rest, pupils collected rubbish and scoured the beach for natural treasures, with fossilised scallops and a head-sized whale vertebrae among the most exciting finds.

Glenn Bisdee Nelson's Auckland Point School pupils and caregivers enjoy a day out to Haulashore Island.

School parent Glen Bisdee and wife Thalassa Kawachi helped fund and organise the day. Bisdee said some finds reinforced the importance of being a tidy Kiwi.

"Some of the kids found a birds nest that was just marred by plastic.

"Once we got back to the area where the groups had scrounged, we attempted to identify the items. Then we had a talk about the rubbish and how that got there."

Kawachi, a marine biologist, then spoke to the children about throwing away rubbish "so it doesn't end up in the stormwater drains," Bisdee said.

Principal Sonya Hockley said Auckland Point was an "enviro-school", and was pleased to contribute to the preservation of the island.

Part of a $2,000 fund-raising effort by the PTA at a recent open day was set aside for the trip after a 2013 visit to the island proved popular, Hockley said.

"The PTA raised some money towards the cost of it and Glen and Thalassa donated some money towards that as well.

"[Glen] is very much involved [with the school] and he wants to support what we do. He's very enthusiastic about his charity work and we support him in that."

Bisdee donated 84 fleeces to Auckland Point School students in July through his charity Keeping Kids Warm.

He said some of the school's students had never been on a boat before and that covering the funding shortfall for the pirate day gave them an opportunity to learn on the ground.

"For some of these kids some activities aren't going to be that comprehensive so getting them outside is a good start.

"At the end of it everyone was pretty shattered, but I think they got a lot out of it."