The Ports of Auckland says the number of Bryde's whales dying after being struck by ships in the Hauraki Gulf has dropped by three-quarters.
In September 2013, a voluntary protocol was brought in, asking ships to slow down and be more aware of the whales.
The port operator said prior to the protocol, research showed an average of two Bryde's whales a year died after being hit by ships.
But it said in the last two years, only one had been confirmed as dying from ship strike.
The protocol asked that ships travel as close to 10 knots as they can, use recommended approach routes into the port, and avoid whales when they see them.
Average speeds have since dropped from 14.2 knots to 10.9 knots.
The Ports of Auckland said it was too early to celebrate but it showed good progress in getting ships to slow down.