Seabirds are at greatest risk from discarded plastic in the seas around New Zealand, conservationists warn.
This is because New Zealand is home to so many threatened species, Forest & Bird said in a report presented to Parliament's Environment Committee today for Plastic Free July.
"Rubbish that ends up in our seas has a far worse effect on seabird species than anywhere else in the world," spokeswoman Karen Baird said.
"Even though we don't have the most plastic pollution, we have very high densities of seabirds in the Tasman Sea.
"New Zealand also has the highest number of threatened seabird species, many of which are found nowhere else in the world."
Describing the nation as the seabird capital of the world, Baird said 36 species breed only on New Zealand islands - as compared to just five species breeding in Mexico, the nation with the next highest number of endemic species.
In addition to being a breeding ground, New Zealand also served as a drop-in destination for a third of all seabird species in the world.
However, on local beaches, 78 per cent of all human waste is plastic, with most of it being fishing lines, plastic bags or small fragments, Forest & Bird said.
"Plastic rubbish is being fed to young birds by their parents, and it's killing them," Baird said.
"Until recently, the unfussy eating habits of birds like shearwaters and albatross were an evolutionary advantage.
"But now, when they are at sea looking for food to feed their chicks, they can't distinguish between floating plastic and fish."
Studies of some Australian shearwater colonies found nine out of every 10 fledglings had eaten considerable quantities of plastic, Baird said.
A new BBC documentary, Drowning in Plastic, also found shearwaters on remote Lord Howe Island were starving to death because their stomachs were so full of plastic they had no room for food.
Seabirds were also not the only animals at risk from plastic.
"One out of every three turtles recovered in New Zealand has died or is sick from eating plastic," Baird said.
She said floating plastic was also able to carry pests from other parts of the world, potentially bringing an economic threat to agricultural industries.
Plastic Free July was aimed at getting New Zealanders to reflect on whether they could cut down on their plastic use to help keep oceans safe for animals, she said.