Protecting Waiau Toa/Clarence River’s Black-fronted Terns
The number of black-fronted tern chicks surviving to fledgling stage in the Waiau Toa/Clarence River has more than tripled since the start of a five-year protection programme.
In the 2017/18 breeding season, 162 birds at monitored sites along the Waiau Toa/Clarence and Acheron Rivers survived to fledgling (chick) stage. That compares to just 31 birds reaching that same stage in the 2015/16 season.
Black-fronted terns are ranked Nationally Endangered and the greatest decline in tern breeding populations has been on rivers classed as 'low-flow' such as the Waiau Toa/Clarence River.
While the overall predicted decline rate of black-fronted terns is around 50% over the next 30 years if nothing is done to protect them, that number is higher - around 90% - for populations nesting on these low-flow rivers.
The main issue is in part to the variety of predators they face (both ground and aerial), loss of breeding habitat to woody weeds, and the fact that they nest in small scattered colonies.
Five-year black-fronted tern protection programme
In 2015 Environment Canterbury, Department of Conservation and the Kaikōura Water Zone Committee committed more than $500,000 to a five-year black-fronted tern restoration project aimed at improving breeding success of the Waiau Toa/Clarence River population.
The project uses a combination of predator control, weed control and habitat enhancement around three breeding islands in an attempt to improve the breeding success of black-fronted terns.
This involved deepening channels around the three "managed" islands to lessen predator pressure. The islands were then scraped to remove all weeds, improving nesting habitat and removing cover for predators. Finally the islands were mounded up higher to lessen the risk of flooding.
Predator trapping also occurred around the managed islands.
Positive results to date
The average number of chicks per nest on both the managed and unmanaged black-fronted tern colonies has increased since the project began.
In the 2015/16 breeding season, only one chick per 10 nests monitored survived to fledgling stage on the managed colonies. In 2017/18, that number had risen to almost six chicks per 10 nests monitored.
In the unmanaged colonies, the average number of chicks per nest has increased from less than one chick per 10 nests in 2015/16 to about 2 chicks per 10 nests this season.
The project will continue for another two breeding seasons until 2020.