Scientists from the Department of Conservation (DOC) and Deepwater Group (DWG) say GPS technology and remote cameras are helping them better understand how to prevent sea lion pups from dying on the subantarctic islands.
The rare New Zealand sea lion/rāpoka is listed as “Nationally Critical”, the highest risk classification. This season 1,792 pups were born at the main breeding ground in Auckland Islands, down slightly from last year’s count of 1,965. At the second most important breeding ground on Campbell Island 734 pups were born, an increase on the 696 counted during the previous survey in 2015.
DOC Science Advisor for Marine Species and Threats, Dr Laura Boren said, “Sea lions face a range of natural and human-related threats, such as disease, drowning and starvation from getting stuck in mud holes, being caught in fishing nets, environmental change, food availability and predation by sharks.
“Conservation staff, the seafood industry, and researchers are working tirelessly to find ways to prevent pups dying from disease and from falling in mud holes – the most significant risks for younger sea lions.”
She said fewer pups died this season than in previous years, which was encouraging. Mortality dropped from nine percent in 2017 to five percent at the Auckland Islands this year.
At Campbell Island, survey numbers indicate pup mortality was at 23 percent this year, a significant decrease from 58 percent in 2015 – the last time this population was monitored.
DOC and the seafood industry, through DWG, initiated a collaborative project on Campbell Island this year to better understand how to mitigate these threats, and believe they got some promising results.
DWG chief executive George Clement said, “While it is very encouraging that fewer pups died at Campbell Island this season, the loss of 170 pups this year (down from 404 in 2015), is still an unacceptably high number.
“Any way that we can minimise pup mortality will help the overall populations. It is essential we continue to monitor these populations and find ways to reduce the high numbers of pup deaths, which is why DWG is supporting this programme on Campbell Island,” said Clement.
It is the first time a team has been back down to monitor sea lions on Campbell Island since 2015, and through the New Zealand sea lion/rāpoka Threat Management Plan this population will be monitored and supported annually for at least the next five years.
The project has now set up cameras around mud holes and creeks to monitor the pup behaviour, and GPS technology is being used to track pups around the colony.
Boren explains, “This will help better identify what is causing these deaths and what could be done to prevent this, such as putting ramps in mud holes for pups to climb out on or by filling in the holes or creating barriers to prevent pups from falling in.”
It is thought that the unusually dry summer this year may have contributed to this year’s lower pup mortality.
Since arriving home, the team has been sharing what they have learned with a team heading down for a short trip in March for part two of the collaboration.
As part of the second stage, an engineer from Fulton Hogan will be sent to Campbell Island to provide recommendations on practical solutions for mitigating pup mortality from these holes, as well as DWG trialling the deployment of drones to assess their ability to monitor protected species on these remote islands. The goal is to test the feasibility of counting both sea lions and grey-headed albatross on Campbell Island, as well as producing aerial maps of the sea lion colonies.