As sea lions become an increasingly common sight on Dunedin beaches, new research is helping advocates for the species tell an important story. From Southland up to Northland, New Zealand’s entire coastline is sea lion habitat. The massive marine mammals belong here and people should plan for their return. Hamish MacLean reports.
From North Cape south, New Zealand’s mainland was once teeming with sea lions.
When humans arrived, that all changed.
New Zealand sea lions were hunted relentlessly and wiped from the map.
The endemic animals were driven into a refuge in the Auckland Islands, where sealers’ wooden boats could not venture, and only recently has the now nationally vulnerable species returned to the mainland.
In the beginning, a single female, Mum, arrived in Dunedin in the 1990s, and she had a pup.
Now, conservationists are hopeful a growing population of her descendants breeding along the city’s coast could signal the beginning of the species reclaiming their former breeding grounds.
Exactly when and where they might be found in future remains unknown, but an American PhD student, who has never seen a New Zealand sea lion in the wild, has developed a tool expected to be used to predict and plan for their return to the coasts of both the North and South Islands.
Help from abroad
Veronica Frans is an ecologist and a PhD student at Michigan State University who developed an interactive map, now hosted on the Department of Conservation (Doc) website, using something called an "integrated species distribution model database".
The database she created not only makes the map easier to interpret, it also allows for additional evaluations for decision-making and conservation action, she said.
Using data collected through previous research in breeding colonies in the Auckland Islands, Ms Frans was first able to create a model of "habitat preference" for the species and overlay that model on to a map of the mainland.
The map showed sites that would be suitable for sea lions to again establish breeding colonies along the coast.
The assessment identified 395 sites along the coasts of both the North and South Islands where colonies of 35 or more females could settle.
Ms Frans, whose master’s research focused on the species and who has studied at Lincoln University, said it was a sign of hope for the species’ recovery.
"We never imagined 395!" Ms Frans said via email.
"It was definitely a surprise to us."
The database she created was produced after conversations with Doc rangers, decision-makers and sea lion experts, so as to refine the initial modelling.
The overlapping assessments it allowed showed that the actual suitability of 90% of the 395 potential breeding colony sites was questionable because of human activity.
More than half of them contained human-made barriers such as fences or pasture, and three-quarters had roads nearby.
Further, only 5% of the predicted colony sites were in protected areas.
But the main thing it displayed was the potential for the New Zealand sea lion to one day be found all over the country, she said.
"One day, I really hope to see one," she said.
"It would be a dream after studying them for so long.
"For now, I do what I can from a distance, using data that others have collected on the ground, and am happy to help where I can."
Here and there, a difference
Here in New Zealand, WildCoastNZ environmental consultant Amelie Auge said the map Ms Frans created highlighted the need to educate New Zealanders that the large mammals belong here, so "get used to it".
It was Dr Auge’s GPS tracking work that was used by Ms Frans to build the map.
Dr Auge said sea lions’ behaviour in Otago was markedly different from the Auckland Island population.
In the Auckland Island subantarctic population centre, harems of females gathered and were protected by a dominant male.
The breeding season here was marked by single mothers stealing away to have their pups in peace, safe from overzealous males and other dangers.
The accepted thinking here was that once numbers increased on the mainland, sea lions would reach a "critical mass", and their behaviour would change.
"The accepted idea — and we’ll have to see if it’s right — is that when there’s more females here, the idea is that they will start forming those breeding aggregations [harems].
"It’s just that at the moment there is not enough of them for them to benefit from gathering, because they gather basically to protect [themselves] from other males and stuff.".
However, another change might be more noticeable, Dr Auge said.
Sea lions could also reach a critical mass on the mainland and, after years of slow growth, the population could then undergo "exponential growth".
"If it happens ... you think there’s a lot at the moment, potentially you could have a lot more."
Few people know Dunedin’s small population of sea lions as well as Doc biodiversity ranger Jim Fyfe.
He said it would likely take 10-15 years of growth before Dunedin could properly say it had a sea lion "population" around the city.
The technical definition of a colony is a site where females have produced 35 pups a year for five consecutive years; last year Dunedin’s sea lions produced a record 22 pups.
And yet the animals have already become a common sight at city beaches.
Surfers at St Clair are learning to co-exist with them with different degrees of success, and every summer Doc rangers and others have to do work from Warrington to Brighton as sea lions and people meet at the beach.
"Imagine if we were having 100 pups being born," Mr Fyfe said.
"Now that they’re coming back, we are having to re-learn our relationship with them."
A refuge, and a second chance
The species’ stronghold, where around two-thirds of all New Zealand sea lion pups were born, was Dundas Island, in the Auckland Islands archipelago, Mr Fyfe said.
It was roughly the size of a couple of rugby fields, but its sandy shelf was completely surrounded by rocky reefs, which once kept sealers’ boats at bay.
From this refuge, sea lions would travel nearly 100km to foraging grounds and would dive regularly to 200m to find food.
Off Otago Peninsula, the fishing was much closer.
Whereas it was not unusual for Auckland Island sea lions to head out on a three-day trip to forage for food, here the animals swam a few kilometres, dove down to 20m for a feed, and were "home by lunchtime", Mr Fyfe said.
Ms Frans’ map showed how extensive sea lion habitat was around New Zealand’s coast, he said.
It highlighted that pups were found in middens all the way up in North Cape.
However, what it really promised was a tool for people planning for coastal infrastructure or sea-level rise to take into account where sea lions might be found one day.
In terms of district councils or regional councils creating plans for the future of their coasts, taking into account sea lion habitat would be important, he said.
"We’ve got sea lions here and they’re voting with their flippers," he said.
"Female sea lions - and they’re the ones we are really worried about because they’re the ones that produce pups and keep the species going — they need choice."
Otakou head Edward Ellison said there was evidence of sea lions once populating the area in good numbers.
There were various accounts of chiefs or ancestors having encounters with sea lions up and down the coast, he said.
There were place names that might relate to sea lions, as well.
"They were obviously quite prolific in number and there were encounters," Mr Ellison said.
"There were a few accounts of bravery, I suppose.
"They were also hunted, obviously, because they’re big beasts and they may have had bones that were of use besides the meat.
"I think it’s a good sign that they are resuming their place."
