For a long time New Zealand sea lions were only found on a few smaller islands, centuries of intensive hunting have brought them to the brink of extinction. In the meantime, however, some seals are returning to the coasts of the main islands. With the help of a new model, researchers have determined where there are suitable rearing sites for the seals and what influence roads, pastures and other anthropogenic structures have.
The New Zealand sea lions (Phocarctos hookeri) are among the most endangered large robes in the world. The sea lions, up to 3.50 meters long and weighing almost half a ton, were once common in the cool seas around New Zealand, but were then extremely decimated by intensive hunting. Today 95 percent of the just under 10,000 specimens are found in only three breeding areas on some of the subarctic islands south of New Zealand.
Raising boys in the forest instead of on the beach
One of the reasons for the sharp decline in New Zealand sea lions, in addition to hunting, is the rather unusual behavior of the females: They are the only species of sea lions that give birth to their young on the beach, but then migrate up to two kilometers inland with the offspring. There they prefer to raise the young in forests, where they are protected from wind, storms and aggressive young males. At the same time, however, this behavior exposes the animals to interference from human influences.
Wherever sea lion breeding areas and populated coastal strips overlap, encounters with potential risks for both sides are not uncommon. There have been reports of collisions with cars, as well as incidents with pets. Sea lions have also been seen dozing in playgrounds, bathing in local swimming pools, or giving birth to their young in the garden. At the same time, fences, roads and residential areas can also represent barriers for the mothers and their young on the way into the forest and thus severely limit their rearing opportunities.
Appropriate rearing areas identified
In the course of the conservation efforts, a few populations of the New Zealand sea lions have recovered and there are even the first breeding areas on the main islands of New Zealand. Her return is celebrated as a great success – but it also creates complex challenges. Because many coastal areas are densely populated on the main islands, this makes it difficult for the sea lions to reintroduce them. Veronika Frans from Michigan State University and her colleagues have therefore developed a computer model that shows potentially suitable areas along the coasts of the main islands and, unlike earlier maps, also shows where anthropogenic structures reduce suitability.
The integrated database of modeled species distributions (iSDMdb) identifies 395 potential breeding areas along the coasts of the North and South Islands of New Zealand. However, around a third of these were exposed to strong human influence in the form of housing estates or streets. “After these influences were taken into account, only around a third of the locations remained,” writes the research team. Around half of all places also had barriers in the form of pasture land or fences that would prevent the female sea lions from migrating inland. If all these human influences are taken into account, the number of suitable breeding sites drops significantly, as Frans and her colleagues report. Places on the North Island turned out to be the most undisturbed.
The scientists now hope that their mapping and the underlying database will help increase the chances of sea lions being reintroduced. Above all, rangers and authorities should use this knowledge to minimize conflicts through future environmental planning and communication with the public.
Source: Technical University of Dresden; Technical article: Methods in Ecology and Evolution, doi: 10.1111 / 2041-210X.13736