Popping the seal: The fall and rise of the New Zealand fur seal population

The Nuggets are a magical place. (Image from Adrian Paterson)

One of my favorite places is the Catlins, a wild area of dripping bush, rugged southerlies, untouched beaches, and abundant wildlife in the far south-east South Island. There are some great spots within the Catlins, but the one I go back to time after time is The Nuggets. This area is a peninsula at the north end of the Catlins, that gives some protection to the swimming beaches of Kaka Point from weather and waves that roll in straight from the Antarctic, ends in high cliffs and a knife back ridge upon which sits a working lighthouse. Sprinkled off the end of the ridge are the rock stacks that make up The Nuggets.

The views are stupendous. The wildlife is not far behind. Yellow-eyed Penguins make their home in the coastal scrub along the peninsula and you can watch them waddle ashore in Roaring Bay. Gulls and terns flit and glide among the waves. And there are seals, hundreds of seals.

I grew up in South Otago, about 25 minutes away. When I was a child (in the 70s) we would often take guests down to The Nuggets to see the views but also to view the seals. At that time you could use a long and thick rope to help you walk down to the colony at the base of the lighthouse ridge and walk into the fur seal colony. This was very cool. At that time there were not a lot of seals around  New Zealand. Most people had not seen them in the wild, let alone up close. At the Nuggets there were 20-40 of them in a colony. It was a thrill to see (and smell and hear) the seals, to watch them frolicking in the kelp beds. Forty years later, things have changed.

When I ask my first year classes if they have been up close to a fur seal almost 100% of them have had this experience. Fur seals are now found on many coast lines around the South Island and lower North Island and they are found in large numbers. It seems that the species is growing and expanding in numbers and has increased at a phenomenal rate. Recently, while boogie-boarding at Kaka Point a seal decided to surf in beside me all the way to the beach. This never happened to me as a child. And I spent a lot of time in the sea as a kid.

Fur seals (Image from Adrian Paterson)

As fur seal numbers increase they are setting up new colonies in new areas, and moving into new regions where they have seldom been seen. On one hand this is great, here is a New Zealand native species that is doing well. On the other hand this is creating a few issues, here is a species that might just form a large and smelly colony in front of your million dollar beach house. Or eat a lot of the fish that you might want to go and catch yourself. Managing fur seals is going to become a much larger job in the future.

One question that I have wanted to answer is just how big could the fur seal population get? One way to answer this would be to work out how large the population was before humans arrived in New Zealand 7-800 years ago. This pre-human population would give us an estimate the best (or worst) case scenario for seal population growth. It would allow us to put the current population in perspective, is it near the limit or can it grow a lot more? Work with my PhD student Arsalan Khoyi-Emami and colleagues from Lincoln University and the Department of Conservation has allowed us to shine some light on this question.

In a paper published in Mitochondrial DNA we tell how we obtained samples from 186 fur seals from around New Zealand and also the Bounty Islands in the Subantarctic. We got information from whole mitochondrial genomes for each of these seals which allowed us to look at how genetically different the various colonies and areas were from each other. Through the wonders of DNA models and Bayesian statistics we were also able to estimate the size of the fur seal populations at the lowest point (the ‘bottleneck’ caused by European sealing), the impact of Maori (the population size just before Europeans arrived) and the pre-human population.

An increasingly common sight, NZ fur seal sleeping on a beach near you. (Image by Adrian Paterson)

Normally, when populations pass through a bottleneck, genetic variation is lost (through drift). With the fur seals we found a large diversity still remained. However, the genetic differences were actually very similar to one another. Imagine you have a swimming pool which springs a leak. Usually this will only leave a few puddles at the bottom. The fur seals are more like they have retained water up to your ankles, useful for paddling about in, better than a puddle, but not the same as if you were able to swim.

Population numbers today are estimated by DoC at around 200,000 fur seals. Our analyses suggest that pre-human numbers were around 2.5-3 million. Maori caused some impact on numbers as there were 1.5-1.8 million fur seals when Europeans arrived. Within 50 years European sealing had reduced the population to about 10,000 (or less than 0.5% of the original population).

The fur seal population of today is between 5 and 10% of what it was before humans arrived. It is very likely that the fur seal population can, and will, continue to grow considerably from what we see today. Our previous work showed that fur seals are likely expanding their range by colonizing at the fringe of their range (rather than from overspill from central colonies) and that fur seals are generalist feeders who diet does include commercially important species. So our future will see more seals, new colonies in areas settled by humans, and some competition for fish species of interest to humans. In short, lots of wildlife management issues to solve so that humans and seals can continue to live together.

Next time I visit the Catlins, I will expect to see more seals and in more places.  Surfing with them may become a commonplace event.

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