The Sea Lion and the SLED

You may remember a post that I wrote a few months ago about the New Zealand sea lion. It was about how the largest population of this New Zealand endemic is declining rapidly on their Sub-Antarctic refuge in the Auckland Islands. While writing my e-book about Campbell Island I thought I would head across the road to interview Dr. Bruce Robertson from the University of Otago’s zoology department.

Dr. Robertson has written a number of papers about the New Zealand sea lions; their decline, population structure, genetics, and the bycatch management system. I spoke to him about the use of Sea Lion Exclusion Devices (also known as SLEDs), specifically whether or not they are effective. I was interested to hear about how the government (the Ministry for Primary Industries) have gone about testing these devices to ensure that they are working and successfully protecting this vulnerable species.

Here is his answer:


The Mystery of the Missing Sea Lions

The plight of the New Zealand Sea Lion (also known as the hooker’s sea-lion, or whakahao) appears to be a never-ending fight for survival.  Their value in the 19th century to hunters for their skins and oil meant they were hunted to near extinction until sealing was banned in the middle of the 20th century.

Today, an estimated 71% of the population take refuge in the Auckland Islands. But even 400 kilometres from the nearest city, they are still threatened with extinction. Their numbers have been dwindling for the past 10 years and in the last 3 years scientists have observed a drop in the number of pups being born on the islands.

What is the reason for these declines in both numbers and fertility? Let’s take a quick look at a few sides of a controversial and diverse debate…

1 hour old New Zealand Sea Lion pup on Enderby Island (Photo: Kimberley Collins)

The Squid Fishery – Management of Sea-Lion By-catch:

The marine life of the Auckland Islands is supposedly well protected from human influence. In 1993, an area of 12 nautical miles surrounding the islands was declared a marine mammal sanctuary. In 2003, it was upgraded to a marine reserve status. Neighbouring this marine reserve, is a well frequented squid fishery, known as SQU6T. In theory, the marine reserve should protect the wildlife from being caught and killed in trawlers, but unfortunately this is not the case for the New Zealand Sea Lion.

Location of the SQU6T fishery zones surrounding the Auckland Islands (Photo: Ministry of Fisheries)

The New Zealand sea-lion love squid and will travel vast distances to get their flippers on these tasty morsels, often well outside the 12 nautical miles of the marine reserve surrounding the islands. For fishing vessels, this means that sea lions are often caught in trawling nets while foraging and for a while dead sea-lions would frequently come to the surface in a trawling net. In response, government agencies proposed a quota to control the by-catch of sea-lions, or put simply – a control on the number of sea-lion deaths caused by trawling nets.

Over the last 10 – 15 years, however, sea-lion exclusion devices (SLEDs) were developed. Their basic function is to act as an escape route for the wayward, hungry sea-lion. They have been compulsory for all vessels trawling in the area since 2007, and when comparing the number of sea-lion deaths from 2001 (6.8 per 100 trawls) and 2011 (0 deaths per 100 trawls) we can assume that they are effective.

UPDATE (12/4/12): It has been brought to my attention that the animal in the above video has been identified as a fur seal, not a NZ sea lion!

Following the apparent success of these devices, the government is proposing that there is no longer a need for by-catch management, or the quota aforementioned. A number of environmental agencies disagree with this, and want to see further research on the effect of SLEDs on sea-lion health, an increase in the size of the existing marine mammal sanctuary, and a major reduction in the by-catch quota to zero for all fisheries.

While we know that SLED devices prevent direct mortality as a result of drowning in trawling nets, their long-term effects are not well understood.

The SLEDs are basically a gate in the trawl net that prevents a sea-lion from entering, allowing them to swim out the top through a hole in the net. While sea-lions are great at accelerating, their brakes are not as well developed and when combined with darkness and the weight of water potentially making the hole open and close irregularly, it could be a recipe for disaster. For all we know, sea-lions may be seriously injured on their escape from the SLED (head injuries are the biggest worry) and so many are also calling for research on the ‘post-escape’ health of sea lions.

The Squid Fishery – Food Depletion:

Researchers working on Enderby Island have spent time bravely attaching tracking devices to female sea-lions in an attempt to understand their feeding patterns. They have discovered that females are travelling much further to access food, which can have serious effects on the health of their young.

If a female has to travel farther than usual to access food, she will use more energy and be unable to replace it with the small amount of food she is able to find. The more energy a female is using, the less milk she can produce, and so the chances of her pup’s survival is lowered.

A 1 hour old New Zealand sea lion pup on Enderby Island has its first feed. (Photo: Kimberley Collins)


It has been suggested that The Auckland Islands are the farthest point of the New Zealand sea lion’s possible distribution and that they would do better on the mainland of New Zealand, if they were not threatened regularly by humans. This is based on comparisons made between populations on the mainland of New Zealand (specifically on the Otago Peninsula) and those on Enderby Island. Mainland populations appear to be larger and healthier, whereas the Enderby Island population appears to have stunted growth and less success in reproduction – possibly because of the difficult environment. Then again, this could be a result of the aforementioned threats from squid fisheries.


The largest colony of New Zealand sea-lions (71% of the total population) are found on Enderby Island, a small island northeast of the main Auckland Island. Researchers have watched the breeding population in Sandy Bay for a number of years, and have witnessed a number of bacterial epidemics wipe out large proportions of the population. The most signficant of these events was in 1998 when 20% of the population and 50% of all pups born died. Such events have severe repercussions on future generations and current declines in pup numbers may be the knock-on effect of these virulent, bacterial infections.

More Information:

Sailing the Sub-Antarctics

Once upon a time I somehow convinced the good people at Heritage Expeditions to let me travel on their ship, the Spirit of Enderby. We were bound for the Sub-Antarctic Islands, a region so wild that only the bravest of souls have endured the arduous journey to their shores.

I could have done the typical “kiwi O.E.” and gone to the homeland to yell at the Queen from the street outside Buckingham Palace, or joined the London haka on Waitangi Day. But no, I chose to spend 26 days island hopping in the Southern Ocean, one of the most wild and isolated environments in the world.

There’s something a little more satisfying about doing a one-person haka for a colony of 60,000 penguins. I can’t say exactly what it is, but the look of appreciation on their little black and white faces is like no other I have seen in my life. They’re great listeners, penguins. And they don’t mind my socially awkward remarks or the fact that I will tell my life story to anything with a face (inanimate objects included).

My audience of 60,000 Royal Penguins on Macquarie Island. (Photo: Kimberley Collins)

The hardest crowd to please is definitely the pinnipeds. While the fur seals are fairly relaxed and much like the stoners of the seal world, the New Zealand sea lions I met were a whole other kettle of fish. They’re like grumpy old men. Make a noise louder than a whisper and they’ll bang on the wall and should flibber-jabber remarks that only someone who was born in the 1800’s could understand. And by that I mean they will challenge you.

When a New Zealand sea lion challenges you, you’re not supposed to run. The idea is to appear bigger than him. A stick can come in handy, and I was told by a researcher on Campbell Island to stand still, be tall, and hold a stick high above my head. If that doesn’t work, the general idea is to kick the sea lion in the face and run away, although I don’t think many have resorted to that method just yet. Most scientists would rather get bitten than live with the knowledge that they kicked an endangered species in the face.

The hunk of burning love that challenged me on Enderby Island. (Photo: Kimberley Collins)

So you can see why I am slightly neurotic about the region. There are stories to be told and adventures to be had and that’s why I have chosen to blog about the Sub-Antarctic Islands. Not to convince you that they are a valuable and irreplaceable ecosystem that deserve every New Zealanders undying attention (you should have received that memo at birth), but to tell you the stories that make the Sub-Antarctic stand out from the crowd and unlike any environment in the world. Bear with me, there are only so many adjectives that one can use to describe this region.