Tags

, ,

Why, one might ask, would a Canadian scientist working in the UK travel via South Africa to the most remote inhabited island in the world? The answer involves 19th-century British garrisons, fishing boats in Brazil and Namibia, Napoleon, a helicopter, and my mad Photoshop skillz.

Tristan da Cunha comprises 4 main and 2 smaller islands.  There’s the main island of Tristan da Cunha, which includes the 2060 m high Queen Mary’s Peak, and is 96 km2.  About 40 km south are two other islands: Nightingale (4 km2) with its associated Alex (or Middle) and Stoltenhoff Islands, and the aptly-named Inaccessible Island (14 km2).  Gough, the last island, is 350 km to the south, and the second largest (65 km2).  And to paraphrase the classic movie, of all the islands in all the oceans in the world, the Atlantic Yellow-nosed Albatross (Thalassarche chlororhynchos) had to nest on these four. And only these four.

And, all else being equal, the Atlantic Yellow-nosed Albatross would continue its albatrossy existence, doing what albatross do (fly, dance, breed, and repeat for 30, 40, 60, or even 70 years).  But all else is not equal.

The first problem, if you are an Atlantic Yellow-nosed Albatross, is that you are large and delicious.  Tristan had no indigenous population, and the community here today traces its origins back to only 1817 when William Glass and his family remained behind when the British garrison stationed to (somehow) prevent the liberation of Napoleon from “nearby” St. Helena (which is actually more than 2000 km away, but the closest habitation to Tristan).  On islands that were in all respects wild and rugged, the Tristanians had to adapt to the local conditions for survival, and that included harvesting the seals and seabirds that used the island.  Atlantic Yellow-nosed Albatross were a delicacy, and the eggs (measuring XX x XX mm), as well as chicks laden with fat (weighing > 2 kg each) were harvested right up through the 1950s.

In the 1950s, up to 2500 eggs were taken each year on Nightingale, with a further 1700-2000 chicks harvested later in the season (a collecting permit, incidentally, cost 1 shilling).  In fact, most of the seabirds on Tristan were exploited in some way or another.  Atlantic Yellow-nosed Albatross are now protected under the Conservation Ordinance of 2006, and what limited poaching used to exist has all but fizzled out.

The second problem, if you were an Atlantic Yellow-nosed Albatross, is that somewhere along the line, black rats were introduced to Tristan.  The current best guess is that they arrived on a shipwreck in 1882.  Rats love to eat, and when they produce 3-5 litters of 5-8 pups/litter it doesn’t take long to go through a fair number of birds. Petrels, close relatives to albatross that usually nest in burrows in the ground, are generally harder hit than albatross, which nest on the surface on pedestal nests, but the rats undoubtedly took their toll.

The third problem, if you were an Atlantic Yellow-nosed Albatross, is that longline fisheries, particularly those in Brazil and Namibian waters, tend to catch a lot of Atlantic Yellow-nosed Albatross.  In Brazil, 0.011 birds are caught for every 1000 hooks set (and when there are hundreds of thousands or millions of hooks set, you can see the numbers add up quickly).  They’re also the most common bycatch species in pelagic longlining and trawl operations in Namibia.

So in the face of these former (in the case of harvesting) and current (rats, bycatch) threats, the natural question is “Well, how many are there, and is that changing?”.  As I write this in early September 2014, I can let you in on some inside knowledge: we honestly haven’t a clue.

In the early 1970s, a chap named Richardson was on Tristan and its other islands, and came up with what were then the best estimates of the population of most of the breeding seabirds, including the Atlantic Yellow-nosed Albatross.  Since then, there was some work done on Gough about 10 years ago, a count on Nightingale in 2007, and a guess at the population breeding on Inaccessible in the early 1980s.  But the main island of Tristan remained uncounted since 1974.  Back then, the estimate was 16,000-30,000 pairs, making it the largest breeding colony for the species.

There are about 5300 pairs at Gough, 4000 at Nightingale (with another couple hundred pairs on Alex and Stoltenhoff), and 1100 pairs on Inaccessible.  Even together, they don’t eclipse the estimate from Tristan.  But that estimate is horribly out of date, and a lot has changed since 1974[citation needed].

Which brings me to the purpose of my visit: figuring out just how may Atlantic Yellow-nosed Albatrosses there are.  Now, this is much easier said than done, but thanks to our project partners at the Tristan Conservation Department and with the logistical support of the South African National Antarctic Program and Department of Environmental Affairs with the helicopters of the research ship S.A. Agulhas II, a couple hundred photos, a pile of computer memory, and the aforementioned Photoshop “mad skillz” we’ll photograph the entire island in about 3 hours from 100-200m above ground.  You can actually see albatrosses on their nests since their white backs stand out against the brown, green, and otherwise dark ground.  Stitch ‘em together and what have you got? Bippity boppity boo A massive image file where we can count the nest.

But it’s not that “easy”.  The photos will undoubtedly miss some nests, so will be supplemented with a healthy dose of groundtruthing where we hike up, count the nests in a set area, and compare this to the photo count to come up with a correction factor based on nesting habitat and other features that impede detecting the nests from the helicopter.

So what, some might be asking.  Without a good idea of how many there are, we don’t know the toll that bycatch is playing on populations.  Taking the same number of birds a year has different consequences for a species with 10,000 breeding pairs than for one with 100,000 pairs.  In fact, the lack of a current population estimate was identified by the Agreement on the Conservation of Albatrosses and Petrels, an international agreement between several nations (including the UK, and therefore Tristan da Cunha, as well as Brazil) aimed at reducing seabird bycatch (www.acap.aq), as a significant gap.  So much of a gap that they actually provided some of our funding for the current expedition.

So that, in a nutshell, is why I’m here.  Along the way, I’ll also be working with the Conservation Department looking at their current albatross monitoring program, we’ll count some penguins, trap a bunch of rats to look at their diet and distribution, and continue the work to better understand the poorly-known burrowing petrels of Tristan.

But next week, I’ll be off to Gough on the SA Agulhas II to get to know the island, hopefully do a similar Atlantic Yellow-nosed Albatross count there, and contribute to the science underpinning the hopeful eradication of introduced house mice from the island.  I won’t be back on Tristan until early October, and will likely have the next instalment of Tristan Adventure then.

Advertisements