In their new book, writer Laurence Fearnley and photographer Arno Gasteiger follow the 45th parallel south, a circle of latitude which theoretically marks the midway point between the equator and the South Pole.
I am fortunate enough to have been born in Canterbury, raised in Christchurch and now to live in Dunedin. I cross latitude 45 South several times a year, en route to Christchurch to visit my mother. In truth I don't pay as much attention to this invisible line as I do to the crossing of the braided Waitaki River, a few kilometres north of Hilderthorpe.
Really, for me, the 45th parallel is a kind of geographical equivalent to a favourite volume of poetry. It is not something I feel compelled to explore from start to finish - from east to west - but, rather, something I am happy to dip into and which lets me experience a sense of wonder and gratitude as I stumble along.
In some ways 45 South forms the background theme to many of the activities I have pursued over the past 40 years - physical activities such as kayaking or walking, as well as creative personal pursuits such as writing.
When I started thinking about a text to accompany Arno Gasteiger's photographs and opened my New Zealand atlas to identify the places along the 45th parallel I was surprised by how often I had, in fact, touched on it.
In my time as a keen kayaker, I have navigated down various rivers - the Manuherikia, the Clutha, the Kawarau, the Shotover, Mararoa and Eglinton - all of which brush 45 South at some point on their journey.
As someone who likes camping and walking (though I don't feel I quite fulfil the requirements of a proper South Island tramper) I have also pitched my tent along the 45th, enjoying landscapes as varied as tussock highlands, beech forests and river valleys. In both cases - kayaking and camping - I have felt privileged to spend time in such beautiful surroundings and mindful that, as wilderness areas, these places are threatened.
Visiting the region of the 45th has also made me think about who I am as a first-generation New Zealander. Sections of my novels - and in particular Butler's Ringlet and Edwin and Matilda - have been set in locations dotted along latitude 45.
I refer to the Department of Conservation 45th Parallel signpost in Butler's Ringlet, by way of protesting against what I consider an excessive amount of signage along South Island scenic roads.
But what I really think about when I travel or write about the landscape of 45 South is how much I love the land, how much joy it brings me, and how precious it is.
It's hard to guess what the future of Otago and Fiordland will be - whether the last glimmer of frontier and wilderness will eventually fade. It seems odd, in a way, that even if this part of the South Island were to become unrecognisable, there would always be one unchangeable feature, a feature you can't even see: latitude 45 South.
Afloat on the Eglinton
Rivers seem to have moods, if not personalities - at least that's how it feels to me when I kayak them. And for me, the Eglinton River is a "happy" river. Technically it is very easy: there are no rapids to speak of and the only rough water results from shoals descending into calm pools.
At one point, the river enters a short gorge, a slow-moving stretch of deep water that emerges into river flats below, near Te Anau Downs. But to write of the Eglinton in terms of its technical difficulty is to miss the point: the Eglinton is the kind of river that makes you glad to be alive - it is that beautiful.
The put-in spot for our journey is near a stretch of road that was once marked on tourist maps as "The Avenue of the Disappearing Mountain".
This avenue is one of the few straight sections of the Milford Highway and was noteworthy for the way "the mountain" at the end of the straight would slowly disappear, as if being swallowed into the ground.
Watching the mountain vanish used to be one of the highlights of the journey to Milford when I was a kid, but now the trees either side of the road are so high that this phenomenon no longer occurs - and so the road sign marking this "wonder" has also disappeared.
However, the yellow-on-green Department of Conservation sign marking the 45th parallel - the final such sign on this cross- country journey- is still there beside the road, nestled among moss- and lichen-covered beech trees, and the subject of thousands of photographs taken by tourists passing by on their way to Milford Sound.
The river, of course, flows away from the mountains. Usually this is one of the disadvantages of kayaking: that you tend to be facing away from the scenery, travelling from somewhere very beautiful to a place less picturesque.
But this isn't a problem with the Eglinton because the river itself is so perfect, the water so clear.
As you near each small rapid, the air itself seems to become fresher, a cool breeze rises up from the surface and is soon accompanied by repeated splashes to the face with ice-cold water.
As you go through the rapid, the splashes become firmer, more like slaps, and the prow of the kayak digs into each wave with a pleasing feeling of resistance. Most rapids usually end with bouncy rolling waves that make you laugh, and then you reach an eddy where you can swing around to face the section of rapid you have just kayaked.
It is while you are resting here at the side of the river, waiting for your friends to come through, that you tend to drop your hands into the water, filtering the sediment through your fingers in an absent-minded search for lumps of gold.
Prior to the spread of didymo - a diatom that is green- grey in colour and looks like sodden toilet paper or, when dry, like the contents of a vacuum cleaner bag - the stones along the river edge shone or glistened, due to the presence of mica.
As recently as the 1920s there may have been signs of other glistening objects: not gold or mica but graylings (Prototroctes oxyrhynchus), New Zealand's only extinct freshwater fish.
Not far from the Eglinton is the Upukerora River, which runs into Lake Te Anau near the present-day township.
This river carries the Maori name - more correctly spelt Upokororo - for the New Zealand grayling, a spelt-like fish that was once found in large shoals throughout New Zealand's lowland rivers and streams.
Like whitebait, the grayling hatched and spawned in fresh water and was then washed out to sea where it remained until maturity, before travelling upriver once more.
There are very few specimens of this fish in existence - the last recorded specimen was delivered to the British Museum in the 1930s - but it grew to around 12 to 18 inches (300 to 450mm), had scales and an adipose fin (the small, fleshy fin located between the dorsal fin and the tail).
The grayling was very common up until the 1860s - so common that it was caught in nets, but also as a "sport" fish with rod and fly. Its decline began in the 1870s and by 1923 it had disappeared.
Why it disappeared is a bit of a mystery. One reason might be that it could not compete with trout, which were introduced to this country from the 1860s.
Or it could be that deforestation of watersheds and river banks caused changes in river flows, more floods and droughts, or increased exposure to sunlight which raised the temperature of the water.
But neither of these claims can be made with absolute certainty. What does appear to be certain is that the grayling had an unusual odour, like cucumber.
I have seen trout in the Eglinton River. At the point where the river enters the short gorge, it is possible to drift downstream and gaze down through the water to see, 20 or 30 feet below, large fish sitting on the riverbed. It's always a thrill to see a big fish in a river.
The Buller has eels as thick as my leg, but these southern rivers - the Eglinton, the Mararoa, the Shotover and Matukituki - carry trout and it is such a privilege to watch them, undisturbed by the kayak's shadow or the presence of fishermen.
Towards evening we make camp at Deer Flat, debating whether it is preferable to erect the tents under the shelter of the beech trees or out on the flat where there will be frost but also sun in the morning.
Once the last tourist bus has left the area the road becomes quiet and the forest, too, is still.
There are bats in this valley - both long-tailed and short-tailed - but, although they might be roosting nearby, I have never seen them.
Nor have I ever seen a mohua, or yellowhead - which, like the bats, is being carefully monitored by the Department of Conservation.
There is one small bird that is always present: a South Island robin. It comes close to the tent, poking around in the fallen beech leaves on the forest floor.
At times it perches on the tent itself and, if you are inside, you can see its long claws silhouetted against the flysheet as it hops along the tight fabric of the tent.
As the sun descends it becomes eerily quiet, the only noise the sound of the river and the occasional muffled call of a paradise duck somewhere out on the river flats.
It's dark by 7.30pm and the sun will not reach this spot of the valley until well after nine.
The ground beneath our sleeping bags is hard but our bodies still retain the soft, swelling motion of the water, the rise and fall of the waves, which is soon echoed in sleep.
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