Dr Philipp Boersch‑Supan

Marine & Quantitative Ecologist

Campbell Island - A life boat in a changing ocean

Many populations of sub-antarctic animals and plants are in decline, threatened by an array of direct and indirect human impacts. The restoration and protection of predator-free island habitats is a crucial component of conservation measures to ensure population persistence in a changing world.

In late 2016 I was awarded an Enderby Trust scholarship to visit the sub-antarctic islands of New Zealand. Here are my impressions from Campbell Island.

A bare patch of volcanic rock marks the final climb to the ridge line, then the path disappears in waist high tussock. A startled Campbell Snipe jumps into the air and dashes downhill in erratic zig-zags. We pause for a moment just below the ridge crest, to take shelter from the winds and the drizzle they carry. Strong winds circle the globe at this latitude. Largely unbroken by land they sweep the ocean separating Antarctica from the rest of the world and make the Southern Ocean home to the majority of albatross species. But on this grey morning, there is little activity in the colony on the hill- side. Only when we step onto the ridge crest, white spots become apparent in the tussocks on the hill side. Southern Royal Albatross, huddling on their nests. Some have their beaks tucked under their wings, others sit quietly, inspecting our small group.

A Southern Royal Albatross Diomedea epomorpha on Campbell Island.

It is early in the breeding season and the birds have just begun to lay the single egg that each will be incubating this year. Royal Albatrosses usually only breed every other year, but those that are breeding this year have occupied their nest sites and are guarding them, while their partners are out at sea feeding.

We cross the ridge, leaning into the wind before descending the windward hillside. Tussocks and ferns give way to a meadow of megaherbs. Colourful stands of yellow, purple, and greenish-white flowers. In the midst of it sits a pair of Sub-antarctic Skua. Further down, on the cliffs edge, nestled in between purple flowering stands of Anisotome latifolia. sit the chicks of Giant Petrels. Already the size of a Christmas turkey they are starting to loose their down and are growing their first set of feathers. Beyond them jagged limestone cliffs drop into the sea. A pair of Light-mantled albatross dash along the coast line and out onto the sea. The sooty coloured birds with paler backs and bright white rings around their eyes are performing an airborne courtship dance, each taking turns at leading a synchronised display of flight skills.

Northern Giant Petrel chick Macronectes halli.

Courtship display of two Light-mantled albatross Phoebetria palpebrata.

Tussocks dominate again, then a thick brush formed by grass trees, ferns, and Myrsine divaricata as the path disappears into a steep gully down towards the beach. The track is well trodden - it is a route used by the locals: shy hoiho or Yellow-eyed Penguins commute along it from their marine foraging grounds to their nests which are hidden in the scrub. New Zealand fur seals also wander along here on occasion, usually subadults on the search for unpartnered females.

The cut opens as we reach the shore. A small bay with a pebbly beach covered in strands of bull kelp. Above the tide line a massive hunk of blubber. A Southern Elephant Seal bull, hauled out here to moult. Behind him a handful of smaller conspecifics, most of them juveniles, recently weaned from their mothers.

Our hike across the island has revealed rich plant and animal communities, and it would not be far fetched to think that this wild island is a pristine outcrop in the Southern Ocean. Yet, over the past 200 years humans have left their mark: Sealers almost completely eradicated the local fur seal population in just a few years after Campbell Island was discovered in 1810. Whaling followed, then the establishment of a pastoral lease. Human activities introduced not only cattle and sheep on the island, but with them also predatory mammals such as rats and cats. The consequences were disastrous: Rats and cats were literally eating the local birds, extinguishing the unique Campbell Island Teal and Snipe on the main island.

Rats - together with feral live stock - also decimated the unique plant life on the island. Even after the sealing and whaling had ceased, the pastoral lease had been given up, and Campbell was declared a nature reserve in 1954, the introduced mammals continued to wreak havoc on the island’s ecosystem. The deadly combination of human exploitation and introduced predators was not just a problem for Campbell. Most sub-antarctic islands have been altered by the same or similar human impacts.

A Campbell Island Snipe Coenocorypha aucklandica perseverance in a Bulbinella stand.

Luckily for Campbell, all was not lost. As the result of decades of conservation work the island is slowly regenerating. Sheep were successively excluded from the island starting in the 1970s, and completely removed in 1991. Cattle were removed in 1987, and the cats died out for unknown reasons sometime before the 1990s. The rats persisted, however, and it was not until 2001 that they, too, were eradicated. The rat eradication, undertaken by spreading poisonous cereal baits from helicopters, was the largest ever attempted at its completion, and set an enormously successful example to more recent and ongoing eradication programs around the globe.

Since the eradication, the plants and animals on Campbell are regenerating. Seabirds returned, the Campbell Island Snipe and Pipit recolonized the island from remnant populations on rat-free outlying islets, and in a serendipitous twist, the Campbell Island Teal - thought to have been driven to extinction by cats and rats - was rediscovered in 1975 on Dent Island, an islet in Campbell’s Cattle Bay. Captive breeding ensured the survival of this species, until it could be successfully reintroduced to its home following the rat eradication.

The plants are regenerating as well. Megaherbs now form colourful fields on the hillsides, providing Spring time visitors with a re- markable scenery, while strict regulations ensure that human visitors do not harass the wild life or bring new unwelcome plants or animals to this sub-antarctic jewel.

All well that ends well? one could ask at this point. Sadly, further conservation and protection measures are necessary. Restoring and protecting island habitats is necessary to safeguard sub-antarctic species, but not sufficient for all of them. Seabirds and seals do not live on islands alone, they are true ocean wanderers, covering vast distances in the polar oceans. They are at threat from bycatch in fisheries beyond the reserve boundaries, and from pollution. And both on and off the islands, all species are feeling the impacts of a changing climate. Temperatures are rising, rainfall and wind patterns are changing, as are ocean currents and the food they carry. Scientists still have an incomplete understanding of the effects these changes will have on the animals and plants of the Southern Ocean, but it is clear that to mitigate the effects of climate change we must strive to remove as many other stressors as possible from wild populations. Restored and strictly protected islands like Campbell are life boats in a changing ocean, but to make them as effective as possible we also have to work harder to eliminate fisheries bycatch of vulnerable species, and to greatly reduce the amounts of plastic waste and chemical pollutants we release into the oceans.

It is afternoon as we make our way back to Perseverance Harbour. The clouds have parted slightly, and buoyed by a steady breeze more and more Royal Albatross return to the island. With their massive wingspan they soar over our heads as they pick out their partners on the hillside. Once reunited, pairs greet each other and engage in mutual preening. Elsewhere, groups of juveniles are busy socialising. In a behaviour known as gamming they form small circles, where they take turns in an astonishing display: One at a time, they call towards the sky, wings outstretched and head and neck stretched upward. They croak, they yap, they clasp each other’s bills and shake their heads. A magnificent and touching display at once.

A sky-calling Southern Royal Albatross.

Eventually we move on, albeit reluctantly, to descend through tussock and scrub until we reach Garden Cove. Pipits sing from the flowering Dracophyllum grass trees, and terns shriek as they hover over the shallows. As we return to the Spirit of Enderby, our cameras filled with images and our heads with memories, a lonely Sitka spruce remains back on shore. Over a hundred years old, and thousands of miles away from its species’ home range in North America, it is a poignant reminder of the long human history on Campbell, and our meddling with the island’s ecosystem.

Philipp Boersch-Supan is a postdoctoral researcher at the University of Florida. He studies the ecology of albatrosses and other animals of the open ocean. His trip to Campbell Island was made possible through the generous support of the Enderby Trust.

World Seabird Twitter Conference: Surface temperatures of albatross eggs

Once again the World Seabird Union organized a succesful Twitter event this year, the 3rd World Seabird Twitter conference.

Our contribution focussed on thermal traits of albatross eggs, which are important input data for mechanistic models for albatross growth and bioenergetics.

If you would like to join the seabirder community on twitter, have a look at #SeabirderSaturday!

New open access paper - Marine microbial communities correspond to regional oceanography

New paper published on marine microbial biogeography:

Microbe biogeography tracks water masses in a dynamic oceanic frontal system lead by Anni Djurhuus describes how microbial communities in the Southwest Indian Ocean are separated by oceanic fronts. graphical summary

New paper - Seabird recovery following predator eradications on islands

Protecting seabirds is a global conservation priority given that 29% of seabird species are threatened with extinction. One of the most acute threats to seabirds is the presence of introduced predators, which depredate seabirds at all life stages, from eggs to adults. Consequently, eradication of invasive predators has been identified as an effective and commonly used approach to seabird conservation.

New Zealand storm petrel chick
New Zealand storm petrels are among the species impacted by invasive predators. Photo: S. Borrelle

Millions of dollars are spent on removing predators from offshore islands in the aim of protecting seabirds and island biodiversity. However, post-eradication monitoring is limited, so our understanding of how and if seabirds and their island habitats recover is also limited.

Our new paper, lead by Stephanie Borrelle from the Institute for Applied Ecology New Zealand, investigated the recovery of seabirds to islands in the Hauraki Gulf, New Zealand to try and contribute to understanding these recovery processes better. We found that on islands cleared of predators seabirds recover over time, and such islands have more diverse seabird assemblages than islands that never had predators. Recovery appears to be influenced by a suite of site- and species-specific factors. Managers may assume that given enough time following eradication of predators, seabirds will recolonize an island. Although time is a factor, proximity to source populations and human activities has a significant effect on recolonization by seabirds, as do demographic traits, colonizing ability and habitat suitability.

The paper was published online in the conservation journal Oryx. A free preprint is available here.

Borrelle, S. B., Boersch-Supan, P. H., Gaskin, C. P., & Towns, D. R. (2016). Influences on recovery of seabirds on islands where invasive predators have been eradicated, with a focus on Procellariiformes. Oryx, doi:10.1017/S0030605316000880.

Mapping my trip with GMT and Inkscape

This morning I tweeted some maps of my upcoming trip to sub-antarctic New Zealand. Here is how I made them.

For most of my dealings with spatial data I use either R (with it’s great ecosystem of ), or a full-fledged GIS package such as GRASS or QGIS (if I need a more interactive work environment and/or particular geoinformatics tools). This combination covers pretty much all the bases for my spatial analysis and mapping needs. However, occasionally I want to make a pretty map that isn’t rectangular (usually world maps, or maps of large sections of the world) and/or one that is projected in a certain way. Maybe something like this figure of the circulation in the Southern Indian Ocean I made for my PhD thesis:

SWIO circulation

Making “publication quality” maps in all kinds of projections is a real strength of the Generic Mapping Tools aka GMT, a software suite that is popular with marine geologists and is firmly grounded in the unix paradigm of one tool - one command line utility. As such the syntax and the mapping workflow may seem like a blast from the past for many (cool kids use D3 for fancy maps these days, but apparently I’m not one of them) - but with a moderate amount of pain one can get beautiful maps that put your old Mercator or unprojected WGS84 rectangles to shame.

GMT natively writes all output to postscript files, which makes the resulting maps editable in vector graphics software such as Inkscape. This is great for tweaking or polishing graphics that go beyond maps of spatial data. In the above figure of ocean currents, for example, I used GMT to plot the globe and the bathymetry (subsea topography), but the stylized fronts and currents were added in Inkscape (based on projected coordinates of frontal locations plotted with GMT in an intermediate step).

I did something similar, but much simpler, for the maps I tweeted today, and I’ll show the individual steps below.

Step 1: Draw the map

I adapted one of the GMT examples to show what’s on the opposite side of the world during my trip. The code for this is given below, and also in the script antipodes.sh on github.

This time I was happy with the GMT output as is, so no post-GMT modifications.

#	  This map is a quick and dirty adaptation of GMT EXAMPLE 25
#   (using GMT 5.4.0_r17345)
# Purpose:	Display distribution of antipode types around NZ
# GMT modules:	gmtset, grdlandmask, grdmath, grd2xyz, gmtmath, grdimage, pscoast, pslegend
# Unix progs:	cat
# Create D minutes global grid with -1 over oceans and +1 over land
gmt grdlandmask -Rg -I${D}m -Dc -A500 -N-1/1/1/1/1 -r -Gwetdry.nc
# Manipulate so -1 means ocean/ocean antipode, +1 = land/land, and 0 elsewhere
gmt grdmath -fg wetdry.nc DUP 180 ROTX FLIPUD ADD 2 DIV = key.nc
# Calculate percentage area of each type of antipode match.
gmt grdmath -Rg -I${D}m -r Y COSD 60 $D DIV 360 MUL DUP MUL PI DIV DIV 100 MUL = scale.nc
gmt grdmath -fg key.nc -1 EQ 0 NAN scale.nc MUL = tmp.nc
gmt grd2xyz tmp.nc -s -ZTLf > key.b
ocean=`gmt math -bi1f -Ca -S key.b SUM UPPER RINT =`
gmt grdmath -fg key.nc 1 EQ 0 NAN scale.nc MUL = tmp.nc
gmt grd2xyz tmp.nc -s -ZTLf > key.b
land=`gmt math -bi1f -Ca -S key.b SUM UPPER RINT =`
gmt grdmath -fg key.nc 0 EQ 0 NAN scale.nc MUL = tmp.nc
gmt grd2xyz tmp.nc -s -ZTLf > key.b
mixed=`gmt math -bi1f -Ca -S key.b SUM UPPER RINT =`
# Generate corresponding color table
gmt makecpt -Cblue,gray,red -T-1.5/1.5/1 -N > key.cpt
# Create the final plot and overlay coastlines
#plot antipodes raster
gmt grdimage key.nc -R${range} -J${proj} -Ckey.cpt -B10/10 -P -K > $psfile
#overplot landcover
gmt pscoast -R${range} -J${proj} -Dl -A0/0/1 -G35 -W0.4p -O -K >> $psfile
#add legend
gmt pslegend -R${range} -J${proj} -O -DJBC+w4.5i -Y-0.75i >> $psfile << END
N 2
S 0.15i s 0.2i gray  0.25p 0.3i Terrestrial Antipodes
S 0.15i s 0.2i blue 0.25p 0.3i Oceanic Antipodes 
#convert to PNG
gmt psconvert -Tg -A $psfile
#remove intermediate results
rm -f wetdry.nc scale.nc key.nc tmp.nc key.cpt key.b gmt.conf

antipodes map