Above picture: The Prince Edward Island 2023 Expedition members smile for the camera, with the S.A. Agulhas II offshore; photograph by David Hedding

South Africa’s sub-Antarctic Prince Edward Islands, consisting of Marion Island and Prince Edward Island (PEI), were declared a Special Nature Reserve in 1995.  Together, they form an internationally important breeding site for a diversity of seals and seabirds.  Most of these species breed during the summer months, when invertebrate and plant activity and growth are also at their highest.  Invasive House Mice have caused detrimental effects on several sub-Antarctic islands.  On Marion and Gough Islands, predation by mice threatens the viability of seabird species, and disrupts nutrient cycling by native insects and plants.  These effects become magnified when we observe similar islands without their presence, such as PEI, where the biota is thriving.

The two stratified tuff promontories of Golden Gate make for a striking feature; photograph by David Hedding

On 14 November 2023, a party of 13 visited PEI by helicopter for a long overdue, and highly anticipated, scientific expedition.  Unlike its nearby neighbour, Marion Island, where South Africa has a permanent research station served by annual relief visits, PEI has no permanent human presence, and even short-duration visits to the island are few and far between.  The current Management Plan for the Prince Edward Islands Special Nature Reserve permits visits of up to eight days, at intervals of five years or longer, by a restricted number of researchers.  In recent years, interdisciplinary summer surveys were conducted in December 2001 and again in December 2008.  Exceptions were made for short visits in April 2010 and March 2011, conducting biological surveys (click here) and making archaeological observations.  Since then there has been a gap of over a decade with no landings made.

Access to PEI is strictly controlled because it is one of the most pristine islands globally.  Importantly, it has always been free of alien mammals, and House Mice in particular, and thus has been spared the ecological impacts that mice have had on other sub-Antarctic islands, such as Marion.  Visits to such islands always pose a risk of new introductions of invasive species, so strict biosecurity guidelines for PEI specify that all equipment and field clothing must be brand new or subject to stringent biosecurity inspections pre-embarkation and onboard the vessel to prevent the introduction of new alien species.

The 1948 flagpole and copper plaque at the entrance to Annexation Cave behind Cave Bay, Prince Edward Island; photograph by David Hedding

The 2023 PEI survey team was one of the most diverse scientific groups to have visited the island.  The team included four ornithologists, three marine mammalogists, a botanist, entomologist, aeronautical engineer, geomorphologist, veterinarian and an environmental compliance officer.  Apart from the 75-year-old annexation flagpole and copper plaque, which still stand guard at the entrance to Annexation Cave in Cave Bay, there are no signs of past human presence on the island, save for a few remnants of the sealing age in the first half of the 19th century. However, there are many washed-up plastic fishing buoys and bottles around South Cape and in McNish Bay, spoiling an otherwise pristine scene.  A tented camp was pitched in a predetermined area near Cave Bay, next to a stream that allowed drinking water to be collected.  Camping proved somewhat challenging as the infamous Roaring Forties lived up to their name, collapsing the team’s food storage and cooking tent on the first night.  Although also taking a beating through the team’s week-long stay at PEI, the smaller sleeping tents fared better and provided welcome shelter and refuge for the remainder of the expedition.

The tented camp site above Cave Bay on a good-weather day; photograph by Elsa van Ginkel

Most of the work was performed in the south-east corner of the island, within a day’s walk of the camp.  This section of the island hosts almost all the beaches, breeding colonies and vegetation types required by the scientists to fulfil their set outcomes.  Due to steep cliffs it is not possible to walk round the island’s entire coastline.  However, a small contingent of the team braved the harsh, mist-covered interior and a steep and slippery descent (~500 m) down the escarpment to cross over to the north-western side of the island.  Here they set up a satellite camp for a couple of nights to complete surveys.  Two of the team, Charlene Janion-Scheepers and Elsa van Ginkel (a previous MFM overwintering researcher on Marion), summited the island, climbing Van Zinderen Bakker Peak at 672 m, surely among the very few women who have done so.

Wandering Albatrosses approach fledging in Albatross Valley, Prince Edward Island; photograph by Chris Oosthuizen

The waterfall at the head of Prince Edward Island’s Albatross Valley is surrounded by ledges supporting hundreds of breeding Grey-headed and Indian Yellow-nosed Albatrosses. The latter species does not breed on Marion; photograph by David Hedding

Southern Elephant Seals and King Penguins cluster on the black volcanic sand of Boggel Beach on Prince Edward Island’s east coast; photograph by David Hedding

All the surface-breeding birds, including four species of penguins, five species of albatrosses (of which only four breed on Marion), Northern and Southern Giant Petrels and Subantarctic or Brown Skuas, were surveyed and counted or estimated.  An unexpected sighting was of an unbanded Black-browed Albatross close to an empty nest, the first record for the island, and one of only three known for the island group (click here).  In addition, transects conducted in the late 1970s were repeated to estimate the density and occurrence of burrowing petrels.  Most of the recently born Southern Elephant Seal pups were marked with flipper tags to estimate movements of individuals between PEI and Marion Island.  A variety of birds and seals was examined for potential pathogens and/or toxins.

Poa cookii tussock inflorescences were abundant in the absence of mice on Prince Edward Island; photograph by Elsa van Ginkel

Flightless moth caterpillars were easily spotted on Prince Edward. On Marion they fall victim to mice and are very hard to find; photograph by Elsa van Ginkel

Vegetation surveys were completed in coastal salt-spray, biotic herbfield, mire, slope and fellfield habitats, accompanied by invertebrate and soil nutrient collections to compare with concurrent data from Marion Island.  Adults and larvae of the endemic flightless moth Pringleophaga marioni were abundant in all habitats in comparison with Marion where they are preyed upon by mice, while the spiders were surprisingly large in comparison to those to be seen on Marion Island.  Even tiny invertebrates such as springtails were clearly different along the coastline compared to Marion.  Two temporary wind stations were erected to measure wind speed and direction and major geological features and buried peat depositions were sampled.

Marion Island’s snow-covered peaks are visible 22 km away from behind Hoedberg on the Prince Edward Island plateau, photograph by Janine Schoombie


All the scientists on the team have worked extensively on Marion Island, and comparisons between the two islands were unavoidable.   Even while setting up camp, it was immediately apparent that PEI is very different from Marion Island.  Within minutes of our arrival an adult flightless moth crawled onto our gear.  In addition, expansive areas of numerous tightly packed petrel burrows had to be traversed, in great contrast to Marion.


Our observations from our visit to a sub-Antarctic gem are summarised in the following statements, with most alluding to the lack of mice:

“The island is very dry, there were a lot of mud flats that looked like dried up marsh pans.”

“The numbers of debris flows and small landslides were surprising”.

Azorella cushion plants are everywhere, with extensive flats completely covered by them.”

“The invertebrate life is in complete contrast to Marion, with ‘goggas’ crawling everywhere you look.  Even the occasional uninvited spider entered our tents.”

“There are burrows everywhere! The abundance of burrowing birds was strikingly notable.”

“The scavengers seemed less desperate, with half-eaten petrel carcasses often observed lying next to skua nests.”

“The Gentoo Penguins parade with curiosity, often approaching and following us when nearing their colonies.”


We learnt a lot during our short stay on the island and we will learn even more as we start to analyse our data.  Comparisons between the plant, invertebrate and seabird surveys from our visit, and parallel data collected using the same methods on Marion Island, will be invaluable components of monitoring impacts of the Marion mouse eradication in years to come.  The excitement will take a while to wear off (if it ever does) and knowing that we were fortunate to visit an (almost) pristine ecosystem is something that none of us will ever forget.  Our short visit over 14 – 20 November confirmed how privileged we were, and what the Marion Island ecosystem should really be like, and could be, without House Mice.  Let’s act where we can and make Marion Island free of mice as soon as is feasible.

The survey team thanks the South African National Antarctic Programme through the Department of Forestry, Fisheries and the Environment (DFFE), the Department of Science and Innovation and the South African National Research Foundation, the officers and crew of the S.A. Agulhas II (African Marine Solutions – AMSOL) and the helicopter crew from Ultimate HELI for making the expedition possible.

Azwianewi Makhado (Chief Scientist & Ornithologist, DFFE), Maëlle Connan (Ornithologist, Nelson Mandela University), David Hedding (Geomorphologist, University of South Africa), Charlene Janion-Scheepers (Entomologist, University of Cape Town), Rowan Jordaan (Marine mammal scientist, University of Pretoria), Makhudu Masotla (Ornithologist, DFFE), Thomas Mufanadzo (Environmental Control Officer, DFFE), Chris Oosthuizen (Marine mammal scientist, University of Cape Town), Liezl Pretorius (Veterinarian & Marine mammal scientist, University of Pretoria), Janine Schoombie (Aeronautical engineer, University of Pretoria), Stefan Schoombie (Ornithologist, University of Cape Town), Yinhla Shihlomule (Marine mammal scientist, University of Pretoria), and Elsa van Ginkel (Botanist, University of Pretoria), 19 December 2023.