Gough and Inaccessible Islands

Unlicensed fishing and illegal use of driftnets around the reserve has been reported (Pearce, 1999), but the threat originating from these practices is now not as serious as that of long-line fishing throughout the Southern Ocean (UNEP-WCMC, 2011). Furthermore, with the expansion of the marine protection zone in the Tristan da Cunha EEZ, fishing areas have been greatly reduced and controls have been enhanced. Nevertheless, ocean wandering species that these sites are important for (e.g. Tristan Albatross) do not recognise the boundaries of MPA’s and continue to be caught as “by catch” on the South Atlantic Ocean due to inadequate mitigation measures and observer rates within off shore fleets. This pressure is growing as more fleets fish, both regulated and unregulated in the Southern Blue Fin Tuna fleet for example (IUCN Consultation, 2025), posing a high threat to seabird populations.

Mortality from accidental by-catch by long-line fishing is a major global threat for most albatross and many petrel species (Anderson et al., 2011), including for at least six of the species contributing to the values of the site (UNEP-WCMC, 2011; Wanless et al., 2009). This remains a high threat as long as available best practice mitigation devices and techniques are not enforced effectively (Anderson et al., 2011; Kroodsma et al. 2023), applied more widely and enhanced. Tracking data of seabirds revealed that they forage at seamounts in the Tristan da Cunha EEZ, the Patagonian Shelf and the waters off South Africa, which are also target areas for fisheries and therefore increase the risk of interaction (Requena et al., 2020; Dias et al., 2017; Bentley et al., 2024). As part of the licence conditions for longline fishing, several technical mitigation measures to reduce interactions during fishing operations, such as line weightings and night setting, are required while fishing within the EEZ (Tristan da Cunha Government, 2021) - however, many species forage outside of the EEZ and are exposed to poorly regulated fisheries in the high seas (Dias et al., 2017). There is some indication that survival of albatrosses at sea may have improved slightly, but longer timeseries of mark-recapture data are required to understand how much juvenile survival at sea has changed since bycatch mitigation measures were implemented in key fisheries (Oppel et al., 2022; da Rocha et al., 2021).

While the likelihood of trans-oceanic shipping collisions is not high, the associated pollution in the form of oil, fuel and cargo spillage has the potential to cause a significant impact on the site’s marine environment. The remoteness and meteorological conditions pose significant challenges to any response to any incidents and possible resulting pollution. The economic reliance of the local community on the fisheries and high environmental sensitivity means this is a high-risk region for hazards from international shipping (Tristan da Cunha Government, 2021). The MS Oliva shipping accident at Nightingale Island, approximately 20 km from Inaccessible Island and 395 km from Gough Island, in March 2011, resulted in significant damage to wildlife at Nightingale Island and probably some damage to the values of Inaccessible Island (Cuthbert, 2013; Ruoppolo et al., 2013), e.g. by oiling of Northern Rockhopper Penguins, and demonstrates the potential impacts of future accidents at the site.

In October 2020, the MV GeoSearcher (the certified rock lobster fishing vessel) sank off the NW coast of Gough Island, but due to the inaccessibility of the site, the consequences to wildlife and the site's values could not be ascertained.

Chronic pollution from a busy shipping line north of the islands remains a persistent threat. Other less visible pollution has manifested itself as an increase in the mercury content in seabird feathers at Gough Island over 25 years (Becker et al., 2016). Another potential impact on seabirds is light pollution from ships. For example, petrels have been found to become disoriented by artificial lights (Ryan et al., 2021).

IUU fishing, including long-lines, gillnets, and trawls, have the potential to cause significant reductions in populations, but the extent to which these affect species on Gough and Inaccessible Islands is unknown (Cuthbert et al., 2005). Ongoing satellite surveillance has shown that risks of IUU fishing are negligible for most of the year, except for the March to April peak of squid jiggers transiting through the Tristan da Cunha EEZ on route to the Falkland Islands, and May through to July when the southern bluefin tuna fleet operate close to the southern boundaries of the EEZ (Tristan da Cunha Government, 2021). Illegal and legal fishing in the high seas poses one of the most significant threats to the birds at the site, therefore the threat remains high.

House Mice (Mus musculus): Egg and chick predation by predatory house mice, the only invasive rodent on Gough Island, threatens the populations of several terrestrial and seabirds including Tristan Albatross, Atlantic Petrel and MacGillivray's Prion (Cuthbert and Hilton, 2004; Wanless et al., 2012; Davies et al., 2015; Dilley et al., 2015; Jones et al., 2021; Oppel et al., 2022). Mice may have caused a major population decline of the endemic Gough Bunting (Ryan and Cuthbert; 2008; Jones et al., 2020b). Prior to 2021 mice predated roughly 1-3 million seabird eggs and chicks each year on Gough (Caravaggi et al., 2019). Oppel et al. (2022) estimate that the global Tristan albatross population has decreased by ~1% per year from 2004 to 2021 despite the apparent stability of the observed number of breeding pairs on its main breeding island in the South Atlantic Ocean due to the lack of recruitment caused by mouse predation of chicks. This will eventually catch up with the population once long lived adults start to be lost from the population and then the species will potentially decline rapidly (IUCN Consultation, 2025). Mice were also predating breeding adult Tristan and adult Atlantic Yellow-nosed Albatrosses prior to the attempted mouse eradication in 2021 through the Gough Island Restoration Programme (Jones et al., 2019; Connan et al., 2023). The mouse eradication attempt was carried out in the austral winter of 2021, but the operation was not successful and invasive mice therefore remain on Gough Island (Samaniego et al., 2022), which significantly impacts the population of several species. The predatory behaviour of mice attacking seabird chicks has resumed within 2 years after the mouse population had recovered from the 2021 operation. Together with long-line fishing, this may lead to the extinction of MacGillivray's Prion (Jones et al. 2021) and the Tristan Albatross, one of the emblematic species of the site (Wanless et al., 2009). Mice also likely affect the invertebrate fauna of the island (Houghton et al., 2019), but research to investigate invertebrate community composition only started in 2018.

The attempt to eradicate invasive mice in 2021 inadvertently led to the collapse of the endemic Gough moorhen population. Despite a captive population being held to mitigate the mortality expected from rodent bait consumption by moorhens, the released population has not recovered following the operation and the Gough moorhen population on Gough was critically low (<20 birds) in 2025, with evidence for only a single reproductive pair. However, several thousand Gough moorhens likely exist on Tristan da Cunha, where the species was introduced in the 1950s.

Procumbent pearlwort (Sagina procumbens): accidentally introduced to Gough Island in the late 20th Century, and spread rapidly along 500m of coastline near to the Gough meteorological station (Visser et al., 2010). Continued eradication and control efforts, and monitoring for this and other invasives, including New Zealand flax (Phormium tenax) on Inaccessible, are needed to control this continuing threat (UNEP-WCMC, 2011; Ryan et al., 2012). However, the most recent SOC report states that the eradication of the procumbent pearlwort is no longer possible and a containment operation is instead being implemented (UNESCO, 2023).

Other invasive plant species: include Verbena bonariensis, Solanum tuberosum, Juncus effusus Agrostis gigantean, Brassica rapa, and Cynodon dactylon. Additionally, New Zealand flax (Phormium tenax) was introduced to Inaccessible Island in the 1930s and has invaded predominantly the northeastern region of the island (Tristan da Cunha Government, 2024). The Flax Eradication Project has been an ongoing effort facilitated by the Royal Society for the Protection of Birds (RSPB) and managed by the Tristan Conservation Department. The project is ongoing and will need further effort to be successful, although the current technique seems to be working (IUCN Consultation, 2025).

Invertebrate species: The number of introduced invertebrate species (most of them having been introduced since 1950), now exceeds that of native species, at least on Gough Island (Jones et al., 2002). However, the exact extent and impact of these invasions needs to be studied further and this particular point is data deficient. On Inaccessible Island, introduced scale insects and associated sooty mould fungus have reduced Phylica fruit loads and killed trees. As a consequence of this food shortage, the population of Dunn’s Finches (N. acunhae dunnei) has declined by 50% in the last ten years (Ryan et al., 2014; Dilley et al., 2020). Visitation is minimal but strong biosecurity measures are needed. A Horizon Scanning Workshop documents the pathways and identified species that could impact the islands (Roy et al., 2019). Additionally, a biocontrol agent of the scale insect is potentially established on Inaccessible Island, as the establishment has been confirmed on the other 2 northern islands of similar conditions, however this needs to be confirmed (IUCN Consultation, 2024).

Fish species: On 7th June 2006, a decommissioned, semi-submersible petrochemical production platform was shown to be heavily fouled with species alien to Tristan. The alien silver porgy Diplodus argenteus (Sparidae), and a variable blenny (Parablennius pilicornis) have established themselves in great numbers at the Northern islands, although these have not reached Gough Island. This is a Very High Threat, as a decline in the local Klipfish (Bovichtus diacanthus) has already been reported (IUCN Consultation, 2025).

To address the threat posed by invasive species, the Conservation Department has biosecurity measures in place, along with methods to help control and remove invasive species. Additionally, information sheets have been issued to fishing vessels traveling north to south, advising them to discharge ballast water at least 100 miles from Tristan to reduce the risk of introducing invasive species such as the Porgy to Gough (IUCN Consultation, 2025).

Macro- and microplastic pollution has become a threat to the marine and coastal environment of the site (Tristan da Cunha Government, 2021). Plastic items and particles washed up on beaches or present in water can trap, entangle, and be ingested by marine and terrestrial wildlife and cause harm or death. In 2017, a survey by National Geographic found microplastics in 15 out of 19 seawater samples taken from locations around Tristan top islands and Gough, with an average of between 0 to 2.3 pieces of microplastic found per litre (Caselle et al., 2018). Ryan et al. (2024) found that the arrival rate of plastic bottles on Inaccessible Island has doubled since 2018, though the incidence of plastic ingestion by seabirds on Inaccessible remained largely unchanged between 1989 and 2018 (Pérold et al., 2024). Plastic debris can also be a vector for the arrival of invasive species (Barnes et al., 2018). Impacts on individuals or populations, however, are not quantified, though it may impact other heritage values, as is known from other sites (e.g. Henderson Island). Recent work on Nightingale Island which will almost certainly be mirrored on Inaccessible Island showed that over 90% of all Great Shearwaters sampled had life threatening amounts of plastic within chicks and that most dead birds sampled showed that plastic was the most likely if not certain cause of death (IUCN Consultation, 2025).