Wildlife of
Saint Helena, Ascension and Tristan da Cunha

Primary Threats

• Invasive mammals and plants are among the most severe pressures. On Saint Helena, invasive vegetation (e.g., aggressive non-native plants) and introduced invertebrates have altered habitats and outcompeted endemic flora in the remaining fragments of native cloud-forest and scrub. On Tristan da Cunha (including Gough Island), invasive mice have caused catastrophic breeding failures in some seabirds by preying on chicks, and biosecurity is critical to prevent new introductions. Ascension has a history of invasive predators and habitat modification; although feral cats were eradicated, ongoing biosecurity is needed to protect seabirds and turtle nesting beaches.
• Native terrestrial habitats are naturally limited by island size and have been historically reduced or degraded by past land clearance, grazing and invasive plants. On Saint Helena, endemic-rich habitats persist as small, fragmented remnants (e.g., cloud-forest on high peaks) requiring active restoration and fencing/control to prevent further decline. On Ascension, much of the lowland is naturally arid and sensitive; disturbance and non-native vegetation change available nesting habitat for seabirds. On Tristan, settlement is concentrated, but sensitive coastal and upland areas can be affected by localized land use and introduced grazers.
• Warming seas and shifting ocean productivity can affect food availability for wide-ranging seabirds (albatrosses, petrels, terns) and marine predators that rely on predictable prey. Sea-level rise and changes in storm frequency/intensity threaten low-lying seabird nesting sites and Ascension's turtle nesting beaches, while altered rainfall patterns can stress Saint Helena's already limited freshwater and cloud-forest moisture regimes. Climate variability also compounds recovery efforts for small endemic plant populations.
• The territory's vast EEZs are difficult to patrol, increasing vulnerability to illegal, unreported and unregulated (IUU) fishing and broader regional fishing pressure on tuna and associated pelagic ecosystems. Tristan's economy is heavily linked to the rock lobster fishery; while managed, it remains sensitive to stock declines, climate-driven shifts and market pressures. Maintaining effective monitoring and enforcement over remote waters is a continuing challenge, especially where MPA rules require surveillance capacity.
• Marine plastic and lost fishing gear accumulate on remote South Atlantic shores, affecting seabirds through ingestion/entanglement and degrading coastal habitats. Local waste management constraints typical of small, isolated islands can make disposal and recycling difficult. Shipping-associated risks (oil spills, operational discharges) are a concern because supply routes are long and response resources are limited.
• On small islands, even modest infrastructure can have outsized impacts. The Saint Helena airport and associated roads and development can increase erosion, introduce invasive species via cargo pathways, and expand human footprint into sensitive areas if not carefully managed. On Ascension, facilities linked to communications/defence and settlement can disturb nearby nesting areas and increase light pollution that affects seabirds. Port facilities and moorings can affect nearshore habitats and raise biosecurity risks.
• Wildlife is often concentrated at accessible coastal colonies and beaches. Disturbance from visitors, vehicles, pets, and artificial lighting can disrupt seabird breeding and affect turtle nesting success on Ascension. On Saint Helena, recreational access to fragile endemic plant sites can cause trampling and seed spread of invasive plants without strong site management.
• Remote islands have limited veterinary/laboratory capacity, making early detection and response difficult. There is ongoing concern that pathogens such as avian influenza could reach dense seabird colonies (especially on Tristan/Gough), where outbreaks could have rapid, severe impacts. For Saint Helena's highly restricted endemic flora, new plant pests or diseases introduced through imports could threaten already small populations.
• Many endemic species occur in extremely small, isolated populations (especially Saint Helena's endemic plants and invertebrates), increasing risks from inbreeding, low genetic diversity and demographic instability. Single-site populations are also vulnerable to random events (storms, droughts, landslides) that can eliminate a large fraction of remaining individuals.
• Historic and ongoing changes such as grazing pressure, altered fire regimes, and erosion have modified natural vegetation structure and soils, particularly on Saint Helena where steep slopes and past land use can accelerate sediment loss. On Ascension, introduced vegetation and soil changes alter natural arid-land processes, affecting nesting habitat suitability for native fauna.
• Freshwater availability is limited and climate-sensitive, particularly on Saint Helena where drought periods can stress ecosystems and constrain restoration (tree planting, nursery propagation). Dependence on imported materials and fuels can also complicate sustained conservation operations and rapid response to environmental incidents.