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Site description (2012 baseline):

Rose Atoll consists of two small islets (Sand Island - 2.5 ha and Rose Island - 5.2 ha), covering six hectares of emergent land and 15,878 ha of submerged reef (Wegmann & Holzwarth 2006), and is the only uninhabited island in American Samoa. Rose is the easternmost island of Samoa and is situated 120 km east-southeast of Ta’u Island (Wegmann & Holzwarth 2006). Rose is one of the smallest atolls in the world, it is almost square with sides of approximately 1.5 miles and it encloses a lagoon of 2 km across at the widest point. Rose Island is permanently vegetated, although Sand Island is only vegetated intermittently (it is frequently cleared by hurricanes) (Rodgers et al. 1992). The reef is made mostly of coralline algae, as opposed to coral, and therefore is quite unusual (Wegmann & Holzwarth 2006). The atoll became a National Wildlife Refuge under the US Fish and Wildlife Service (USFWS) in 1973 and it is home to 11 species of migratory seabird, as well as the threatened green sea turtle. Rose Atoll receives far less precipitation than the majority of American Samoa because of its low elevation: hurricanes are frequent (Wegmann & Holzwarth 2006).

Rose Atoll is a key migratory stopover for at least seven seabird species (Wegmann & Holzwarth 2006) and approximately 97% of the seabird population of American Samoa resides on Rose (USFWS 2010). The Sooty Tern dominates population numbers on Rose Atoll. Abundances of several hundred thousand have been recorded frequently (400,000 in 1974, 300,000 in 1975 (Amerson et al. 1982)). However, little quantitative data has been documented for this species on Rose more recently. Black Noddies have usually been observed in the hundreds (235 in 1980, (Amerson et al. 1982) 292 in 1988 and 583 in 2005 (Wegmann & Holzwarth 2006)) and are most often found in nests in high up Pisonia branches (Amerson et al. 1982). Red-footed Boobies have been recorded in similar numbers, although their populations have shown greater fluctuation (3500 in 1975 (Amerson et al. 1982), 450 in 1984 and 142 in 2002 (Wegmann & Holzwarth 2006). Rose is one of only three nesting sites for Red-footed Boobies in American Samoa (Amerson et al. 1982). The activity of tree nesting seabirds such as Black Noddies and Red-footed Boobies could be adapted to significant but non-catastrophic disturbances, explaining their observed tolerance to hurricanes and the Pisonia die-off (Wegmann & Holzwarth 2006). Brown Boobies are common, and at its peak, the Brown Booby population on Rose Atoll may be the largest and densest in the Central and South Pacific (possibly with the exception of Palmyra in the Line Islands) (Amerson et al. 1982). Masked Boobies have been common on Rose Atoll (540 in 1974, 200 in 1976 (Amerson et al. 1982), although the numbers recorded more recently have been much lower (15 in 1989, 18 in 1991, 12 in 1998 (Wegmann & Holzwarth 2006)). The ground nesting Brown Noddy is also found on Rose (143 in 1982, 148 in 1991 and 111 in 2002 (Wegmann & Holzwarth 2006)). Common White Terns breed on all islands in American Samoa and although previously common, sightings have declined more recently (550 in 1975 (Amerson et al. 1982), 75 in 1984, 63 in 2002 (Wegmann & Holzwarth 2006)). Breeding of the species has been recorded mostly from September/October to February (southern summer) (Amerson et al. 1982). Rose Atoll is the Greater Frigatebird’s major nesting site in American Samoa (Amerson et al. 1982). Abundances tend to be in the hundreds (200 in 1970, 300 in 1974, 750 in 1976 (Amerson et al. 1982). Nesting has been recorded in June and October (Amerson et al. 1982). The Lesser Frigatebird is also common on Rose (200 in 1975, 425 in 1976 (Amerson et al. 1982). Grey-backed Terns are relatively uncommon across the whole of American Samoa, with the total population estimated at less than 200 (Amerson et al. 1982). A small number have been observed on Rose Atoll (14 in 1976 (Amerson et al. 1982)). Red-tailed Tropicbirds are also present in small numbers (40 in 1976 (Amerson et al. 1982), 27 in 1990 and 26 in 2005 (Wegmann & Holzwarth 2006)). Between 1976 and 1991 there were a small number of sightings of vagrant, off-course migratory birds, most commonly the Long-tailed New Zealand Cuckoo (Wegmann & Holzwarth 2006).

Non-bird biodiversity: The lagoon hosts a diverse array of marine life, including a population of rare giant clams and a number of fish species (Wegmann & Holzwarth 2006). The vegetation on Rose is dominated by the Tournefortia argentea shrub. The previously extensive Pisonia forest has significantly declined since the end of the 20th Century (Wegmann & Holzwarth 2006). Strawberry Hermitcrabs gather under vegetation during the day and forage across the island at night (Wegmann & Holzwarth 2006).

The atoll is currently uninhabited by humans and there is no evidence of prehistoric occupation by Samoans. Human use of the atoll is believed to have begun in 1920 with the plantation of Coconut Palms on Rose Island. During the Second World War, Rose was a designated US Naval Defence Area, but never saw military activity (Wegmann & Holzwarth 2006).

Rose Atoll’s terrestrial environment has a crest of no more than 5m above sea level, and is at risk of severe physical changes as a result of climate change and sea-level rises. Predicted consequences include: increased inundation and flooding, rapid coastal erosion, the introduction of seawater into groundwater, increased ground and sea-surface temperatures (MacLean 2001). Biological implications range from ‘moderate’ to ‘severe’ (Baker et al. 2006) for the atoll’s emergent land, jeopardising seabird populations as well as numerous other plants and animals (Wegmann & Holzwarth 2006). Rose Atoll shows an infestation of Coconut Palms and the population boomed after Hurricane Olaf in 2005 and the uprooting of many native canopy trees (Wegmann & Holzwarth 2006). The atoll’s native Pistonia forest vegetation is not only at risk from Coconut Palm but it has also been targeted by alien species of ant and scale insect since the late 1990s and few healthy trees remain (USFWS 2010). This homogenisation of vegetation was predicted to severely reduce the atoll’s value as a seabird nesting site (Wegmann & Holzwarth 2006). However, effects of this kind have not yet been observed, with the tree-nesting Black Noody and Red-footed Booby populations unaffected from 1991-1998 (Wegmann & Holzwarth 2006). Similarly, the changing Pisonia population has not changed Red-tailed Tropicbird nesting activity, suggesting that although it may prefer the covered nests of the Pisonia tree, this is not essential (Wegmann & Holzwarth 2006). Sandbur, a highly invasive grass species, had been observed on Rose on four occasions in 1994. However the McDermond et al. (1994) expedition fixed a black tarpaulin over the infested area, successfully eradicating the Sandbur, and it has not been observed since (Wegmann & Holzwarth 2006). The Black Rat was introduced to the island in c.1920 (Wegmann & Holzwarth 2006). An eradication programme began in 1990, performed by the USFWS, and all rats (a population of 1048 in 1990 before the programme began) were removed by 1991 (Wegmann & Holzwarth 2006). Prior to this eradication, the rat population on Rose was believed to have had an unmeasured but likely harmful effect on seabird recruitment and nesting activity (inferred from data of islands in similar situations) (Wegmann & Holzwarth 2006), including preying on eggs, chicks and adults of all breeding seabirds, but particularly ground nesting species and destroying nest-making vegetation (USFWS 2005). Polynesian rat is documented as being reported and controlled in 2004 by the Island Conservation and Ecology Group (www.issg.org). Scale insect infestations have been documented since 2002 and these contribute to Pisonia mortality (Wegmann & Holzwarth 2006, USFWS 2010). There are established quarantine procedures to prevent the introduction of invasive species, although visits that do not abide by these regulations are known to take place (Wegmann & Holzwarth 2006). The Jin Shiang Fa longliner ran aground on the Rose Atoll barrier reef in October 1993, releasing 100,000 gallons of diesel. This had a significant impact on the marine environment, destroying coral and algal reef structures (Margos 1994). The metal structure of the boat fragmented, scattering debris across the reefcrest and forereef. This did not simply affect the coral reef, but four years later an invasive algal bloom was discovered, which had been sparked by the exceptionally high levels of iron in the water from the wreck (Wegmann & Holzwarth 2006). Human disturbance and direct harvesting of seabirds are listed as threats to 26 and 23 of the 97 globally threatened seabirds respectively (Croxall et al. 2012). For Near Threatened and Least Concern species it is likely that human disturbance and consumption affect an even greater proportion, particularly of tropical species, for which major reductions in populations and/or breeding sites are increasingly indicated but seldom quantified, especially across the whole range of the many wide-ranging tropical seabird species (Croxall et al. 2012). Human disturbance (such as recreational activities) and direct harvesting sometimes occurs at this site. Trespassing has been inferred from litter on the island (Ludwig 1982, Barclay 1992). The sustainability of such harvests is unknown but it may represent a threat to this population.

Management of Rose Atoll is shared by the USFWS and the government of American Samoa, Department of Marine and Wildlife Resources (DMWR) (Wegmann & Holzwarth 2006). The boundary of the refuge site reaches three miles around the atoll. Scientists and managers from a multitude of organisations and federal agencies (USFWS, American Samoa DMWR, the National Park Service (National Park of American Samoa), the National Oceanic and Atmospheric Administration (NOAA; Pacific Island Fisheries Science Centre) have carried out both terrestrial and marine habitat monitoring since the atoll was made a Wildlife Refuge in 1973. In 1993, the USFWS and the American Samoan government entered into a Memorandum of Understanding, to encourage coordination and cooperation so that information about the island could be developed and the wildlife of Rose managed more effectively (Wegmann & Holzwarth 2006).

Since its recognition as a wildlife refuge in 1973, public access has been denied and visits have been restricted to those with a special use permit (Wegmann & Holzwarth 2006). A new draft management plan was completed in 2012 to be finalised soon (http://www.fws.gov/roseatoll/planning.html)

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Recommended citation
BirdLife International (2024) Important Bird Area factsheet: Rose Atoll (American Samoa). Downloaded from https://datazone.birdlife.org/site/factsheet/rose-atoll-iba-american-samoa on 23/11/2024.