Current view: Text account
Site description (2012 baseline):
Pressure/threats to key biodiversity
Seabirds and commercial fisheries that harvest the same prey are affected mutually by their food supply. The consequences of this two-way interaction on seabird populations are complex and poorly quantified. Removal of predatory fish by commercial fisheries can lead to an abundance of prey fish and a subsequent increase in food availability for seabirds (Birdlife International 2008). However, fisheries that now target lower tropic levels have reversed this relationship (Birdlife International 2008, Bertrand et al. 2008, Cury et al. 2011). In the Pacific the most widespread and abundant nekton-feeding seabirds such as Wedge-tailed Shearwater (Puffinus pacificus), Sooty Tern (Sterna fuscata), and Red-footed Booby (Sula sula) all feed at or close to the surface, where they are largely dependent on predatory tunas (Thunnus spp.) to drive smaller prey fish to the surface (Ballance et al. 1997). Whereas the seabirds themselves do not consume any tuna, the impact of commercial fisheries on tuna populations could affect seabirds indirectly by diminishing the tuna schools, and so reducing available prey patches for the seabirds (Brooke et al. 2006). This potential impact is not currently recognized in tuna management decisions (Brooke et al. 2006). The total extent of decline in adult biomass of tuna populations in the Pacific Ocean is 49.2% since industrial fisheries began in the 1950s (Juan-Jordáa et al. 2011) suggesting the availability of accessible prey patches for seabirds may have declined over this period. A further interaction comes from discards from commercial fisheries that can provide additional food for seabirds artificially elevating populations (Jodice et al. 2011). The overall relationship between these interactions is not know. Commercial fisheries are recognised as being a potential threat to seabird populations within this site due to the presence of commercial trawl and long-line fishing vessels operating in the Marshall Islands EEZ (Gillett, 2011).
Incidental mortality through accidental bycatch in fisheries is a known threat to seabird populations (Croxall et al. 2012) and is the most critical global threat to most species of albatrosses and large petrels (Gales 1998, Brothers et al. 1999, Gilman et al. 2005). Bycatch of Laysan Phoebastria immutabilis and Black-footed Albatross P. nigripes in the Hawaii pelagic tuna and swordfish longline fishery is a conservation concern, but mitigation measures are being introduced to try to reduce its impact (Gilman et al. 2008). Trawl fisheries are also known to cause significant levels of bycatch, again to larger seabird species such as albatrosses and gannets (BirdLife International 2008; Watkins et al. 2008). Gillnet fisheries are also known to cause substantial mortality amongst pursuit-diving seabird species, which are the most vulnerable to entanglement (BirdLife International 2010). There is minimal documented information on bycatch of seabirds in tropical fisheries, and nothing about population-level impacts on terns, tropicbirds, boobies, frigatebirds and small-petrels in the tropical Pacific or within this site. Further information is needed about this potential threat but we precautionarily list it at this site due to the presence of commercial trawl and long-line fishing vessels operating in the Marshall Islands EEZ (Gillett, 2011).
Ingestion of plastic debris at sea by seabirds has increased since the 1970s, particularly among the Procellariiformes, resulting in a range of lethal and sub-lethal side effects (Carey 2011). However, the population level impacts of this form of ocean pollution have not yet been quantified, nor has the overlap between high-use areas of foraging seabirds and spatial distribution of plastic pollution been assessed. The amount of plastic waste in the marine environment is increasing, as is ingestion by seabirds. Although the level of threat this poses to seabirds at this site is un-quantified, marine plastics are likely to be an insidious threat.
Major sources of artificial light in the marine environment include vessels, lighthouses, light-induced fisheries, offshore mining operations, oil/ gas platforms. Seabirds are highly visually oriented and known to become disorientated at night in the presence of artificial light (Bruderer et al., 1999). Depending on the weather, season, the age of the birds and the lunar phase seabirds can be attracted to light risking collision with vessels or oil/gas platforms (Montevecchi, 2006). A few cases of mass collisions of hundreds or thousands of seabirds with vessels have been documented (Black, 2005; Ryan, 1991; Dick and Davidson, 1978), but otherwise, surprisingly little quantitative information is available about light-induced bird strikes at sea. The potential population-level impacts of light-induced mortality at this site have not been quantified but it may pose a threat due to the operation of commercial fishing vessels in Marshall Islands EEZ (Gillett, 2011).
Recommended citation
BirdLife International (2024) Important Bird Area factsheet: Bikar Atoll Marine (Marshall Islands). Downloaded from
https://datazone.birdlife.org/site/factsheet/bikar-atoll-marine-iba-marshall-islands on 23/11/2024.
