Black-footed Albatross Diomedea Nigripes Research Articles

Genetic characteristics of the Black-footed Albatross Diomedea nigripes on the Bonin Islands and their implications for the species' demographic history and population structure

The Black-footed Albatross Diomedea nigripes is an endangered seabird that is endemic to the North Pacific. The genetic structure of Black-footed Albatross populations on three of the Hawaiian Islands and on Izu-Torishima Island, Japan, has been studied previously, using the mitochondrial cytochrome b region. Hawaiian and Japanese breeding groups are genetically different, and the genetic diversity of the birds on Izu-Torishima is lower than that of birds in the Hawaiian Islands. We analyzed 50 Black-footed Albatrosses from the Bonin Islands, where a relatively stable population persisted throughout the twentieth century. Although albatrosses in the Bonin Islands do not differ significantly from those on Izu-Torishima in their cytochrome b region sequences, they do exhibit higher genetic diversity (as high as those from the Hawaiian colonies). A statistical parsimony network revealed two clades, one primarily in the western North Pacific colonies and the other primarily in eastern North Pacific colonies. The total network appears as a dumbbell-shaped phylogeny, suggesting recent population expansion in both populations, although the population breeding in the western North Pacific is only about 5% of the size of that in the eastern North Pacific. Our results suggest that Black-footed Albatrosses in the Bonin and the Hawaiian Islands differ genetically but are comparable natural biological units for conservation and management purposes.

The foraging ranges of Black-footed Albatross Diomedea nigripes breeding in the Bonin Islands, southern Japan, as determined by GPS tracking

The foraging movements of six Black-footed Albatross Diomedea nigripes (an endangered species) breeding in the Mukojima Islands (a subset of the Bonin Islands) were successfully tracked over a period of two weeks using back-mounted global positioning system (GPS) data loggers (GDBL-II) during the nest-guarding period. Ninety percent of foraging was done over relatively shallow waters within 200 km of the breeding site. The population of this species in the Bonin Islands has not decreased during last ten years, while the area of long-line fishing is likely to overlap with the albatross foraging area around the islands. The effect on population should be assessed carefully.

Arsenic accumulation in livers of pinnipeds, seabirds and sea turtles: subcellular distribution and interaction between arsenobetaine and glycine betaine

Concentrations of total arsenic and individual arsenic compounds were determined in liver samples of pinnipeds (northern fur seal Callorhinus ursinus and ringed seal Pusa hispida), seabirds (black-footed albatross Diomedea nigripes and black-tailed gull Larus crassirostris) and sea turtles (hawksbill turtle Eretmochelys imbricata and green turtle Chelonia mydas). Among these species, the black-footed albatross contained the highest hepatic arsenic concentration (5.8±3.7 μg/g wet mass). Arsenobetaine was the major arsenic species found in the liver of all these higher tropic marine animals. To investigate the cause of high accumulation of arsenobetaine, subcellular distribution of arsenic and relationship between arsenobetaine and glycine betaine concentrations were examined in the livers of these animals. There was no relationship between total arsenic concentration and its subcellular distribution in liver tissues. However, a significant negative correlation was found between arsenobetaine and glycine betaine concentrations in the liver of six species examined. This result may indicate that arsenobetaine is accumulated in these marine animals as an osmolyte along with glycine betaine, which is a predominant osmolyte in marine animals because the chemical structure and properties of arsenobetaine are similar to those of glycine betaine.

Sea-bird aggregation at a deep North Pacific seamount

During June 1991, we studied sea birds at a mid-ocean seamount (Fieberling Guyot) in the eastern North Pacific Ocean. Avifaunal composition changed from small Procellariiformes [a storm-petrel; Oceanodroma leucorhoa (Vieillot)] away from the seamount to an assemblage dominated by larger tubenoses [mostly black-footed albatross Diomedea nigripes Audubon and Cook's petrel Pterodroma cookii (Gray)]. Compared to adjacent waters, sea-bird density and biomass within a 30-km radius centered on the seamount summit were 2.4 and 8 times higher, respectively. Individual sea-bird taxa were 2 to 40 times more abundant at the seamount relative to values reported previously from large-scale surveys of deep-ocean regions in the central North Pacific. In September 1991 we studied potential prey of sea birds in the upper water column using a neuston net and multiple opening-closing net system (MOCNESS) tows. Most potential prey types in the neuston exhibited no significant enhancement over the seamount. MOCNESS samples at 10 m depth, however, showed several prey types to be more abundant over the seamount, and the dominant size class of fish was slightly larger. We attribute the sea-bird aggregation observed at this seamount to changes in the abundance and/or behavior of pelagic organisms in the deep scattering layer (not adequately sampled in this study), perhaps augmented by migrations of seamount residents into the surface layers. Processes on and in the vicinity of seamounts may provide spatially-predictable prey to wide-ranging aerial sea birds foraging in this relatively austere environment.