The U.S. Geological Survey, Biological Resources Discipline has recently published a formal status assessment of Laysan Phoebastria immutabilis and Black-footed P. nigripes Albatrosses. In response to the growing concerns over the impacts of these threats on albatross populations, the U.S. Fish and Wildlife Service contracted with the U.S. Geological Survey to conduct an assessment of Laysan and Black-footed Albatross populations. This assessment includes a review of the taxonomy, legal status, geographical distribution, natural history, habitat requirements, threats, and monitoring and management activities for these two species. The second part of the assessment is an analysis of population status and trends from 1923 to 2005.
The assessment found that over the past century, Black-footed and Laysan Albatrosses have been subjected to high rates of mortality and disturbance at their breeding colonies and at sea. Populations were greatly reduced and many colonies were extirpated around the turn of the 20th century as a result of feather hunting. At sea, thousands of Laysan and Black-footed Albatrosses were killed each year in high-seas driftnet fisheries, especially from 1978 until the fisheries were banned in 1992. During the 1990s, other anthropogenic factors, such as predation by non-native mammals and exposure to contaminants, also were documented as reducing productivity or increase mortality.
The primary threats to Laysan and Black-footed Albatrosses include interactions with commercial fisheries, predation by introduced mammals, reduced reproductive output due to contaminants, nesting habitat loss and degradation due to human development and invasive plant species, and potential loss and degradation of habitat due to climate change and sea-level rise. Incidental mortality (bycatch) in commercial fisheries is the greatest anthropogenic source of mortality for both species. The researchers found that longline fishing effort prior to the 1980s was greater than previously estimated and a very significant source of mortality.
The researchers also evaluated the status and trends of Laysan and Black-footed Albatross populations using linear regression, population viability analysis (PVA), and age-structured matrix models. Analyses were predominantly based on nest-count data gathered at French Frigate Shoals, Laysan Island, and Midway Atoll. At these three colonies, nest counts were greater than 75% of the World's population of Black-footed albatrosses and greater than 90% of Laysan Albatrosses.
The Laysan Albatross population increased from an estimated 18 000 pairs in 1923 to 590 000 pairs in 2005. The large population increase during the past 83 years is likely a response to the end of persecution by feather hunters, decrease in conflicts with military activities, and an increase in nesting areas at some colonies. The population showed a positive change over 1923 to 2005 and 1957 to 2005 and a stable size from 1992 to 2005. The Laysan Albatross population, summed across all three colonies (Midway Atoll, Laysan Island, and French Frigate Shoals), increased 6.7% a year from 1992 to 2005, and the estimated bycatch of 2500 birds per year is less than the estimated Potential Biological Removal (PBR)-the maximum number of mortalities, not including natural deaths, while maintaining an optimum sustainable population.
The Black-footed Albatross population increased from an estimated 18 000 pairs in 1923 to 61 000 pairs in 2005. As with Laysans, the increase in the Black-footed Albatross population over the past 83 years probably is in response to the end of persecution at breeding sites. Trends in population size showed a positive change from 1923 to 2005, no change from 1957 to 2005, and no change from 1998 to 2005. The Black-footed Albatross population is stable, or slightly increasing, with a population growth rate of 0.3% a year. The 2005 estimate of bycatch is 5228 birds a year, but if this value is doubled, a safeguard for underestimating bycatch, it approaches the PBR of 11 980 birds per year, although the upper 95% confidence limit (17 486) exceeds the PBR.
Researchers found their knowledge of interactions of Laysan and Black-footed Albatrosses with fishing operations is imperfect, partly because of the difficulty of obtaining reliable bycatch data from all fleets. Results from the modelling indicate that fishery bycatch is not significantly affecting the size of the Laysan Albatross population, but may be causing a decrease in Black-footed Albatross populations.
Arata, J.A., Sievert, P.R. & Naughton, M.B. 2009. Status assessment of Laysan and black-footed Albatrosses, North Pacific Ocean, 1923-200. U.S. Geological Survey Scientific Investigations Report 2009-5131. 80 pp. The document can be downloaded from the USGS website (click here).
Lindsay Young, ACAP North Pacific News Correspondent, 21 September 2009