Skip Links

USGS - science for a changing world

Scientific Investigations Report 2009–5131

Status Assessment of Laysan and Black-Footed Albatrosses, North Pacific Ocean, 1923-2005

By Javier A. Arata, University of Massachusetts-Amherst, Paul R. Sievert, U.S. Geological Survey, and Maura B. Naughton, U.S. Fish and Wildlife Service

Thumbnail of and link to report PDF (10.4 MB)Executive Summary

Over the past century, Laysan (Phoebastria immutabilis) and black-footed (Phoebastria nigripes) albatrosses have been subjected to high rates of mortality and disturbance at the 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. Populations were recovering when military occupation of several breeding islands during World War II led to new population declines at these islands and additional colony extirpations. 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. Through the 1990s, there was a growing awareness of the large numbers of albatrosses that were being killed in longline fisheries. During the 1990s, other anthropogenic factors, such as predation by non-native mammals and exposure to contaminants, also were documented to reduce productivity or increase mortality.

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, geographic 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.

Laysan and black-footed albatrosses forage throughout the North Pacific Ocean and nest on tropical and sub-tropical oceanic islands from Mexico to Japan. As of 2005, 21 islands support breeding colonies of one or both species. The core breeding range is the Hawaiian Islands, where greater than 99 percent of the World’s Laysan albatrosses and greater than 95 percent of the black-footed albatrosses nest on the small islands and atolls of the Northwestern Hawaiian Islands. These islands are all protected as part of the Papahānaumokuākea Marine National Monument.

Albatrosses are long-lived seabirds with deferred maturity, low fecundity, and high rates of adult survival. Their life history characteristics make populations especially vulnerable, to small increases in adult 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 (post-fledging) for both species. We found that longline fishing effort prior to the 1980s was greater than previously estimated and a very significant source of mortality.

Regulations to minimize and monitor albatross mortality have been enacted in most U.S. and Canadian longline fisheries, but monitoring of bycatch rates and regulations to minimize seabird mortality are extremely limited in the much larger multinational longline fleets. Management to address threats at the breeding colonies is ongoing and includes eradication or control of non-native species, habitat management, and abatement programs to reduce impacts of contaminants. Effective long-term conservation and management of the Laysan and black-footed albatrosses require management and monitoring at the breeding colonies and at sea and continued assessment of population status and trends.

We 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 percent of the World’s population of black-footed albatrosses and greater than 90 percent of the World’s population of Laysan albatrosses. The first quantitative estimates for most colonies were made in 1923, after the era of feather hunting, when populations were at their lowest levels. Another comprehensive survey of Hawaiian colonies was conducted between 1956 and 1958, after which colony counts were irregular until the U.S. Fish and Wildlife Service (USFWS) began standardized surveys of French Frigate Shoals in 1980, and Laysan Island and Midway Atoll in 1992. Regression analysis was used to evaluate linear trends in populations from 1923 to 2005, 1957 to 2005, and 1992 to 2005. PVA was conducted by fitting stochastic, discrete-time, logistic, and exponential models to observed data and then making population projections 60 years (about three generations) into the future. Age-structured population models, based on a matrix modeling framework, were used to evaluate the effect of fishery bycatch on populations. Estimates of albatross bycatch were either obtained by projecting measured rates for U.S. fisheries to International fleets or by using published values.

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. Analysis of linear trends in the population showed a positive change over 1923 to 2005 and 1957 to 2005 and a stable size from 1992 to 2005. PVA results for the Laysan albatross colony on French Frigate Shoals indicate that this colony is currently stable, but there is a 28-percent probability of the population decreasing by 24 percent over the next 60 years. PVA results for the Laysan Island colony indicate that the colony is most likely to increase in size over the next 60 years, but there also is a 45-percent probability of the colony decreasing in size. PVA was not conducted for Midway Atoll due to the small sample size. Matrix modeling results indicate that the Laysan albatross population, summed across all three colonies (Midway Atoll, Laysan Island, and French Frigate Shoals), increased 6.7 percent per year from 1992 to 2005, and the estimated bycatch of 2,500 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 Laysan albatrosses, the increase in the black-footed albatross population over the past 83 years probably is in response to the end of persecution at nesting colonies. Analysis of linear 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. PVA results for the black-footed albatross colony on French Frigate Shoals indicate that this colony has a 50-percent probability of increasing by 74 percent in the next 60 years, but it also has a 35-percent probability of significantly decreasing. PVA results for the Laysan Island colony indicate that the population is most likely to increase by 54.7 percent over the next 60 years, but also has a 35-percent probability of significantly decreasing. PVA results for the Midway Atoll colony indicate that it is most likely to increase by 36 percent over the next 60 years, and has a 23-percent probability of decreasing. Matrix modeling results indicate that the black-footed albatross population, summed across all three colonies, is stable, or slightly increasing, with a population growth rate of 0.3 percent per year. The 2005 estimate of bycatch is 5,228 birds per 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-percent confidence limit (17,486) exceeds the PBR.

Our 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 matrix modeling 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.

For additional information contact:
U.S. Geological Survey
Massachusetts Cooperative Fish and Wildlife Research Unit
Department of Natural Resources Conservation
160 Holdsworth Way
University of Massachusetts Amherst
Amherst, MA 01003-9285
Austin, Texas 78754-4733
psievert@nrc.umass.edu

Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.


Suggested citation:

Arata, J.A., Sievert, P.R., and Naughton, M.B., 2009, Status assessment of Laysan and black-footed albatrosses, North Pacific Ocean, 1923–2005: U.S. Geological Survey Scientific Investigations Report 2009-5131, 80 p.



Contents

Executive Summary

Introduction

Taxonomy

Legal and Conservation Status

Species' Descriptions

Geographic Distribution

Natural History

Habitat Requirements

Threats

Monitoring and Management Activities

Population Status and Trends

Conclusions

Acknowledgments

References Cited

Appendix A. Bycatch Estimation

Appendix B. Descriptions and History of the Northwestern Hawaiian Islands

Appendix C. Detailed Methods for Analysis of Population Trends and Bycatch Impacts

Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http:// pubs.usgs.gov /sir/2009/5131/index.html
Page Contact Information: GS Pubs Web Contact
Page Last Modified: Thursday, 10-Jan-2013 19:32:45 EST