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.