JFM 2001 Quarterly Rpt. sidebar
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(Quarterly
Report for Jan-Feb-Mar 2001)
Figure 1. Satellite determined positions of
four Steller sea lions
instrumental with satellite-linked time-depth
recorders.
Juvenile
Steller Sea Lion Winter Capture Trip
Determining the foraging behavior and health status
of juvenile Steller sea lions was the focus of a
capture trip undertaken jointly by scientists from
the AFSC and the Alaska Department of Fish and Game
(ADF&G) from 26 February to 15 March 2001.
The U.S. Fish and Wildlife Service
research vessel Tiglax transported the AFSC
crew from Dutch Harbor to Kodiak Island, where
10 juvenile sea lions were captured and instrumented
with satellite-linked time-depth recorders. An
additional 13 juveniles, mostly 9-month olds, were
captured by ADF&G and AFSC staff in waters off
Kodiak Island. These sea lions were captured
in areas that overlap with local ecosystem studies
being conducted by the Gulf Apex Predator project of
the University of Alaska, Fairbanks. The
quality of telemetry data received to date from
these instruments has been excellent and shows a
variety of behaviors (some positions received from
four sea lions captured at Kodiak Island are shown
in Figure 1 above). In addition to
instrumenting the animals, the field crew collected
a suite of samples and measurements to facilitate
genetic population identification and to determine
individual health and condition.
By Brian Fadely.
Steller Sea Lion Data
Available on Web
New Steller sea lion data and related information is
available to the public on the NMML Web site at
http://nmml.afsc.noaa.gov/
AlaskaEcosystems/sslhome/stellerhome.html.
Databases of pup and adult Steller sea lion counts
are available, as was well as an extensive list of
Steller sea lion literature and presentations from a
recent program review.
Gray Whale Census
NMML staff conducted systematic counts of gray
whales migrating past the Granite Canyon research
station from 013 December 2000 to 5 March 2001.
This shore-based site on the coast of central
California has been used for NMFS surveys since
1974. One or two observers at a time maintained
independent searches for 3 hours each, rotating
through most daylight hours. Double counts
provided data that characterize each observer’s
performance relative to the other’s and can be
used to estimate the proportion of whales missed
within the viewing range, including corrections as a
function of distance. Fix-mounted 25-power
binoculars were used to document the offshore
distribution of whale sightings relative to other
years.
Although the timing of the southbound migration of
gray whales has been very regular since the last
major oceanographic regime shift in the 1970s, in
2000/01 the timing was unusual. In a typical
year, the sighting distribution can be represented
by a symmetrical bell-shaped curve with almost no
whales seen prior to mid-December and after
mid-February. However, in 2000/01, sighting
rates were lower than expected in December, rising
almost exponentially until they peaked in
mid-January (when sighting rates typically peak).
This was followed by an unpatterned period of high
and low sighting rates through February. Rates
finally dropped off after the first week in March (3
weeks later than ever seen before). Analyses with
standardized correction factors are currently
underway to estimate the abundance of the gray whale
population.
By Dave Rugh.
Abundance, Distribution,
and Diet of Bearded and Ringed Seals Near DeLong
Mountain Terminal
The U.S. Army Corps of Engineers is preparing an
environmental impact statement (EIS) for the
possible expansion of the DeLong Mountain Terminal,
a loading facility north of Kotzebue, Alaska, where
ore concentrate from the Red Dog Mine is exported.
As part of the EIS, NMML’s Polar Ecosystems
Program was requested to provide information about
the abundance, distribution, and diet of seals near
the DeLong Mountain Terminal. The coastal zone
between Kotzebue and Kivalina, Alaska, is a
traditional seal hunting area for the Alaska Natives
living nearby. A report describing the results
of NMML’s investigations was completed during the
past quarter, and has been submitted to the Corps of
Engineers for their review.
Aerial surveys of bearded seal (Erignathus
barbatus) and ringed seal (Phoca hispida)
populations were conducted in coastal and offshore
Chukchi Sea waters in May and June 2000. The
surveys were designed to assess the densities of
bearded and ringed seals in the vicinity of the
DeLong Mountain Terminal (Portsite) and Kivalina,
Alaska. Survey lines were flown during mid-day
(1000-1600 local time) at an altitude of 300 ft (91
m) and a speed of 100 knots (185 km/h) along 20 nmi
(37 km) tracklines perpendicular to the shoreline.
In addition, several longer lines of 80-100
nmi (148-185 km) were flown offshore to assess how
coastal densities of seals changed as a function of
distance from shore. Aerial surveys indicated
that bearded and ringed seals were relatively common
in coastal areas. The highest densities of
both species of seals in the survey area were found
in coastal waters south of Kivalina. Bearded seals
were generally more abundant farther from shore,
with the exception of the high densities observed
south of Kivalina; ringed seal densities decreased
as distance from shore increased. A minimum of
55,220 ringed seals and 2,430 bearded seals were
estimated to utilize ice habitats in the vicinity of
the Portsite survey area during May-June 2000.
To investigate the diet of bearded and ringed seals
in the Portsite area, stomach and colon samples
were obtained from Alaska Native subsistence
hunters. A total of four bearded seal samples
(stomach only) and four ringed seal samples (one
stomach only, three stomach and colon), collected by
hunters from Kivalina and Kotzebue were examined.
Two bearded seal samples and one ringed seal
sample contained prey items; the other stomachs and
colons were empty. The bearded seal stomach
samples contained mostly shrimp, bivalve mollusks,
such as clams, and crabs, as well as otoliths
from several species of fish (flatfish, Arctic cod,
sculpin, Pacific cod, prickleback). The ringed
seal sample contained fish otoliths (Arctic cod,
flatfish and sculpin) in the stomach, and shrimp and
gammarid amphipods in the colon (the amphipods may
have been present as a result of prey initially
eaten by the fish).
By John Bengtson.
Estimating Abundance of
Harbor Seals From Aerial Surveys in the Gulf of
Alaska
Harbor seals (Phoca vitulina richardsi) in
Alaska occupy a geographically extensive range from
approximately 130EW
to 172EE
(over 3,500 km east to west) and from 61EN
to 51EN
(over 1,000 km north to south). In recent
decades, the abundance of harbor seals has declined
at several Alaskan locations. For example,
counts of harbor seals at Tugidak Island declined
85% between 1976 and 1988 and counts in Prince
William Sound suggest declines in harbor seal
populations of approximately 63% between 1984 and
1997. The significance and causes of these
declines are unknown, but concern is rising about
the present and future status of harbor seal
populations, most notably in the Gulf of Alaska.
Reliable estimates of harbor seal abundance are
needed for assessing the status of populations and
for developing sound conservation and management
plans. The most feasible approach to
estimating regional harbor seal abundance is to use
aircraft to count seals when they haul out of the
water and are visible. There are many
factors, however, that affect the propensity of
seals to haul out. These factors, or ‘covariates’
include tides, weather, time of day, and date in the
seals’ annual life history cycle. Although
surveys for harbor seals have been designed to
reduce the effects of these covariates, it is not
practical to conduct a survey that would minimize
all the covariate effects simultaneously.
Therefore, it is important to adjust for the
state of the covariates during the aerial surveys.
An analysis of covariate effects on counts of harbor
seals in the Gulf of Alaska has been completed by
NMML staff. The aims of this study were to 1) gain a
better understanding of the life history processes
and environmental conditions that affect the timing
and numbers of seals hauled out during aerial
surveys, and 2) derive minimum estimates of the
abundance of harbor seals in the Gulf of Alaska.
A total of 1,366 counts of harbor seals was
obtained at 299 haul-out sites during surveys in
1996. The effects of the covariates on these
counts were estimated by a generalized additive
model (GAM) that allowed for over dispersion
relative to the usual assumption of
Poisson-distributed counts. The GAM framework
allows the data to suggest the functional shapes of
the covariate effects, which in this case were
consistent with expectations. For example, the
greatest numbers of seals were hauled out at low
tide on terrestrial sites, but tide made little
difference in the numbers hauled out on glacial ice.
The combined effects of the covariates were
substantial. The unadjusted mean count of
seals (16,355), a minimum estimate of abundance, was
only about half the magnitude of an index adjusted
to the optimal state for each covariate (31,572
seals).
One important step remains, however, in using this
index to estimate the total abundance of harbor
seals in the Gulf of Alaska. Even at the
(hypothetical) optimal conditions for all of the
covariates, some unknown fraction of the seal
population would likely remain in the water,
uncounted by surveys of the haul-out sites.
This fraction is being estimated by regression
modeling of radio-telemetry data from studies
conducted in conjunction with the aerial surveys
(AFSC Quarterly
Report July-August-September 2000).
The covariate-adjusted counts and the estimate of
the fraction of seals remaining in the water will be
combined for a final estimate of harbor seal
abundance. A major goal of the Polar
Ecosystems Program is to extend this procedure to
the other survey regions to produce a statewide
estimate of harbor seal abundance in Alaska.
By Peter Boveng.
Alaska Harbor
Seal Research Plan
Scientists and managers from the NNML Polar
Ecosystem Program, Southwest Fisheries Science
Center, ADF&G, and the NMFS Alaska Regional
Office met in Seattle (21-23 March 2001) to update
the Alaska Harbor Seal Research Plan and coordinate
joint and independent research planned for the next
year. The Research Plan was first developed in
August 2000 and will be revised annually. The plan
provides a 5-year outlook on research needed for the
sound management of harbor seals in Alaska.
The specific objectives of the plan are to 1)
consolidate overlapping studies into a coordinated
effort, 2) identify needed but unfunded research, 3)
increase communication and collaboration between
scientists and managers, and 4) ensure that the
research conducted satisfies management objectives.
The current plan covers research on abundance
and trend estimation, stock identification, habitat,
health and condition, food habits, life history,
vital rates, and human interactions.
By Dave Withrow.
Humpback Whale Research
in Japan
For the past 15 years, researchers working
throughout the North Pacific have been sending
humpback whale photo-identification data to a
centralized database managed by the NMML. In
the North Pacific, there are three different stocks
of humpback whales:
-
western North
Pacific, which winters in Japanese waters
-
central North
Pacific, which winters in Hawaiian waters
-
eastern North
Pacific, which winters in Mexican waters
Whales from all
three stocks migrate north to separate feeding areas
(mostly in U.S. coastal waters) as summer
approaches. Because humpback whales are distributed
throughout waters managed by different countries,
any large-scale collaboration on humpback whales
involves international cooperation including
researchers from Japan, the United States and
Mexico.
Sally Mizroch of the NMML was invited to present
collaborative results in a paper entitled “Vital
rates of humpback whales estimated from ocean
basin-scale collaborations” at a symposium on
humpback whales held 4 March 2001 at the Nagoya City
Science Museum, Nagoya, Japan. Results of
studies of calf mortality and adult survival were
presented, as well as the history and description of
the North Pacific database, which includes over
24,000 photographs of humpback whales taken from the
mid-1960s through the present time.
The principal humpback whale areas in Japan are the
Okinawa and Ogasawara island chains, and the primary
focus of the Nagoya symposium was the research
results of the first 10 years of humpback whale
study in Okinawa. Senzo Uchida of the Okinawa
Expo Aquarium (OEA) presented a paper outlining
cetacean research in Okinawa, and his colleague
Naoto Higashi (OEA) presented the results of their
10-year research program. Researchers working in
Okinawa have identified 331 humpback whales, and
have resighting rates year-to-year that average
about 40%.
By Sally Mizroch.
Seabird Bycatch in Alaska
Groundfish Fisheries
Seabirds are incidentally caught in various
commercial hook-and-line (longline) fisheries in the
world. In the groundfish fisheries off Alaska,
longlines account for most seabird bycatch.
Longlines may catch surface-feeding seabirds that
are attempting to feed on baited hooks. During
setting of the line, seabirds are hooked as they
attempt to capture the bait. Birds that
habitually scavenge floating material from the sea
surface are also susceptible to being hooked on
longlines.
For the past several years the NMFS Alaska Regional
Office and the AFSC have been developing a program
to address seabird bycatch issues and the associated
requirements that have resulted from the Endangered
Species Act Section 7 consultations with the U.S.
Fish and Wildlife Service on the effects of the
longline fisheries off Alaska on the endangered
short-tailed albatross. Within the scope of this
program is the calculation of annual estimates of
the numbers of birds (by species) taken in the
groundfish fisheries of the Bering Sea and Aleutian
Islands (BSAI) management area and the Gulf of
Alaska (GOA). NMML has been calculating
bycatch mortality rates of marine mammals in the
trawl, longline, and pot gear groundfish fisheries
of Alaska for more than 20 years, and databases and
analytical methodology to assess both marine mammal
and seabird bycatch are similar. Therefore,
NMML is currently cooperating with the Alaska
Regional Office and the North Pacific Groundfish
Observer Program (AFSC) to analyze the Observer
Program data to estimate annual seabird bycatch
rates and total takes since 1993.
As part of this cooperative research effort, NMML
has calculated rates and estimates by seabird
species or species group for longline, trawl, and
pot gears; statistical fishing area region (BSAI or
GOA); vessel type (processors, motherships, and
catcher-only vessels); and time periods (annual or
each of 13 four-week periods in a year) for each
year from 1993 to 2000. The data were
categorized into 11 groups of seabirds for analysis:
-
short-tailed
albatross (Phoebastria albatrus)
-
black-footed
albatross (P. nigripes)
-
Laysan albatross
(P. immutabilis)
-
unidentified
albatross
-
northern fulmar
(Fulmarus glacialis)
-
gulls
-
shearwaters
-
unidentified
tubenoses (procellarids)
-
alcids
-
other bird
species
-
unidentified
seabirds (those not identified to one of the
other ten groups).
Bycatch rates were
calculated per 1,000 hooks set for longline
fisheries, per 1,000 pots set for pot fisheries, and
per 10,000 metric tons of groundfish catch for trawl
fisheries. Estimates of total take were
calculated using the NMFS Alaska Regional Office “Blend”
total fishery effort data on the total tonnage of
groundfish catch; the total numbers of hooks or pots
set in the fishery were estimated using the numbers
of hooks or pots set on observed vessels and their
average annual values to estimate effort by
unobserved vessels of similar vessel types.
During 1993 to 1999, an average annual take of
17,000 seabirds were estimated incidentally caught
by longline fisheries off Alaska (80% of this
estimated bycatch take occurred in the BSAI
management area). Northern fulmars accounted for 60%
of this estimated bycatch. The remaining 40% of this
incidental take of seabirds by longline fisheries in
the BSAI region was comprised of gulls (17%),
albatrosses (5%), shearwaters (4%), other species
(2%), and unidentified seabirds (12%).
By Charles Fowler.
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