(Quarterly Report for Jan-Feb-Mar 2001)
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
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
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)
northern fulmar (Fulmarus glacialis)
unidentified tubenoses (procellarids)
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.