JAS 1998 Quarterly Rpt. sidebar
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(Quarterly
Report for Jul-Aug-Sept 1998)
Small
Cetacean Aerial Survey in the Gulf of Alaska
An abundance study of harbor
porpoise (Phocoena phocoena) in Alaska was conducted by the National Marine
Mammal Laboratory (NMML) from 1991 to 1993. Aerial surveys were conducted in different
regions each year (1991: Cook Inlet and Bristol Bay; 1992: Kodiak Island and the south
side of the Alaskan Peninsula; and 1993: offshore of southeastern Alaska to Prince William
Sound). Pooling all 3 years and including a correction factor for missed animals
resulted in an abundance estimate of 29,744 porpoise. A new 3-year harbor porpoise survey
began in 1997 to complete a new abundance estimate by 1999. This survey will also
include an abundance estimate for Dalls porpoise (Phocoenoides dalli).
Researchers from NMMLs
Cetacean Assessment and Ecology Program conducted the second year of line transect aerial
surveys for harbor porpoise and Dalls porpoise from 27 May to 28 July 1998 in the
Gulf of Alaska (offshore waters from Cape Suckling to Unimak Pass), Prince William Sound,
and Shelikof Strait. Surveys were conducted from a NOAA Corps DeHavilland Twin Otter,
flown at an altitude of 152.5 m (500 ft) and an airspeed of 185 km/hr (100 knots).
Sawtooth lines were designed to cover the offshore waters from Cape Suckling to
Unimak Pass (offshore of Kodiak Island) and included lines extending 15 nmi seaward,
or to the 50 fathom line, whichever was farthest from shore and lines extending to
the 1,000 fathom line. In Shelikof Strait a series of zigzag lines were designed
between the Alaska Peninsula and Kodiak Island. Larger inlets and bays were also
included in the survey. The survey in Prince William Sound consisted of two lines:
one covering the central waters and one along the coast with extensions into selected
inlets. Two primary observers surveyed from a bubble window on the left and right
sides of the plane. An independent observer was positioned in a belly window.
This observer surveyed the trackline directly below the plane to record animals
missed on the trackline by the primary observers.
Inclement weather restricted the
completion of the entire planned survey. Survey lines were completed in Prince
William Sound and an adequate number of survey miles were completed offshore from Cape
Suckling west along the Kenai Peninsula, offshore of Kodiak Island, west to Sutwik Island
(Alaska Peninsula), and in Shelikof Strait. A total of 49.09 survey hours were
flown, with sightings of 69 harbor porpoise, 60 Dalls porpoise, 13 killer whales, 46
humpback whales, 25 fin whales, 1 Cuviers beaked whale, 11 unidentified
dolphins/porpoises, 31 unidentified whales, 21 harbor seals, 18 Steller sea lions, and 8
unidentified pinnipeds. These numbers do not include the independent bubble window
observer sightings. Once the 3 years of surveys are completed, the data will be used
to estimate annual abundance of harbor porpoise and Dalls porpoise, which is one of
the key pieces of information needed to manage marine mammal-fishery interactions, as
required under the Marine Mammal Protection Act.
By Janice Waite.
Harbor Porpoise
Tagging Research in the San Juan Islands
In mid-June NMML and NOAA Corps
personnel radio-tagged a harbor porpoise in the San Juan Islands. The 163-cm female
was the first harbor porpoise to be captured and tagged in inland Washington waters and
only the second one captured and tagged on the west coast of the United States. The
animal has been resighted and tracked 1-4 times per week over the past 4 months. The
animal has spent the majority of her time in the deep basin of the southern Straits of
Georgia and is commonly associated with other porpoises. This information will be
useful in the refinement of stock structure for west coast harbor porpoise stocks as well
as providing important habitat use information. This research is part of a project
to develop a more efficient attachment package for tracking small cetaceans.
By Brad Hanson.
Beluga Whale
Surveys in the Chukchi Sea, July 1998
In 1996 and 1997, the Alaska Beluga
Whale Committee (ABWC) supported aerial surveys to determine the distribution and
abundance of beluga whales in the Chukchi Sea. During 1996 and 1997, emphasis was on
the Kasegaluk Lagoon region, an area that had been surveyed repeatedly in previous years.
In 1998, the third and final year of the planned survey was completed. A
summary of the survey findings are currently under way. The surveys were a
cooperative effort among the ABWC, the Alaska Department of Fish and Game, and NMFS
(Alaska Fisheries Science Center and Southwest Fisheries Science Center (SWFSC)).
Douglas DeMaster, AFSC, served as the Field Project Leader. Wayne
Perryman, SWFSC, served as the lead photogrammetrist. Preliminary results of the
survey are presented herein.
Surveys were flown on 9 days during
the period 25 June through 6 July 1998. Large numbers of beluga whales were only
seen on 5 and 6 July. A single, large aggregation of whales was seen in the vicinity
of Icy Cape on both days. In addition, a relatively dispersed group of beluga whales
was seen along the ice edge.
On 5 July, the maximum count of
group size, based on four passes during which independent counts were made on each pass by
observers on the right and left side of the aircraft, was 615 animals. The estimated
school size of this same group, based on multiple counts of animals on 5 inch format
photographs, was 592 animals. On 6 July, the aggregation seen on 5 July had moved a
few miles to the north and east. The best visual count based on the maximum count
from two passes where observers were able to estimate group size was 917 animals.
The comparable count based on photogrammetric methods was 1,018 animals.
Based on analysis of the
photographic images from surveys done in 1996 and 1998 in this area, calf lengths could be
broken into three groupings: 1) 144 - 175 cm, 2) 203 - 228 cm, and 3) 240 - 278 cm.
Also, a majority of calves were accompanied by females up until a length of 230 cm.
Animals longer than 280 cm were never associated with a large adult. The
average length of animals in 1996 and 1998 was not significantly different (1996: mean
length = 359 cm, SE = 2.8 cm; 1998: mean length = 360 cm, SE = 6.8 cm). The maximum
length of animals sampled in 1996 was 402 cm, while the maximum length of animals sampled
in 1998 was 414 cm. Finally, the average length of cows accompanied by calves
was 360 cm (SE = 2.8 cm) where the smallest cow was 307 cm in length and the largest cow
was 414 cm in length.
The photogrammetric data added
considerably to the information collected during this survey. In addition, to
confirming visual estimates of group size, the length-frequency data support the
conclusion that beluga whale calves are typically weaned at two years of age.
Therefore, the most common reproductive interval is likely 3 years.
Information on the percent of calves in the population (based on length and color
data) and estimates of survival from birth to one and two years of age (based on length
data) may be possible. These analyzes are currently underway. These findings will be
compared to the information collected from the biological sampling of the annual
subsistence harvest. Finally, the data on asympotic length will be used to
supplement the current information available on stock structure.
By Douglas DeMaster.
Harbor Seal
Studies in Alaska
The Alaska Harbor Seal Task of the
NMML recently completed its summer research projects during August. Aerial
assessment surveys were conducted in the southern portion of Southeast Alaska from
Frederick Sound to the U.S.-Canadian border. Last year the northern portion of
southeast Alaska was censused. Two observers worked out of Petersburg, and five
observers used Ketchikan as their base of operations. From 18 to 28 August, the
entire coastline was surveyed from small, single-engine aircraft equipped with floats, at
an altitude of 200-250 m (700-800 ft). Observers estimated the number of seals hauled out
and took photographs of all seal haulouts. More accurate counts from the photos will
be made at NMML during the fall.
When seals are censused from the
air, an unknown number of seals are in the water and not present at the haulout sites.
A companion project to the aerial assessment surveys was to develop a correction
factor for each haulout type (rocky, sandy, and ice) to account for seals not present at
the time of the census surveys. Seals were captured and a small VHF radio
transmitter was attached to the left rear flipper. The proportion of tagged seals
hauled out was calculated during aerial census flights and from remote data-collection
computers placed nearby. The reciprocal of the observed proportion of seals hauled
out was used as the resulting correction factor.
Correction factors have been
developed earlier for seals hauling out on rocky and sandy substrates. Little is
known about the seals hauling out on glacial ice since no one has been able to
successfully capture ice-associated harbor seals. The staff of the Harbor Seal Task
has developed new capture techniques using a variety of net materials and types and net
deployment methods. In early August, 19 seals were successfully captured at Aialik
and Peterson Glaciers in the Kenai Fiords National Park near Seward, Alaska. The seals
were instrumented with VHF radio transmitters and the movements and haulout patterns
tracked from aircraft (22 August - 2 September) and remote data collection computers (19
August to about 8 October). These data will be analyzed during the fall and winter.
Two young rehabilitated harbor seals were released at Aialik Glacier by the Seward
Sea Life Center. The movements and haulout patterns of these seals were also
recorded.
Results from the assessment and
correction factor surveys will be used to estimate the number of harbor seals in Alaska
and determine key components used in the NMFS stock assessment reports.
By Dave Withrow.
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