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National Marine Mammal Laboratory

(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 Dall’s porpoise (Phocoenoides dalli).

Researchers from NMML’s Cetacean Assessment and Ecology Program conducted the second year of line transect aerial surveys for harbor porpoise and Dall’s 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 Dall’s porpoise, 13 killer whales, 46 humpback whales, 25 fin whales, 1 Cuvier’s 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 Dall’s 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.