NMML Small Cetacean Aerial Survey 1998

National Marine Mammal Laboratory

Dataset credit

National Marine Mammal Laboratory


Primary contact Roderick Hobbs National Marine Mammal Laboratory
Data entry Kimberly Goetz Duke University



Researchers from NMML's Cetacean Assessment and Ecology Program conducted the 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.


A 3-year 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). 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.

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.

Supplemental information





Attributes described below represent those in the original dataset provided by the provider.
Only minimum required attributes are visible and downloadable online. Other attributes may be obtained upon provider's permission.

Attributes in dataset

Attribute (table column)Description
latitudeLatitude in decimal degrees
longitudeLongitude in decimal degrees
countThe number of animals
speciesSpecies code
geomGeometry field added by OBIS-SEAMAP
oidUnique ID number (generated by OBIS-SEAMAP)
Marine mammals305
Sea turtles0
Rays and sharks0
Other species0
Non spatial0
Non species0
Date, Begin1998-05-31
Date, End1998-07-27
Temporal prec.111111
Latitude56.23 - 60.84
Longitude-157.41 - -144.29
Coord. prec.4 decimal digits
Data typeAnimal sighting
EffortYES (ID: 119)
Traveled (km)10,028
Effort hours53
Contr. through
Sharing policy CC-BY-NC (Minimum)
Shared with OBIS
GBIF (via DOI)
See metadata in static HTML
See metadata in FGDC XML
See download history / statistics