2003 aerial surveys for harbor porpoise and other marine mammals off Oregon, Washington, and British Columbia
Chandler, T., and J. Calambokidis. 2003. 2003 aerial surveys for harbor porpoise and other marine mammals off Oregon, Washington, and British Columbia. Contract report to National Marine Mammal Laboratory, Seattle, WA. 25pp
From 1 - 31 August 2003, Cascadia Research conducted aerial surveys for harbor porpoise, Phocoena phocoena, and other marine mammals under contract from the National Marine Mammal Laboratory. This was the second year that surveys were flown over the coastal waters of Washington and southern British Columbia and the inland waters of Washington (except Puget Sound) and southern British Columbia as part of a multi-year abundance estimate effort. This report summarizes the effort undertaken and sighting results of the second year.
The survey design was identical to the first year but included a smaller set of survey strata that did not include the Oregon and southern Washington outer coasts. As opposed to 11 regions or strata (A-K) as in 2002, there were 6 regions flown this year (F-K) with each containing several modified sawtooth line-transect routes. Two of the three coastal strata were further divided into inshore and offshore components with the offshore tracklines fewer in number. A high-wing twin-engine aircraft fitted with side bubble windows and a belly window was used with three experienced observers and a dedicated data recorder. A Data Acquisition System (DAS) interfaced with a GPS was used to streamline the data recording/entry process. Flights were conducted primarily on days with ‘good’ conditions (Beaufort sea state of 0-2, and cloud cover 50% or less). Sections flown in conditions worse than this were re-flown if possible.
The primary objectives of this study were to:
1) conduct line-transect aerial surveys off Washington and British Columbia to obtain data to estimate abundance of harbor porpoise.
2) obtain data on other species of marine mammals in these areas.
3) conduct aerial surveys in the eastern Strait of Juan de Fuca and the San Juan Islands concurrently with small boat transects in the same area.
A total of 74.5 hours were flown in the study area including transits to and from the various regions. Of these hours, 28.2 were flown on-effort covering 2,717 nmi. A total of 80% of this (22.5 h and 2,169 nmi) were conducted in ‘good’ weather conditions. Survey coverage was fairly complete in most of the six regions except northern Washington. Although heavily targeted this year due to missed effort last year, the northern Washington outer coast again proved hard to cover mostly due to fog and cloud cover but also high winds.
A total of 1,664 sightings of 4,166 animals were made both on and off effort. These represented 3 baleen whale species, 2 delphinid species, 2 porpoise species, 5 pinniped species, and 1 fissiped species. Sightings of harbor porpoise (499 sightings of 847 animals) and harbor seals (1048 sightings of 2,994 animals) together accounted for 92% of the sightings. Harbor porpoise were seen in all regions (422 sightings of 716 animals on-effort in ‘good’ weather). High concentrations of harbor porpoise were seen in the central Strait of Juan de Fuca (in conjunction with vessel surveys) and also in the northern San Juan Islands. Relatively low numbers of sightings were made in central and northern Strait of Georgia.