2002 aerial surveys for harbor porpoise and other marine mammals off Oregon, Washington, and British Columbia

From 6 August to 12 September 2002, Cascadia Research conducted aerial surveys for harbor porpoise, Phocoena phocoena and other marine mammals under contract from the National Marine Mammal Laboratory.  The surveys were flown over the coastal waters of Oregon, 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 this first year.    

The survey area was divided into 11 strata (A-K) with each containing several modified sawtooth line-transect routes. Most (5) of the 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 Oregon, 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 111 hours were flown (not including ferry of the aircraft from Oxnard, California). Of these 42.6 hours were flown on-effort covering 4,010 nmi. A total of 86% of this (36.5 h and 3,434 nmi) were conducted in ‘good’ weather conditions. Surveys coverage was fairly complete in most of the 11 regions except northern Washington. Off northern Washington, permit conditions to avoid impacts on eagles and cormorants prevented flights early in the survey period and poor weather prevented most flights later in the survey period.  

A total of 1,696 sightings of 4,765 animals were made both on and off effort. These represented 5 baleen whale species, 4 delphinid species, 2 porpoise species, 5 pinniped species, and 2 otters. Sightings of harbor porpoise (607 sightings of 935 animals) and harbor seals (806 sightings of 2,823 animals) together accounted for 83% of the sightings. Harbor porpoise were seen in all regions (536 sightings of 836 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. 

Citation:

Chandler, T., and J. Calambokidis. 2003. 2002 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