Chapter 31 



Abundance and Distribution of Marbled Murrelets in Oregon 

 and Washington Based on Aerial Surveys 



Daniel H. Varoujean II Wendy A. Williams 1 



Abstract: To determine the abundance and distribution of Marbled 

 Murrelets, aerial surveys of the Oregon coast, Washington outer 

 coast, and shores of the western Strait of Juan de Fuca were con- 

 ducted in August/September 1993. Based on these marine surveys, 

 abundance estimates are established for Oregon (6,400-6,800 birds) 

 and the waters surveyed in Washington (3,400-3,600 birds). A 

 comparison of these estimates to those established by other surveys 

 indicates that boat-based surveys may give higher estimates of 

 murrelet abundance, and that population size has probably not 

 decidedly changed over the last 10 years in either Oregon or Wash- 

 ington. On the Pacific Ocean coast of both states, murrelets were 

 found to be unevenly distributed with birds being most abundant in 

 central Oregon and northern Washington, and present in lower 

 abundance in southern Oregon and from northern Oregon through 

 southern and central Washington. This distribution appears to be 

 related to shore type, and proximity to the entrances to major river 

 mouths and embayments, at least in Oregon, and to available inland 

 nesting habitat in both states. The ratio of hatch-year birds to the 

 total number of murrelets seen during the surveys was estimated to 

 be 5 percent. As a measure of production, this estimate is too low for 

 population maintenance, but we conclude that murrelets in Oregon 

 and Washington may not be in a long-term population decline. 



Determination of abundance and distribution is an 

 important element in the conservation management of the 

 Marbled Murrelet (Brochyromphus marmorotus). Because 

 of the secretive habits of murrelets frequenting inland areas, 

 marine surveys are the most effective means for documenting 

 population size. Only recently have systematic marine surveys 

 for murrelets been conducted over the entire length of the 

 Oregon coast, and no such sur 'eys have been conducted 

 over the extent of the Washington outer coast. Consequently, 

 even though the opportunity to do so arose late in the nesting 

 season, we carried out aerial surveys of the Oregon and 

 Washington coasts during late August and early September 

 1993. This chapter reviews the results of these surveys, 

 which are examined in more detail in two unpublished reports 

 (Varoujean and Williams 1994a, b). In addition, we compare 

 our findings to those of boat-based surveys conducted in 

 both Oregon and Washington. 



Methods 



Survey Schedule 



Various segments of the Oregon study area, which 

 extended from Pt. Saint George/Crescent City, California, 

 north to Tillamook Head. Oregon, were surveyed over the 



1 Executive Director and Research Associate, Marzet, Marine and 

 Estuarine Research Co., 2269 Broadway St., North Bend. OR 97459 



period 22-23 August 1993. Because of poor weather conditions 

 and restricted visibility, only a small portion of the south- 

 central Oregon coast was surveyed on 22 August 1993. The 

 remainder of the south coast, and all of the coast north of 

 Coos Bay were surveyed on 23 August. From the airport at 

 Grays Harbor, various segments of the Washington study 

 area, which extended from Tillamook Head, Oregon, north to 

 Cape Flattery, Washington, were surveyed over the period 4- 

 5 September. Because of a low cloud ceiling from Cape 

 Elizabeth north, only the southern two-thirds of the outer 

 Washington coast was surveyed on 4 September 1993. On 5 

 September the survey of the southern two-thirds of the outer 

 Washington coast was completed, as was the survey of the 

 coast from Cape Elizabeth north to Cape Flattery. Portions of 

 the western Strait of Juan de Fuca extending from Neah Bay 

 east to Port Angeles (on the Washington side), and from Port 

 San Juan, east to Becher Bay (on the British Columbia side), 

 were surveyed on 6 September. In general, survey viewing 

 conditions in both Oregon and Washington were good to 

 excellent with sea states of Beaufort 3 (occasional white 

 caps) or less, and long, ocean swell heights of 1 m or less. 



Survey Methods 



In both studies the survey platform was a Partenavia. a 

 high-wing, twin engine aircraft, that was flown at a ground 

 speed of 145 km/h (90 mph), and at an altitude of 60 m (200 

 ft) above sea level. Position data were recorded from an 

 onboard Loran-C instrument, to the nearest 0.1' of latitude 

 and longitude by an investigator stationed in the co-pilot's 

 seat Position data were recorded approximately every minute 

 of time to the nearest second. The data recorder's watch 

 was synchronized to the nearest second with the watches 

 used by the two observers. The two observers, one located 

 on each side of the aircraft, recorded on audio tapes all 

 seabirds and marine mammals seen on their respective 

 survey transects. Additionally, observers recorded 

 information pertaining to sea conditions, cloud cover and 

 the amount of surface glare in their field of view. Each 

 observer's transect was 50 m wide (i.e., the survey transect 

 is 100 m wide when both observers are surveying) as 

 established with a clinometer that was rotated up 50 from a 

 line extending at an angle of 5 from the lower edge of the 

 observation window to the surface of the water. Even though 

 the observers were looking approximately straight down 

 out of their respective windows, at times the surface glare 

 from sunlight off the water would hamper or preclude 

 surveying off one side of the aircraft. The analysis of 

 sighting data, any time an observer noted that >20 percent 

 of their field was obscured by glare, was limited to 



USDA Forest Service Gen. Tech. Rep. PSW-152. 1995. 



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