Speich and Wahl 



Chapter 30 



Marine Habitat Preferences, Variability in Washington 



time period. Densities were calculated by dividing the total 

 numbers of Marbled Murrelets observed by the total area 

 censused on all censuses within each habitat types for the 

 specific time period. Data from 1978 and 1979 were combined. 



Surveys similar to the MESA bird program, partially 

 funded by NOAA and the Washington Department of Wildlife, 

 were later established for southern Puget Sound (Wahl and 

 Speich 1983, 1984). These surveys were designed to allow 

 the quantification and appraisal of the general, seasonal 

 distribution and abundance of all marine waterbird species 

 in southern Puget Sound. This program consisted of one 

 complete summer survey of the area and extensive winter 

 surveys (as yet unpublished) over several years. All winter 

 surveys were from light aircraft and summer surveys were 

 from small boats and light aircraft following the methods set 

 forth in Wahl and others (1981, see above). Results are 

 expressed as birds per square kilometer and are summarized 

 by geographic area, inshore or offshore, and time period. 



There are only limited data from the Pacific Ocean coast 

 of Washington that quantify the occurrence of Marbled 

 Murrelets in marine habitats. The best data are for the southern 

 outer coast, the coast south of Point Grenville, including the 

 Grays Harbor Channel and habitats in the shelf waters off the 

 mouth of Grays Harbor channel to the continental shelf break 

 (Wahl 1984), and the onshore area in the vicinity of Point 

 Grenville (Speich and others 1987, 1992). Along the north 

 portion of the coast, the area north of Point Grenville, only 

 limited data are available for the nearshore and offshore 

 waters of the continental shelf (Speich and others 1992). 

 Censuses of birds over the continental shelf, to the shelf 

 break, off of Grays Harbor, were made from chartered fishing 

 boats, from 1971 to the present. Census frequency, especially 

 during the winter storm period, was often limited for access 

 to the ocean due to rough bar and sea conditions. All birds 

 observed were counted and summarized for transects of varying 

 length within specific water depth intervals, and results are 

 expressed as birds observed per linear kilometer, as described 

 in specific detail by Wahl (1984). Observations of birds of 

 specified nearshore water areas from three land locations 

 near Point Grenville were accomplished with the aid of 

 binoculars and telescopes during the spring-summer periods 

 of 1984 and 1985 (Speich and others 1987). Observations 

 were expressed as Marbled Murrelets observed per square 

 kilometer for consecutive week periods. North of the Point 

 Grenville study area, observations were made from boats 

 (Zodiacs) while moving up and down the coast over nearshore 

 waters of the continental shelf (Speich and others 1992). All 

 birds observed in moving zones about the vessel were recorded, 

 with results expressed as birds per square kilometer. 



Results 



Abundance and Occurrence by Habitat Types - 

 Puget Sound 



For northern Puget Sound, the seasonal densities and 

 percent occurrence of Marbled Murrelets were determined 



for censuses within five broad habitat groups, each in turn 

 subdivided into several more specific habitat types (table 1, 

 figs. 1-10). 



Open Water Greater than 20 m Depth 



In Sequim and Discovery bays, the large sheltered bays 

 at the eastern end of the Strait of Juan de Fuca, Marbled 

 Murrelets reach peak abundance during the fall period (table 

 l,fig. 1). No other habitat within this habitat group had as 

 high a density, 2.5 birds/km 2 . The maximum density obtained 

 during the winter period, 0.92 birds/km 2 , was also from 

 Sequim and Discovery bays. Concentrations of Marbled 

 Murrelets were also reported from this area on Audubon 

 Christmas Counts, according to summary statements by Speich 

 and others (1992). 



Within this habitat group, the proportion of individual 

 censuses with Marbled Murrelets was generally near, and 

 often less than, 20 percent (0.2) (table l,fig. 2). The exception 

 was the summer period for Sequim and Discovery bays 

 where Marbled Murrelets were observed on 50 percent of all 

 censuses in the area, but the sample size (n = 2) is very 

 small. Within this habitat group, the deep open waters within 

 the San Juan Islands showed peak numbers (density) and 

 occurrence rate during the summer and fall periods (table 1, 

 figs. 1 and 2). 



Bays with Steep and Gradual Slopes 



Habitat types within the group, "bays steep and gradual 

 slopes", are described by location and type (table l,figs. 3 

 and 4). These habitat types generally are characterized by 

 low densities of Marbled Murrelets. High densities of four 

 and five murrelets per square kilometer, were found in habitats 

 on steep slope and sand substrate within Whatcom and Skagit 

 counties (Chuckanut Bay) and within the San Juan Islands, 

 during the winter period. 



Although the densities of Marbled Murrelets in the habitat 

 types of this group are low, the rate of occurrence of censuses 

 with birds is nonetheless relative high. While the density of 

 birds was relatively high during the winter in steep slope 

 habitats with sand substrate within the San Juan Islands, 

 birds were only observed on about half of censuses (table 1, 

 fig. 4). This suggests that relatively large numbers of birds 

 were present during the winter in this habitat type, but birds 

 move about and were not always encountered on censuses. 

 A similar pattern was observed in this habitat type in Whatcom 

 and Skagit Counties, except in winter when birds were detected 

 on a greater portion of censuses, about 80 percent. Similarly, 

 during the spring period, birds were detected on about 90 

 percent of censuses, even though average density ( 1 .42 birds/ 

 km 2 ) (table 1) was lower than the winter period density 

 (3.92 birds/km 2 ). 



Areas of Tidal Activity 



The occurrence of Marbled Murrelets in areas of tidal 

 mixing is not unexpected, as these are generally thought of as 

 productive areas where prey concentrate in nutrient and food- 



314 



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



