Use of Boat-Based Surveys to Determine Coastal Inland Habitat Associations of Marbled Murrelets in Prince William Sound, Alaska

Abstract

Listen

Translate article

To identify potential marbled murrelet (Brachyramphus marmoratus) nesting habitat we surveyed western Prince William Sound, Alaska, for murrelet activity between 12 June and 3 August 1992. We evaluated methods specific to boat-based surveys (vessel and shoreline) by comparing the number of murrelet detections and subcanopy flights during dawn watches adjacent to inland stations. We conducted boat-based surveys from a l9-m vessel (N = 44) and from shoreline stations (N = 23), and concurrently from adjacent inland stations (N = 17). Murrelet activity level and seasonal variation of activity were not significantly different when conducted from the vessel or from shoreline and were similar to surveys at adjacent inland stations. Survey stations near bay heads had higher activity levels than those near exposed coastlines, with the exception of bays that were glaciated or recently deglaciated. We used a timber-type database on a geographic information system to analyze relationships between murrelet activity and habitat within a l-km radius of each survey station. Forested habitat, particularly forests with trees > 28 cm diameter, showed the strongest correlation to murrelet activity. Boat-based surveys are useful for a preliminary identification of potential murrelet nesting areas in remote and otherwise inaccessible, coastal habitat. In North America, most marbled murrelets (Brachyramphus marmoratus) breed in Alaska (Mendenhall 1992), and within this state, Prince William Sound (PWS) is 1 of 3 major population centers (Piatt and Ford 1993). The PWS population of murrelets was affected in the 1989 Exxon Valdez oil spill by direct mortality and possibly by disruption of breeding (Piatt et al. 1990; Ecological Consulting, Inc. 1991; Kuletz, in press). Part of the restoration effort included the identification of marbled murrelet nesting habitat throughout the affected area. During the breeding season most of the murrelet population is found offshore of old-growth forests (Piatt and Ford 1993), and many studies have shown that mature and old-growth forest constitute the primary habitat for nesting marbled murrelets south of Alaska (Paton and Ralph 1990, Rodway et al. 1993, Hamer and Nelson 1995a, Ralph et al. 1995a). In southcentral Alaska, murrelet nesting habitat includes both forested and nonforested areas (Simons 1980, Day et al. 1983, Kuletz et al. 1995). Search techniques based on observing murrelet behavior or signs of nesting (Singer et al. 1991, Nelson and Hamer 1992, Naslund 1993, Naslund et al. 1995, Nelson and Peck 1995) and radiotelemetry (Quinlan and Hughes 1992) have been used to locate small numbers of murrelet nests. Unlike many seabirds, marbled murrelets are thought to nest at relatively low densities (Carter and Sealy 1986, Naslund et al. 1995). This, combined with their concealing plumage and secretive behavior, make nests difficult to locate. Because of the difficulty in finding nests, many efforts to define habitat use have focused on surveying marbled murrelets when they fly to inland nesting areas around dawn (e.g., Paton et al. 1990). Large-scale surveys of murrelet activity at inland sites outside of Alaska are facilitated by road and trail systems that provide access to potential nesting habitat. In contrast, much of Alaska is difficult to traverse, and most coastal areas are remote and accessible only by boat or aircraft. Searches from the ground for murrelet nests are too labor-intensive to use over large areas. Before this study, methods for surveying and mapping murrelet nesting habitat over a large and remote geographic area had not been developed for Alaska. We tested new boatbased methods to survey sunrise activity of