Brachyramphus marmoratus

Tree- and ground-nesting populations exhibit no morphological divergence and little genetic divergence (Pitocchelli et al. 1995).

Populations on Asian and North American sides of Beringia exhibit mtDNA differentiation consistent with species-level distinctness (Zink et al. 1995); because sample sizes were small, Zink et al. did not recommend a formal taxonomic change. However, the (Asian) long-billed murrelet (B. perdix) was subsequently split from the American B. marmoratus (Friesen et al. 1996, AOU 1997).

Friesen et al. (1996) examined variation in the mitochondrial cytochrome b gene and in 39 allozyme loci for North American and Asian (then B. m. perdix) marbled murrelets and Kittlitz's murrelet (B. brevirostris) and found significant genetic variation among marbled murrelet populations from different sites within North America.

Genetic data presented by Piatt et al. (2007) indicate that the marbled murrelet is represented by three populations, comprising birds in (1) the central and western Aleutian Islands, (2) central California, and (3) the center of the range from the eastern Aleutians to northern California.

Extensive range along the Pacific coast of North America from Alaska to California; population numbers still high in British Columbia and Alaska, but declining; threats from habitat loss due to logging, oil spills, and gill net fisheries are increasing.

Rank of G3 was confirmed using NatureServe Rank Calculator Version 3.1.

Breeding range extends from the western Aleutian Islands through coastal southern and southeastern Alaska, British Columbia (up to 100 kilometers inland), Washington, Oregon, and northern central California (mainly Del Norte and northern Humboldt counties to 15 km inland, southcentral Humboldt County 20-40 km inland, and southern San Mateo and northern Santa Cruz counties up to 20 km inland; Carter and Erickson in Carter and Morrison 1992); few occupied sites are known between Tillamook County in Oregon and the Olympic Peninsula in Washington (USFWS 1994). See USFWS (1994) and Federal Register (10 August 1995) for maps of proposed Critical Habitat in California, Oregon, and Washington. During the nonbreeding season, the range extends from southern Alaska south to central California, mostly adjacent to known or suspected nesting areas. Most of the Alaskan population is concentrated offshore of large tracts of coastal coniferous forests in southeastern Alaska (Alexander Archipelago), Prince William Sound, and the Kodiak Archipelago (Piatt and Ford 1993). See Marshall (1988), Carter and Morrison (1992), and Piatt et al. (2007) for further details for specific states and provinces.

Coded range extent pertains to breeding range.

Total number of occurrences has not been determined using standardized criteria. Determination of the number of occurrences would be necessarily arbitrary and not particularly informative with regard to the conservation status of this species.

Specific nesting and foraging areas are still being described (Simons 1980; Day et al. 1983; Marshall 1988; Carter and Sealy 1987; Quinlan and Hughes 1990; Singer et al. 1991; Ralph et al. 1995).

Most populations are dependent on large trees in old-growth forests for nest sites. Continued harvest of old-growth and mature coastal coniferous forest that reduces critical nesting habitat is a major concern throughout most of the range (Sealy and Carter 1984, Marshall 1988, Mendenhall 1992, Rodway et al. 1992, Leschner and Cummins 1992, Nelson et al. 1992, Carter and Erickson 1992, Carter and Morrison 1992; see also Rodway 1990 COSEWIC report). Marbled murrelets have lost about 15 percent of their suitable nesting habitat in Southeast Alaska, and 33 to 49 percent in British Columbia, from industrial-scale logging within the past half century (Piatt et al. 2007). Ralph (1994) estimated that 80 percent of the old-growth forests within the range of this species in the Pacific Northwest had been removed over the last 150 years.

Marbled murrelets are vulnerable to incidental mortality associated with salmon gillnet fisheries (Sealy and Carter 1984, Wynne et al. 1991). The gill-net threat is greatest north of Oregon (Levy 1993). Annual bycatch mortality in salmon gillnetting operations in British Columbia and in Alaska (especially in Prince William Sound and Southeast Alaska) is likely in the low thousands per year, although bycatch rates are difficult to measure (Piatt et al. 2007).

The species' inshore distribution coincides with high levels of vessel traffic and makes them especially vulnerable to both chronic oil pollution and to catastrophic spills (King and Sanger 1979, King 1984, Sealy and Carter 1984, Mendenhall 1992, Rodway et al. 1992, Leschner and Cummins 1992, Nelson et al. 1992, Carter and Erickson 1992, Piatt et al. 2007). The 1989 Exxon Valdez oil spill in south-central Alaska is estimated to have killed 12,000 to 15,000 murrelets (Piatt et al 2007).

Other threats include direct and indirect mortality associated with the location and operation of mariculture facilities. These threats include: entanglement, displacement of birds from traditional foraging areas, contamination of foods by antibiotics, antifoulants, and alteration of local food supplies due to decomposition of fish food and fish excrement associated with these farms (Vermeer and Morgan 1989, Rodway et al. 1992, Leschner and Cummins 1992). Murrelets in some areas may also be subject to high levels of industrial pollutants (Fimreite et al. 1971, Rodway et al. 1992).

Listed populations are currently experiencing very low recruitment rates, due at least in part to nest predation (by edge species, such as bald eagle, common raven, and Steller's jay, that are now more abundant due to forest fragmentation) and probably high mortality in young prior to reaching the ocean (USFWS 1994, 1996). Populations in the Aleutians may have been higher before foxes were introduced there (Mendenhall in Carter and Morrison 1992).

Finally, nesting habitat losses cannot explain the declines observed in areas where industrial logging has not occurred on a large scale (e.g., Prince William Sound) or at all (Glacier Bay) (Piatt et al. 2007). Those declines probably are related to combined and cumulative effects from climate-related changes in the marine ecosystem (most likely the 1977 regime shift) and human activities (logging, gillnet bycatch, oil pollution) (Piatt et al. 2007).