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Ecoregion Description


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101: Alaskan Coastal

Major Habitat Type:

polar freshwaters

Author:

Mary Burridge and Nicholas Mandrak

Countries:

Canada; United States

Boundaries:

This region encompasses the Lower Yukon River drainage below the confluence with the Tanana River. It extends up to, but does not include the Lower Mackenzie River in the east. It is bounded by, the Beaufort Sea in the north, the Bering Sea in the west, and the Gulf of Alaska in the south. The ecoregion includes the Aleutian Islands and Bristol Bay drainages.

Drainages flowing into:

All drainages in this ecoregion flow into the Bering, Chukchi or Beaufort seas.

Main rivers or other water bodies:

The Yukon River (3200 km) is the tenth longest river in the world and the fourth longest in North America. The Lower Yukon travels from central Alaska towards the Bering Sea. Koyukuk River is a major tributary of the Lower Yukon. Other river drainages in the ecoregion include the Colville, Noatak, Kobuk and Kuskowkwim.

Topography:

This ecoregion ranges from flat coastal plains to the rugged, deeply dissected mountains of the Brooks and Alaska ranges. Much of the area is level to gently rolling with many lakes and rivers. In the Alaskan interior, broad valleys and basins are typical, along with some rolling hills and piedmont slopes. Elevations within the ecoregion range from sea level to over 2500 m (McNab & Avers 1994).

Climate:

Climate ranges from maritime along the coast to continental in inland areas. Average annual precipitation ranges from 100 along the northern coast to over 1500 mm along the Alaska Peninsula. Average annual temperature ranges from -13 to 4 oC across the ecoregion. Freezing temperatures may occur in any month (McNab & Avers 1994).

Much of this ecoregion was glaciated during the Wisconsin Ice Age. By contrast, the northern part of Alaska, known as Beringia, remained unglaciated and thus became one of six North American refugia during this period (Mecklenburg et al. 2002). 

Freshwater habitats:

The ecoregion includes meandering streams and side sloughs, as well as oxbow, thaw, and morainal lakes. Along the coast wetland vegetation is common, including fens, bogs, and marshes (McNab & Avers 1995). The primary types of rivers include those with headwaters in the arctic region and those with headwaters further south (Mecklenburg et al. 2002). Peak flow in Arctic rivers occurs in spring and autumn, and is influenced by rain, as well as melting snow and ice. These rivers remain cool throughout the short summer, and freeze during winter, unless they are fed by perennial springs. Rivers south of the Arctic region have maximum flows between May and June, and may or may not freeze during winter, depending on their location and size. Most lakes are of glacial origin.

Terrestrial Habitats:

The ecoregion is characterized by tundra along the coast and taiga within the interior. Tundra vegetation consists of mesic graminoid herbaceous communities dominated by sedges (Eriophorum spp. and Carex spp.) and low scrub communities. Protected, well-drained valley bottoms may contain coniferous forests dominated by white spruce (Picea glauca) and balsam poplar (Populus balsamifera), or mixed forests characterized by white spruce and paper birch (Betula papyrifera). Black spruce (Picea mariana) occurs in bottomlands and other wet areas with poorly drained soils (Ricketts et al. 1999).  

Fish Fauna:

Given its northern location, this fish fauna is depauparate relative to the faunas further south, and is dominated by secondary freshwater fishes such as the Pacific salmons (Oncorhynchus spp.), chars (Salvelinus spp.) and whitefishes (Coregonus, Prosopium spp.).

A striking feature of Alaskan biogeography is the circumscribed distribution of the Alaskan blackfish (Dallia pectoralis). The world range of this strictly freshwater genus is confined to three islands in the Bering Sea and to drainages bordering the opposite shores of the Bering Sea in Siberia (Chukotsk Peninsula and Amguema River) and in Alaska (in a band of drainages stretching from Bristol Bay northward to Colville River on the Arctic Coast). Dallia survives only on parts of the Bering land bridge that escaped both glaciation and inundation during the Wisconsin Ice Age. Within the Alaskan range of Dallia there are also other fish species displaying symptoms of divergence during long isolation. The Bristol Bay area is the only place known to harbor lakes containing two (or three) sympatric forms of the pygmy whitefish (Prosopium coulterii). According to McCart (1970), it is possible to distinguish at least two forms of pygmy whitefish in samples from three Alaskan lakes: Aleknagik, Naknek, and Chignik, using meristic and morphological data. In the first two lakes distinct high and low gillraker forms are distinguishable. In Chignik there is, in addition, a third type, closest to the low gillraker form, but tending toward the high gillraker form in some characters. An analysis of geographic variation in certain meristic characters suggests a western refugium south of the ice sheet for the Alaskan low gillraker form, a Yukon-Bering Sea refugium for the Alaskan high gillraker form, and a Mississippian refugium for the Lake Superior form. Dwarf forms of the least cisco (Coregonus sardinella) with unusually high gillraker counts occur in lakes Naknek and Iliamna. On the north slope of the Brooks Range there are peculiar populations of grayling (Thymallus arcticus articus), and, in springs and headwaters, morphologically distinct populations of Arctic char (Salvelinus alpinus). In all there are at least seven fish species within this unglaciated refugium that show evidence of endemic variation (Lindsey and McPhail 1986; C. Lindsey, pers. comm.).

Description of endemic fishes:

The only known endemic species is the Angayukaksurak char (Salvelinus anaktuvukensis), restricted to streams on the crest of the Brooks Range.

Ecological phenomena:

Many species in this ecoregion exhibit anadromy, including Pacific salmons (Oncorhynchus spp.), chars (Salvelinus spp.) and whitefishes (Coregonus spp.). The Yukon is one of the most important salmon-breeding rivers in the world. Chinook salmon (Oncorhynchus tshawytscha) migrate more than 2,000 km from the Bering Sea, returning to spawn in tributary creeks (Mecklenburg et al. 2002).

Justification for delineation:

This ecoregion includes a tier of river systems along the western and northern coasts of Alaska, including the drainages of Bristol Bay, the lower Yukon River, and the coastal drainages up to the watershed divide at the MacKenzie River delta on the Arctic slope. The region incorporates most of the unglaciated areas from the Wisconsin Ice Age that contain relict species, most prominently the Alaskan blackfish (Dallia pectoralis). The Lower Yukon River is separated from Upper Yukon because of a high dissimilarity between their fish faunas and the history of the Lower Yukon as a glacial refuge zone (Lindsey and McPhail 1986). The dividing line between the Lower and Upper Yukon coincides with the farthest upstream records of Dallia at Tanana and Fairbanks (C. Lindsey, pers. comm.).

Level of taxonomic exploration:

Fair / Poor

References/sources:

Abell, R., Olson, D., et al. (2000). "Freshwater ecoregions of North America" Washington, D.C.: Island Press.

Eswg (1995) "A national ecological framework for Canada". Ottawa/Hull, Ontario, Canada. Agriculture and Agri-food Canada, Research Branch, Centre for Land and Biological Resources Research; and Environment Canada, State of the Environment Directorate, Ecozone Analysis Branch..

Lindsey, C. C.,McPhail, J. D. (1986)"Zoogeography of fishes of the Yukon and Mackenzie basins" In C.H, H.;Wiley, E.O. (Ed.). Zoogeography of the freshwater fishes of North America. (pp. 639–674) New York, NY USA: Wiley Interscience.

McNab, W. H.,Avers, P. E. (1994) "Ecological subregions of the United States". U.S. Forest Service, ECOMAP Team, WO-WSA-5. Online. http://www.fs.fed.us/land/pubs/ecoregions/index.html..

McPhail, J. D. and C. C. Lindsey (1970). "Freshwater fishes of northwestern Canada and Alaska" Fisheries Research Board of Canada Bulletin 173 381.

McPhail, J. D. and R. Carveth (1992) "A foundation for conservation: the nature and origin of the freshwater fish fauna of British Columbia". Field Museum, Department of Zoology, University of British Columbia..

Ricketts, Taylor H. Dinerstein Eric Olson David M. Loucks Colby J. (1999). "Terrestrial ecoregions of North America: A conservation assessment" Washington, D.C.: World Wildlife Fund.

Rowe, J. S. (1972) "Forest Regions of Canada". Ottawa. Canadian Forest Service, Department of Environment..

Scott, W. B.,Crossman, E. J. (1998). "Freshwater fishes of Canada" Fisheries Research Board of Canada Bulletin 184 966 + xvii..

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