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Wildlife Crossings on Highways


The 133-mile Sterling Highway and 38-mile Spur Highway are the only designated state highways on the western side of the Kenai Peninsula.  Less than 22 miles of this highway system actually pass through the Kenai National Wildlife Refuge, from the Russian River (MP 55) to the Sterling development corridor (MP 76), so why is the refuge so concerned about the cumulative effects of highway traffic and highway projects?    

Vehicle traffic:  In 2009, ~1.4 million vehicles traveled through the refuge, averaging 2.7 vehicles per minute.  This traffic volume exceeds (by 60%) the hypothesized threshold of 100 vehicles per hour beyond which highways become significant barriers to grizzly bear movement (Waller and Servheen 2005).  Traffic volume of this magnitude also helps translate to an average of ~225 moose killed annually over the last decade by vehicles on the Kenai Peninsula.

Peninsula-wide wildlife movement:   The Sterling and Spur Highways have the potential to segregate some wildlife species on the Kenai Peninsula into two subpopulations due to mortality by vehicles and/or avoidance of vehicles.  The total linear distance from the mouth of the Kenai River to the Seward Highway (along the eastern most edge of Kenai Lake) is 65 miles.  After eliminating Kenai Lake and Skilak Lake as natural barriers to wildlife movement, the remaining potential segment for north-south movement is 38.5 miles.  However, the continuing urbanization in the Kenai-Soldotna-Sterling area and in Cooper Landing has severely bottlenecked passage for landscape-level wildlife movement.   Only two corridors remain that allow unrestricted (except for the highway) wildlife movement between the northern and southern parts of the refuge:  a 3.5-mile wide segment immediately west of the mouth of Skilak Lake and a 4-mile wide segment from the headwaters of Skilak Lake to the west end of the MP45-60 project.  These two corridors combined represent < 20% of the historical area available for north-south movement by wildlife.  The refuge is clearly concerned about this gradual severing of the Kenai Peninsula into two distinct parts.  In our 2010 Comprehensive Conservation Plan, an 0.5-mile wide travel corridor for wildlife was established along the north shore of Skilak Lake in which no new Refuge trails, boat launches or campgrounds) will develop.   

Stream hydrology and salmon populations:  Although the headwaters of most streams on the western side of the Kenai Peninsula are within refuge boundaries, many of these streams are vulnerable because they flow under the highway system to reach the Cook Inlet.  Twelve of these streams are listed in the Anadromous Waters Catalog:  the Kenai River, Ninilchick River, Kasilof River, Moose River, Deep Creek, Crooked Creek, Slikok Creek, Soldotna Creek and Jean Creek flow under the Sterling Highway; the Swanson River, Beaver Creek and Bishop Creek flow under the Spur Highway.  In addition, the Resurrection River, which includes refuge lands within the upper reaches of its watershed, flows under the Seward Highway before reaching Resurrection Bay.  Within these 13 watersheds, there were 13 bridges and 27 culverts on the highway system in 2011; 19 of these crossings are catalogued by the Kenai Watershed Forum as providing inadequate or marginal passage for anadromous fish.

Invasive species:  Vehicles and the highway corridor are not only vectors for invasive plants onto the Kenai Peninsula, they are also significant conduits for invasives being introduced into Refuge watersheds that intersect the highway system.  Data from the Alaska Exotic Plant Information Clearinghouse in 2011 indicates that 11% of 13,896 infestations of more than 110 exotic plant species on the Kenai Peninsula are within 150m of either the Sterling or Spur Highways.  Of 706 records of reed canary grass, a highly invasive species that has the potential to compromise the integrity of stream hydrology and anadromous fisheries, 12% are along the highway system.  In fact, the Kenai Peninsula Cooperative Weed Management Area recently developed a spatially-explicit strategic plan for managing reed canary grass that is based, in part, on the nexus of highways and streams (

Noise:  Traffic sounds can both disturb wildlife and degrade the experience of visitors to Kenai Wilderness.   Vehicle noise was measured on and adjacent to the Sterling Highway in July 2004, a period of peak vehicle traffic.  Highway noise averaged 72 dB (SE = 0.26, n = 180) immediately on the highway, about the equivalent of typical construction equipment, although values as high as 120 dB were recorded for short periods. Where the Sterling Highway passes through forested areas, most vehicle-generated noise was reduced to background levels in the first 100–200 meters from the highway. However, vehicles continued to be heard above background noise levels more than 500 meters from the highway where the highway passed through open areas (primarily muskegs).

Study of wildlife movement along Milepost 58–79 of the Sterling Highway

An interagency group consisting of representatives from the Alaska Department of Fish & Game, Alaska Department of Transportation & Public Facilities, Alaska Department of Public Safety, Alaska Moose Federation, Federal Highway Administration, and the Kenai National Wildlife Refuge jointly conducted a study in 2005-2007 entitled “Wildlife Mitigation and Human Safety for Sterling Highway Milepost 5879 Project”.  The purpose of this cooperative effort was to improve human safety by reducing wildlife-vehicle collisions (WVC) along the Sterling Highway corridor through the Kenai National Wildlife Refuge while maintaining permeability and allowing wildlife to freely move across the Refuge landscape.

Female moose were tagged with GPS collars in Oct-Nov 2005 (n = 31) and 2006 (n = 32).  Female caribou was also collared in 2006 (n = 5) and 2007 (n = 7).  Of the 59 moose and 9 caribou collars retrieved, 558,239 locations were downloaded, resulting in 1,107 crossings of the Sterling Highway within the project area.  Between Nov 2005 and Jan 2009, 232 hotline phone calls from the motoring public reported 389 animals within the study area including 24 black bears, 11 brown bears, 117 caribou, 9 lynx and 230 moose.  There were also 174 WVCs documented within the study area during 2000–2007, including collisions with 24 black bear, 3 brown bear, 5 caribou and 142 moose.  The area of highest concern was between MP 69 – 75, a 6-mile section in which 48% of WVCs, 68% of wildlife hotline sightings, and 83% of GPS moose and caribou crossings occurred.  

Details of this study can be found in Wildlife Mitigationand Human Safety for Sterling Highway MP58–79 Project.  This report presents sound scientific information on moose crossings, limited caribou crossings as well as transportation infrastructure impacts on wildlife and habitat, and how to best address and minimize those impacts.

Last Updated: Mar 18, 2014
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