Regional fish passage assessment, Alaska, 2000-2017

The Alaska Department of Fish and Game (ADFG) maintains a fish passage inventory database (http://www.adfg.alaska.gov/index.cfm?adfg=fishpassage.database), containing data on stream crossings for fish passage collected as part of the ADFG Fish Passage Assessment Program. This program is charged with assessing the impact of state-owned road crossings of streams on fish passage. Maintaining unobstructed access to stream habitat for fish that migrate up and down these streams (such as salmon) is a critical part of maintaining these fish populations. When designed properly, culverts and bridges at stream crossings do not present a problem to fish passage, however culverts that are too small, too steep, or placed improperly can impede both upstream and downstream movement of fish. The ADFG Fish Passage Assessment Program conducts rapid (Level 1) assessments of culverts to determine their adequacy for fish passage. Streams are classified into three categories: likely to be adequate for fish passage, may be inadequate for fish passage, and likely inadequate for fish passage. The model fish chosen to determine adequacy for passage is a 55mm (juvenile) coho salmon. This fish is chosen because coho salmon are believed to be the weakest swimmers amongst juvenile salmonids, thus any culvert passable by the model fish should be passable for all other fish. For more information on Level 1 assessments, please see Eisenman, M., and G. O’Doherty. 2014. Culvert inventory and assessment manual for fish passage in the State of Alaska: A guide to the procedures and techniques used to inventory and assess stream crossings 2009-2014. Alaska Department of Fish and Game, Special Publication No. 14-08, Anchorage. http://www.adfg.alaska.gov/FedAidPDFs/SP14-08.pdf. In this dataset, the 2,500 culvert assessments in the original ADFG fish passage inventory database (http://www.adfg.alaska.gov/index.cfm?adfg=fishpassage.database) were classified according to what region the culvert is located in. The total number of culverts by category and region were summarized. The regions used are the regions of the State of Alaska's Salmon and People Project (SASAP), which notably are different than the ADFG management areas. When using this data, sampling effects must be taken into effect. The fish passage inventory database does not include all culverts in the state, just those where surveys have been completed. Additionally, this may not be an entirely accurate picture of fish passage given the fact that many areas need re-survey to update culverts that have been replaced since the initial survey. Thus some of the culvert assessment data may be out of date, as culverts are continually being replaced and improved. Finally, the model fish must be taken into account when interpreting these data. The majority of the "inadequate for fish passage" culverts are not total barriers to fish passage, however they are barriers to the model fish, which is the 55mm coho salmon.