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.

阿拉斯加州鱼类与野生动物部（Alaska Department of Fish and Game, ADFG）维护着一套鱼类通行状况清单数据库（http://www.adfg.alaska.gov/index.cfm?adfg=fishpassage.database），该数据库收录了ADFG鱼类通行评估计划中收集的溪流穿越设施鱼类通行相关数据。本计划的职责为评估州属道路跨溪流设施对鱼类通行的影响。维持洄游性鱼类（例如鲑鱼）上下溪流栖息地的通行无阻，是维系该类鱼类种群稳定的关键环节。

若设计合理，溪流穿越处的涵洞与桥梁不会对鱼类通行造成阻碍，但尺寸过小、坡度过陡或安装位置不当的涵洞，则会阻碍鱼类的上下游移动。ADFG鱼类通行评估计划会对涵洞开展快速（Level 1）评估，以判断其是否适配鱼类通行需求。溪流被划分为三类：大概率适配鱼类通行、可能不适配鱼类通行，以及大概率不适配鱼类通行。

本次评估选用的基准鱼类为体长55毫米的幼年银大麻哈鱼（coho salmon）。选择该鱼种的原因在于，研究认为幼年鲑科鱼类中银大麻哈鱼的游泳能力最弱，因此但凡能让基准鱼类顺利通行的涵洞，理论上也可满足其他所有鱼类的通行需求。

如需了解Level 1级评估的更多细节，请参阅Eisenman, M.与G. O’Doherty于2014年发布的《阿拉斯加州鱼类通行涵洞清查与评估手册：2009-2014年溪流穿越设施清查与评估操作指南》，该文档为阿拉斯加州鱼类与野生动物部特别出版物第14-08号，安克雷奇，可通过http://www.adfg.alaska.gov/FedAidPDFs/SP14-08.pdf获取全文。

本数据集基于原始ADFG鱼类通行清单数据库（http://www.adfg.alaska.gov/index.cfm?adfg=fishpassage.database）中的2500条涵洞评估记录，按照涵洞所在区域进行分类，并按类别与区域汇总了涵洞总数量。本次采用的区域划分来自阿拉斯加州“鲑鱼与人类项目”（Salmon and People Project, SASAP）的分区体系，该分区与ADFG的管理区域存在显著差异。

使用本数据集时，需充分考虑抽样效应的影响。该鱼类通行清单数据库仅收录了已完成勘测的跨溪流设施，并未覆盖全州所有涵洞。此外，由于部分区域需要重新勘测以更新自初始勘测后已更换的涵洞信息，本数据集可能无法完全准确反映当前的鱼类通行状况。部分涵洞评估数据可能存在过时问题，因为涵洞始终处于持续更换与升级的状态。最后，在解读本数据集时，必须结合基准鱼类的设定进行分析：绝大多数被判定为“不适配鱼类通行”的涵洞并非鱼类通行的完全障碍，但它们会阻碍基准鱼类——即55毫米幼年银大麻哈鱼——的通行。