Salmon escapement estimates at the Little Waterfall barrier bypass, Afognak Island, Alaska: 1995 - 1998

Surveys were conducted in 1992-93 at Little Waterfall Creek (LWC), Afognak Island, to evaluate instream habitat and potential stock restoration techniques for wild salmon stocks. Data indicated that LWC contained significant amounts of spawning habitat that were underutilized by pink and coho salmon due to an ineffective barrier bypass structure. The project priorities were to renovate the bypass to reduce gradients and design resting pools to minimize water velocity. The bypass renovation was completed in the fall 1995; bypass gradients were reduced from 27% to 17-20% and two additional resting pools and an entrance pool were installed. The steeppass sections were staggered between pools to reduce the velocity of stream flows. The historical performance of the three bypasses at LWC, since installation in 1981, has been significant, increasing average pink salmon escapements from -7,000 to -70,000 fish. The number of pink salmon migrating by way of all three bypasses to spawn in upstream habitat has significantly increased resultant returns; however, regression analysis was driven by the large upstream escapement in 1993. The historical proportion of the total annual pink salmon escapement to migrate upstream has primarily been a function of the design and performance of the largest (most upstream) bypass. Publications: Honnold, S.G. 2001. Little Waterfall Creek barrier bypass improvement: Pink and coho salmon habitat enhancement, Exxon Valdez Oil Spill Restoration Project Final Report (Restoration Project 97139Al), Alaska Department of Fish and Game, Division of Commercial Fisheries, Kodiak, Alaska.1992—1993年，研究人员于阿福格纳克岛的小瀑布溪（Little Waterfall Creek, LWC）开展调查，以评估野生鲑鱼种群的河道栖息地状况及可行的种群修复技术。数据显示，LWC拥有大量未被粉鲑（pink salmon）和银鲑（coho salmon）充分利用的产卵栖息地，症结在于现有拦障旁路设施效能不足。项目优先任务为改造该旁路设施以降低坡度，并设计休憩池以最小化水流流速。1995年秋季，旁路设施改造工程完工：原坡度从27%降至17%—20%，并新增两处休憩池与一处入口池。同时，在各休憩池之间错落布设陡坡过流段，以削弱河道水流流速。自1981年三处旁路设施投用以来，LWC的历史成效显著：粉鲑的平均产卵洄游量从约7000尾提升至约70000尾。经由三处旁路设施向上游河道洄游产卵的粉鲑数量显著增加，进而提升了最终回捕量；不过回归分析（regression analysis）的结果受1993年上游大规模产卵洄游事件的影响较大。历年粉鲑总产卵洄游量中向上游迁移的占比，主要取决于规模最大（位置最靠上游）的旁路设施的设计与运行效果。参考文献：Honnold, S.G. 2001. 《小瀑布溪拦障旁路设施改造：粉鲑与银鲑栖息地改善》，埃克森·瓦尔迪兹号溢油事故修复项目最终报告（修复项目编号97139Al），阿拉斯加州鱼类与狩猎部商业渔业分部，科迪亚克，阿拉斯加。