Decreasing river flows and increasing water temperatures during the summer have been associated with holding behavior by pre-spawning Pacific lamprey Entosphenus tridentatus in the mainstem Willamette River (Oregon, USA). However, it is unclear if microhabitat use (≤ 2 m) by these lamprey is associated with particular habitat structure(s) or thermal refuge. We implanted radio tags into lamprey (n = 425) and conducted boat surveys to track individuals and document their microhabitat use in the mainstem Willamette River. 58 % of the lamprey were detected, representing 460 detections of 247 individuals across two years (2009 and 2010). Lamprey distributed significantly further upstream, and more were found in the main channel during a high flow year (2010) in comparison with a low flow year (2009). More lamprey held in the main channel across all river segments in 2010 than in 2009. Main channel habitats were significantly deeper than other microhabitats. Lamprey migrating into the upper river segment tended to use microhabitats other than the main channel. These other microhabitats included rock revetments and boulders/bedrock. Rock revetments were more prevalent in the middle – upper river segments, and a greater percentage of lamprey were associated with this microhabitat in these segments. The further upstream the lamprey migrated, the cooler, shallower, and faster water they encountered. One lamprey was associated with coolwater refuge (15.5 ^oC) in an alcove to the mainstem river (18.1 ^oC). We conclude that microhabitat use by pre-spawning Pacific lamprey differs by year (river flow), river segment, and availability in a large, regulated river.

通过预先产卵太平洋七lamp鳗（Entosphenus tridentatus），夏季河流流量的减少和水温的升高与保持行为有关。在主干威拉米特河（美国俄勒冈州）上。但是，尚不清楚这些七lamp鳗使用微栖息地（≤2 m）是否与特定的栖息地结构或避难所有关。我们将无线电标签植入七lamp鳗（n = 425）中，并进行了船只调查以追踪个人并记录他们在威拉米特河干流中的微生境。检测到58％的七lamp鳗，代表了两年（2009年和2010年）中247人的460次检测。Lamprey在上游明显分布，在高流量年份（2010年）与低流量年份（2009年）相比，在主渠道发现更多。与2009年相比，2010年所有河流段的主要河道中的七rey鳗数量都增加了。主要河道的生境比其他微生境要深得多。迁入上游河段的七鳗倾向于使用除主要河道以外的微生境。这些其他微生境包括岩石护岸和巨石/基岩。岩石护坡在中上游河流段更为普遍，并且在这些段中，与这些微生境相关的七lamp鳗比例更高。七lamp鳗向上游迁移的越远，它们遇到的水就越凉，越浅，越快。一只七lamp鳗与凉水庇护所有关（15.5 和他们遇到的更快的水。一只七lamp鳗与凉水庇护所有关（15.5 和他们遇到的更快的水。一只七lamp鳗与凉水庇护所有关（15.5^o C）在通往主干河（18.1 ^o C）的凹室中。我们得出的结论是，太平洋产于七flow鳗的产卵对微生境的使用因年份（河流量），河段和受管制的大河中的可用性而异。