Juvenile salmonid rotary screw trap data from Battle and Clear Creeks, Shasta and Tehama Counties, California.

Clear Creek The U.S. Fish and Wildlife Service continued its juvenile salmonid
monitoring project in Clear Creek, Shasta County, California, that
began in December 1998 using a rotary screw trap (RST) located at
river mile (RM) 1.7. This monitoring project has three primary
objectives: (1) calculate annual juvenile passage indices for
Chinook Salmon Oncorhynchus tshawytscha and Rainbow
Trout/steelhead O. mykiss (we use the term O. mykiss to refer to
both the stream resident (Rainbow Trout) and anadromous
(steelhead) life histories because of the difficulties in
differentiating the anadromous and resident forms in the field)
for inter-year comparisons and analyses of the effectiveness of
stream restoration activities; (2) obtain juvenile salmonid life
history information including size, timing, and potential factors
limiting survival; and (3) collect biological samples from
juvenile salmonids. Chinook Salmon run classifications show that
all Chinook Salmon runs known to the Sacramento River were
captured; however, due to overlapping spawning times of spring-run
and fall-run Chinook Salmon it was problematic to index the
juvenile passage using only the RST at RM 1.7. Since 2003 a
separation weir has been used to isolate adult spring-run Chinook
Salmon from adult fall-run Chinook Salmon; therefore, a second RST
was added above the weir at RM 8.4. Battle Creek The U.S. Fish and Wildlife Service continued its juvenile salmonid
monitoring project in Battle Creek, Shasta and Tehama Counties,
California, that began in December 1998 using a RST located at
river mile (RM) 6.2. The upper Battle Creek RST objectives are to
(1) calculate annual juvenile passage indices for spring-run,
late-fall run, and winter-run Chinook Salmon; Rainbow
Trout/steelhead O. mykiss (we use the term O. mykiss to refer to
both the stream resident (Rainbow Trout) and anadromous
(steelhead) life histories because of the difficulties in
differentiating the anadromous and resident forms in the field);
(2) obtain juvenile salmonid life history information including
size, timing, and potential factors limiting survival; and (3)
collect biological samples from juvenile salmonids. Chinook Salmon
run designations in the Sacramento River watershed were developed
using length-at-date criteria for Sacramento River fall-run
Chinook Salmon. These designations may not be accurate when used
for salmon captured in tributaries of the Sacramento River; these
streams have variable and overlapping run timing of spring-run and
fall-run Chinook Salmon. After 2008 all fall-run designated
Chinook Salmon were reassigned as spring-run in the spring-run
Chinook Salmon passage indices as preventative measures were taken
to reduce the potential for fall-run Chinook Salmon to enter the
upper watershed (above the Coleman National Fish Hatchery barrier
weir). Mark–recapture trials Since the RST only captures fish from a small portion of the creek
cross section, it is necessary to implement a method to project
the RST catch numbers to portions of the creek outside of the RST
capture zone. Mark–recapture trials were attempted, when creek
conditions were conducive for such studies and when fish numbers
allowed, to determine the efficiency of the RSTs to catch juvenile
salmonids moving downstream during a given time period. If one or
no mark–recaptures trials were conducted, then the historic
monthly and global averages were used to calculate that passage
indices. Mark-recapture–trials on Battle Creek are conducted using
hatchery-origin fish (from Coleman National Fish Hatchery), while
on Clear Creek natural-origin fish are used. Fish used for the
trials were either single or dual marked. For the single mark
trials the fish were stained with Bismarck brown-Y. Dual marked
fish clipped with surgical scalpels, removing an area of
approximately 1–2 mm^2 from the tip of either the upper or lower
lobe of the caudal fin and then the fish were stained as above. Note: data within the current year’s monitoring season are
considered provisional. The monitoring season typically concludes
at the end of September.

克利尔溪（Clear Creek）
美国鱼类和野生动物管理局（U.S. Fish and Wildlife Service）继续推进其在加利福尼亚州沙斯塔县克利尔溪开展的幼鲑监测项目，该项目自1998年12月启动，采用位于河英里（river mile, RM）1.7处的旋转螺旋诱捕器（rotary screw trap, RST）进行采样。本监测项目共有三项核心目标：（1）计算奇努克鲑（Chinook Salmon，*Oncorhynchus tshawytscha*）与虹鳟/钢头鳟（Rainbow Trout/steelhead，*O. mykiss*，本文采用*O. mykiss*一词同时指代陆封型溪流定居虹鳟与溯河洄游型钢头鳟，因野外难以区分这两种生态型）的年度幼鱼通过指数，用于年际对比及溪流修复活动效果分析；（2）获取幼鲑的生活史信息，包括体长、洄游时间及潜在的生存限制因子；（3）采集幼鲑的生物样本。监测结果显示，本次捕获了萨克拉门托河已知的所有奇努克鲑洄游类群，但由于春型与秋型奇努克鲑的产卵时间存在重叠，仅依靠RM 1.7处的RST开展幼鱼通过指数计算存在较大难度。自2003年起，项目组采用分隔堰将成年春型奇努克鲑与成年秋型奇努克鲑分离，因此在RM 8.4处的堰体上方增设了第二台RST。

巴特尔溪（Battle Creek）
美国鱼类和野生动物管理局继续推进其在加利福尼亚州沙斯塔县与特哈马县巴特尔溪开展的幼鲑监测项目，该项目自1998年12月启动，采用位于河英里（RM）6.2处的RST进行采样。巴特尔溪上游RST的监测目标为：（1）计算春型、晚秋型与冬型奇努克鲑，以及虹鳟/钢头鳟（*O. mykiss*，本文采用*O. mykiss*一词同时指代陆封型溪流定居虹鳟与溯河洄游型钢头鳟，因野外难以区分这两种生态型）的年度幼鱼通过指数；（2）获取幼鲑的生活史信息，包括体长、洄游时间及潜在的生存限制因子；（3）采集幼鲑的生物样本。萨克拉门托河流域的奇努克鲑洄游类群划分标准基于萨克拉门托河秋型奇努克鲑的体长-日期判定准则，该标准应用于萨克拉门托河支流捕获的鲑鱼时可能存在偏差，因这些支流的春型与秋型奇努克鲑洄游时间存在差异且相互重叠。2008年后，为降低秋型奇努克鲑进入上游流域（科尔曼国家鱼类孵化场（Coleman National Fish Hatchery）拦河堰以上区域）的风险，项目组采取了预防性措施，因此所有被标记为秋型的奇努克鲑在春型奇努克鲑幼鱼通过指数中被重新归类为春型。

标记重捕试验（Mark–recapture trials）
由于RST仅能捕获溪流断面局部区域的鱼类，因此需要通过特定方法将RST的捕获量外推至诱捕区以外的溪流区域。当溪流条件适宜且鱼类种群数量允许时，项目组开展了标记重捕试验，以测定RST在特定时段内捕获下游洄游幼鲑的效率。若当年开展的标记重捕试验次数少于1次或仅开展1次，则采用历史月度及全局平均值计算幼鱼通过指数。巴特尔溪的标记重捕试验采用孵化场来源的鱼类（源自科尔曼国家鱼类孵化场），而克利尔溪的试验则采用野生来源的鱼类。试验用鱼分为单标记与双标记两类：单标记组的鱼类采用俾斯麦棕-Y（Bismarck brown-Y）进行染色标记；双标记组的鱼类先用手术手术刀切除尾鳍上叶或下叶尖端约1~2 mm²的组织，随后采用与单标记组相同的方式进行染色。

注：本年度监测季内的数据均为暂定数据。监测季通常于每年9月底结束。