Afognak Lake Sockeye Salmon Monitoring Project (2020–2022)

Weir Installation and Adult Salmon Enumeration A 27 m long weir was installed perpendicular to the stream flow and consisted of 10 wooden tripods (each tripod consisting of three 4″ x 4″ x 8′ spruce timbers and 2″ x 6″ x 6′ horizontal cat-walk supports), 33 aluminum pipes (2″ x 10′), 44 picketed aluminum panels (1″ aluminum pipe with 1″ spacing totaling 30″ x 6′), and 2 framed panel gates. All materials were secured with sandbags and lashed together to create a fish-tight structure that conformed to the contour of the stream channel. Two counting gates were placed between panels in the two deepest channels of the river enabling fish to be counted as they pass through the weir. A white flash panel was placed on the substrate beneath each gate to enhance visibility and species identification. Fish were counted by field technicians using hand tally denominators as fish migrated upstream through the gates. The counting gates remained closed until staff were present to count fish through the weir for escapement enumeration or when fish were being collected into the live trap for age, sex, and length sampling (ASL). Age, Sex, and Length Sampling An upstream “Scott live trap” (local name for a modified trap capable of capturing steelhead) was installed in front of the east bank gate, which acted as a sampling trap as well as a downstream steelhead trap. The trap consisted of 6 weir panels placed horizontally in the river in the form of a diamond. Adult sockeye salmon were sampled at the weir site throughout the adult escapement. Details and procedures for adult sampling are outlined in the Kodiak Management Area Sockeye Salmon Catch and Escapement Sampling Operational Plan, 2022. All scales, when possible, were collected from the preferred area of each fish. Scales were mounted on scale “gum” cards and returned to the Kodiak ADF&G office where impressions were made on cellulose acetate. Fish ages were determined by examining scale impressions for annual growth increments using a microfiche reader fitted with a 60X lens following designation criteria established by Mosher 1968. Ages were recorded using European notation, where a decimal separates the number of winters spent in fresh water (after emergence) from the number of winters spent in salt water (e.g., 2.3). The total age of the fish includes an additional year representing the time between egg deposition and emergence of fry. Length measurements were taken from mid-eye to tail fork to nearest 1 mm and sex was determined from external morphological characteristics. On days where escapement occurred but no samples were collected, proportions were estimated by linear interpolation between sampling events. The sample size was selected so that the proportion of each major age group (by stratum) was estimated within at least α=0.07 of its true value 95% of the time. Standard error of the age proportions was calculated as the square root of estimated variance of a proportion. Average length (unweighted) was calculated by age and sex.一、堰体安装与成年鲑鱼计数 本次布设的堰体长27米，垂直于水流方向安装，由以下部件组成：10组木质三脚架（每组三脚架含3根4英寸×4英寸×8英尺的云杉木料，以及2英寸×6英寸×6英尺的横向人行步道支撑）、33根铝管（2英寸×10英尺）、44块带围栏铝板（采用1英寸铝管制作，管间距1英寸，单块尺寸30英寸×6英尺），以及2块带框面板闸门。所有构件通过沙袋固定并绑扎连接，形成贴合河道轮廓的阻鱼密闭结构。 两道计数闸门设置在河道两处最深航道的面板之间，使得鱼类通过堰体时可被计数。每道闸门下方的河床基底均布设白色反光面板，以提升可视性与物种识别效率。野外技术人员采用手持计数器，在鱼类溯游通过闸门时完成计数。计数闸门保持关闭状态，仅当工作人员到场开展堰体洄游量计数，或需将鱼类收集至活捕装置开展年龄、性别与体长采样（Age, Sex, Length, ASL）时才会开启。 二、年龄、性别与体长采样 东岸闸门前方布设了上游Scott活捕装置（Scott live trap，当地俗称，为用于捕获钢头鳟的改良式捕集装置），该装置兼具采样捕集与下游钢头鳟捕集功能。装置由6块堰体面板以菱形形式横向布设于河道中。 整个成年洄游季均在堰体点位开展成年红大麻哈鱼（sockeye salmon）采样。成年采样的细节与流程详见《2022年科迪亚克管理区域红大麻哈鱼捕捞与洄游量采样作业计划》。尽可能从每尾鱼的优选的鳞片采集部位获取鳞片样本，将鳞片固定于鳞片胶卡上后，送至阿拉斯加州渔猎部（Alaska Department of Fish and Game, ADF&G）科迪亚克分局办公室，在醋酸纤维素片基上制作鳞片印模。鱼类年龄通过配备60倍镜头的缩微胶片阅读器，依据Mosher 1968年制定的判定标准，观察鳞片印模的年度生长纹确定。年龄采用欧洲记法记录，以小数点分隔淡水（孵化后）越冬次数与海水越冬次数（例如：2.3）。鱼类总年龄需额外增加1年，对应卵沉积至鱼苗孵化的时长。 体长测量取眼中点至尾叉间距，精确至1毫米；性别通过外部形态特征判定。 在发生洄游但未开展采样的日期，通过相邻采样事件间的线性插值估算当日的采样比例。样本量设定原则为：95%的置信度下，各按层划分的主要年龄组的比例估算误差不超过α=0.07。年龄比例的标准误按比例估算方差的平方根计算。按年龄与性别分组计算未加权平均体长。