North Temperate Lakes LTER: Fish Length Frequency 1981 - current

This data set is a derived data set based on fish catch and length data. Data are collected annually to enable us to track the fish assemblages of eleven primary lakes (Allequash, Big Muskellunge, Crystal, Sparkling, Trout, bog lakes 27-02 [Crystal Bog] and 12-15 [Trout Bog], Mendota, Monona, Wingra and Fish). Sampling on Lakes Monona, Wingra, and Fish started in 1995; sampling on other lakes started in 1981. Sampling is done at six littoral zone sites per lake with seine, minnow or crayfish traps, and fyke nets; a boat-mounted electrofishing system samples three littoral transects. Vertically hung gill nets are used to obtain two pelagic samples per lake from the deepest point. A trammel net samples across the thermocline at two sites per lake. In the bog lakes only fyke nets and minnow traps are deployed. Parameters measured include species-level identification and lengths for all fish caught, and scale samples and weight from a subset. Derived data sets include species richness, catch per unit effort, and size distribution by species, lake, and year. Dominant species vary from lake to lake. Perch, rockbass, and bluegill are common, with walleye, large and small mouth basses, northern pike and muskellunge as major piscivores. Cisco have been present in the pelagic waters of four lakes, and the exotic species, rainbow smelt, is present in two. The bog lakes contain mudminnows. Protocol used to generate data: The number of fish caught in each five mm length interval (0<length<5, 5<=length<10, etc.) have been summed over gear. In cases in which only a random subsample of fish were measured, the unmeasured fish have been assigned to the length categories based on the proportions in length categories for the measured fish of the subsample. Day seines were only used in 1981 and have been eliminated from this data set to make sampling effort across years comparable. The only sampling done in 2020 were a single gill-netting replicate in Sparkling, Crystal, and Trout lakes. Sampling in Fish Lake was suspended in 2021 due to significant lake level changes. Sampling Frequency: annually. Number of sites: 11 Please consult NTL's website for information on experimental lake manipulations and the DNR's website for management activities

本数据集为基于鱼类捕捞量与体长数据衍生而来的数据集，每年开展数据采集工作，用于追踪11个主要湖泊的鱼类群落组成，这些湖泊包括阿莱夸什湖（Allequash）、大熊狗鱼湖（Big Muskellunge）、克里斯托湖（Crystal）、斯帕克林湖（Sparkling）、特劳特湖（Trout）、27-02号泥炭湖（Crystal Bog）、12-15号泥炭湖（Trout Bog）、门多塔湖（Mendota）、莫诺纳湖（Monona）、温格拉湖（Wingra）与费什湖（Fish）。

莫诺纳湖（Monona）、温格拉湖（Wingra）与费什湖（Fish）的采样工作始于1995年，其余湖泊的采样则于1981年启动。每个湖泊设置6个沿岸带（littoral zone）采样位点，采用围网（seine）、小型渔笼（minnow trap）、螯虾陷阱与袋形渔笼（fyke nets）开展采样；同时使用船载电捕鱼系统（boat-mounted electrofishing system）对3条沿岸样带进行采样。采用垂直悬挂刺网（gill nets）在每个湖泊的最深点位采集2个远洋带（pelagic zone）样本；使用三重刺网（trammel net）在每个湖泊的2个位点跨越温跃层（thermocline）进行采样。泥炭湖仅部署袋形渔笼与小型渔笼开展采样。

本次采集的测量参数包括所有捕获鱼类的物种鉴定结果与体长数据，以及部分个体的鳞片样本与体重数据。衍生数据集包含物种丰富度、单位捕捞努力量渔获量（catch per unit effort），以及按物种、湖泊与年份划分的体长分布。

各湖泊的优势物种存在差异：鲈鱼（Perch）、岩鲈（rockbass）与蓝鳃太阳鱼（bluegill）为常见物种，大眼梭鲈（walleye）、大口黑鲈、小口黑鲈、白斑狗鱼（northern pike）与北美狗鱼（muskellunge）为主要肉食性鱼类。湖白鲑（Cisco）曾出现在4个湖泊的远洋水域，外来物种彩虹胡瓜鱼（rainbow smelt）则分布于2个湖泊中。泥炭湖含有泥小鱼（mudminnows）。

数据集生成规程如下：将每个5mm体长区间（0<体长<5mm、5≤体长<10mm等）内的捕获鱼类数量按渔具类型汇总。若仅对部分鱼类开展了随机抽样测量，则未测量的个体将根据抽样测量个体的体长区间占比，被分配至对应体长区间。日间围网（day seines）仅在1981年使用过，为保证年度采样努力量（sampling effort）可比，该采样方式已从本数据集中移除。2020年仅在斯帕克林湖（Sparkling）、克里斯托湖（Crystal）与特劳特湖（Trout）各完成1次刺网重复采样。费什湖（Fish）的采样工作于2021年因湖水位显著变化暂停。

采样频率：每年1次。采样位点总数：11个。有关湖泊实验调控的详细信息，请参阅NTL官网；有关湖泊管理活动的信息，请参阅DNR官网。