Steelhead Monitoring Data

Each fall, the Juvenile Steelhead & Stream Habitat (JSSH) monitoring program measures population density and assesses habitat quality for steelhead across four watersheds in Santa Cruz county. Within each watershed, different sections of stream, known as reaches, are defined based on similar characteristics such as: gradient, channel width, substrate, and habitat types. Fish and habitat sampling is conducted along half-mile stream segments within each reach. Each half-mile stream segment is habitat typed to assess stream conditions. Habitat typing involves identifying specific habitat units (riffles, runs, pools), measuring stream depth and width, and assessing substrate and cover. Fish sampling sites are chosen based on average habitat quality within a segment, with a focus on pool length, depth, and cover. A typical sampling site consists of two pools and any adjacent runs and riffles. Sampling sites differ in total length due to the unique composition of pool, riffle, and run habitats. To compare steelhead counts across sites, the JSSH program reports steelhead density: the total number of steelhead per 100 feet of stream. The steelhead densities include both the counted (captured) steelhead and an estimate of any steelhead that may have evaded capture. The number of escaped fish are estimated with a formula based on the rate of capture from the electrofishing process. For the best chance to survive to adulthood, steelhead need to be at least 150mm when they migrate to the ocean in spring.The JSSH program measures steelhead in autumn and assumes that fish longer than 75mm will be big enough by spring to migrate to the ocean. Fish that are smaller than 75mm in autumn will likely need an additional year in freshwater to grow before migration. Due to these important size constraints, JSSH reports steelhead density for two size classes: steelhead that are shorter than 75mm and steelhead 75mm or longer.每年秋季，幼年硬头鳟与溪流栖息地（Juvenile Steelhead & Stream Habitat, JSSH）监测项目都会对圣克鲁斯县境内四个流域的硬头鳟种群密度开展测算，并对其栖息地质量进行评估。 在每个流域内，研究人员会根据坡度、河道宽度、底质以及栖息地类型等相似特征，将溪流划分为不同的河段（reaches）。 每个河段内均会沿半英里长的溪流片段开展鱼类与栖息地采样。每一段半英里溪流片段都会进行栖息地类型划分，以评估溪流整体状况。 栖息地类型划分工作包括识别特定的栖息地单元（浅滩（riffles）、平流段（runs）、深潭（pools）），测量溪流深度与宽度，并评估底质与遮蔽物情况。 鱼类采样点位会根据片段内的平均栖息地质量选定，重点考量深潭长度、深度以及遮蔽物情况。典型采样点位包含两处深潭，以及毗邻的平流段与浅滩。 由于深潭、浅滩与平流段的栖息地组成各不相同，各采样点位的总长度也存在差异。为了对不同点位的硬头鳟数量进行对比，JSSH项目会报告硬头鳟种群密度：即每100英尺溪流内的硬头鳟总数量。 该种群密度统计既包含已计数（捕获）的硬头鳟，也会估算可能逃脱捕获的硬头鳟数量。逃逸个体的数量会基于电捕鱼过程中的捕获率，通过特定公式进行估算。 硬头鳟若要获得最高的成体存活率，需在春季洄游至海洋时体长至少达到150毫米。 JSSH项目于秋季开展硬头鳟监测，并假设体长超过75毫米的个体可在春季前长至足够体型，完成海洋洄游；而秋季体长不足75毫米的个体，则大概率需要在淡水环境中多生长一年，再进行洄游。 基于上述关键的体长限制条件，JSSH项目会按两个体长等级分别报告硬头鳟种群密度：体长不足75毫米的硬头鳟，以及体长75毫米及以上的硬头鳟。