Daily salmon escapement counts, Central Region, Alaska

As salmon migrate from the marine environment to freshwater streams to spawn, a certain number are allowed to pass through, or '/escape/' the salmon fishery (frequently located near the mouth of the freshwater stream) as a management strategy to preserve the species. Escapement data are the enumeration of these migrating fish as they pass upstream, and represent an index of the total abundance of spawning salmon in that particular stream. These data are important for fisheries management, since most salmon harvest occurs in freshwater rivers during this migration. Escapement data are collected in a variety of ways. Stationary projects utilize observers stationed along freshwater corridors who count salmon as they pass upriver through weirs or past elevated towers. Sonar equipment placed in the river can also give a stationary escapement count. These counts usually represent a sample, and are expanded to represent a 24h period. Escapement data can also be collected using aerial surveys, where observers in an aircraft provide an index to estimate escapement. In general, escapement counts do not represent total abundance, but instead an index of abundance. Surveys are usually timed to coincide with peak spawning activity, generally in the summer, but in the case of Coho salmon in the fall as well. Some data about non-salmon species are also included. This dataset contains salmon escapement data from the Central Region (Region II) which includes Bristol Bay, Prince William Sound, and Cook Inlet.当鲑鱼从海洋洄游至淡水溪流产卵时，作为保护该物种的管理策略，会允许一定数量的个体通过鲑鱼渔场（通常设于淡水溪流入海口附近），即所谓的“逃逸（escape）”。逃逸量数据（escapement data）是对这些向上游洄游的个体进行的计数，可作为特定溪流中产卵鲑鱼总丰度的量化指标。此类数据对渔业管理至关重要，因为绝大多数鲑鱼捕捞活动都发生在该洄游阶段的淡水河道中。逃逸量数据的采集方式多种多样：固定监测项目会安排观测人员驻守在淡水河道沿线，计数通过堰坝或高架观测塔向上游洄游的鲑鱼；布设在内河的声呐设备同样可开展固定站点的逃逸量计数。此类计数结果通常仅为抽样数据，需经推算以覆盖单日（24h）的总量。逃逸量数据也可通过航空调查采集，机载观测人员通过观测估算逃逸量，以此作为丰度指标。总体而言，逃逸量计数结果并非总丰度的直接统计值，而是丰度的替代指标。调查通常会安排在产卵活动高峰期开展，多数为夏季；对于银鲑（Coho salmon），则也会在秋季开展相关调查。本数据集同时包含部分非鲑鱼物种的相关数据。本数据集涵盖中部区域（Region II）的鲑鱼逃逸量数据，该区域包含布里斯托尔湾（Bristol Bay）、威廉王子湾（Prince William Sound）与库克湾（Cook Inlet）。