Interagency Ecological Program San Francisco Estuary Spring Kodiak Trawl Survey 2002 - 2020

The Interagency Ecological Program San Francisco Estuary Spring Kodiak Trawl Survey was initiated by the California Department of Fish and Wildlife (CDFW) in 2002 to improve the detection rate of pre-spawning and mature Delta Smelt (hypomesus transpacificus). The survey began as the Spring Midwater Trawl Survey, an extension of the Fall Midwater Trawl Survey, in 1991 to assist with water management and export decisions in relation to the distribution of pre-spawning Delta Smelt. Net evaluations studies compared the relative catch efficiency of 3 types of nets and found that the Kodiak net was most effective for Sampling adult Delta Smelt. Objectives of SKT are to improve the ability to detect Delta Smelt, obtain maturity status for adult Delta Smelt, and provide results to scientist and managers on a near real-time basis to ais in resource management. SKT operates 6 monthly surveys December through May each lasting 4-5 days in length. Each survey, 40 fix sample locations are sampled using a standard 10 minute Kodiak trawl with a total length of 65 feet and a fully expanded mouth opening of 25 feet by 6 feet. The volume of water sampled is estimated using a General Oceanics flowmeter placed over the side of the boat. The net is constructed of green or black variable mesh ranging in dimension from 2 inches knoteted stretched mesh at the mouth and decreasing by ½ inch through a series of 5 panels to ¼ inch knotless stretched mesh at the cod-end. All fish sampled are identified to species and enumeration, Delta Smelt are staged in the field. At each station, environmental and water quality data are also collected, and include: temperature, electrical conductivity (normalized @ 25°C), water clarity, and tidal condition.

跨机构生态项目旧金山河口春季科迪亚克拖网调查由加利福尼亚州鱼类与野生动物局（California Department of Fish and Wildlife, CDFW）于2002年启动，旨在提升对产卵前及成熟三角洲胡瓜鱼（Delta Smelt, Hypomesus transpacificus）的检出率。该调查的前身是1991年设立的春季中层拖网调查——作为秋季中层拖网调查的延伸项目，其最初目的是辅助制定与产卵前三角洲胡瓜鱼分布相关的水资源管理及外调决策。网具评估研究对比了三种拖网的相对捕捞效率，结果显示科迪亚克拖网在采样成年三角洲胡瓜鱼时效果最优。本次SKT（春季科迪亚克拖网调查）的目标包括：提升三角洲胡瓜鱼的检出能力、获取成年三角洲胡瓜鱼的成熟状态信息，并以近乎实时的方式向科研人员与管理人员反馈调查结果，以辅助自然资源管理工作。SKT每年12月至5月开展6次月度调查，每次调查持续4至5天。每次调查将布设40个固定采样点位，采用标准10分钟时长的科迪亚克拖网进行采样，该拖网总长65英尺，完全展开的网口尺寸为25英尺×6英尺。采样水体体积通过安装在船舷的通用海洋学（General Oceanics）流量计进行估算。该拖网采用绿色或黑色可变网目尺寸的网衣制作：网口处为2英寸有结拉伸网目，通过5组网片依次以每级缩减½英寸的方式过渡，最终在网囊处变为¼英寸无结拉伸网目。所有采样获取的鱼类均会进行物种鉴定与数量统计，三角洲胡瓜鱼会在野外完成成熟度分级。在每个采样站位，调查人员还会同步收集环境与水质数据，具体包括水温、电导率（归一化至25℃）、水体透明度以及潮汐状况。