DFO Pacific Groundfish Synoptic Trawl Surveys - West Coast Haida Gwaii

The West Coast Haida Gwaii (WCHG) synoptic bottom trawl survey was first conducted annually from 2006 to 2008 and has since been repeated every second year on even numbered years. The survey was not impacted by the COVID-19 pandemic. This survey is one of a set of long-term and coordinated surveys that together cover the continental shelf and upper slope of most of the British Columbia coast. The other surveys are the Queen Charlotte Sound (QCS) survey, the Hecate Strait (HS) survey, the West Coast Vancouver Island (WCVI) survey, and the Strait of Georgia (SOG) survey. The objectives of these surveys are to provide fishery independent abundance indices of all demersal fish species available to bottom trawling and to collect biological samples of selected species. The survey follows a random depth-stratified design and the sampling units are 2 km by 2 km blocks.
The synoptic bottom trawl surveys are conducted by Fisheries and Oceans Canada (DFO) in collaboration with the Canadian Groundfish Research and Conservation Society (CGRCS), a non-profit society composed of participants in the British Columbia commercial groundfish trawl fishery. The Queen Charlotte Sound and West Coast Haida Gwaii surveys are conducted under collaborative agreements, with the CGRCS providing chartered commercial fishing vessels and field technicians, while DFO provides in-kind contributions for running the surveys including personnel and equipment. The Hecate Strait, West Coast Vancouver Island, and Strait of Georgia surveys are conducted by DFO and have typically taken place on the Canadian Coast Guard research vessel W.E. Ricker. In years when the W.E. Ricker has not been available, the Hecate Strait and West Coast Vancouver Island surveys have taken place on chartered industry vessels.
The data provided include information about the annual survey trips and fishing events (tows/sets) that are part of this survey series, including the vessel name, dates, times, spatial coverage, gear details, and effort information. Catch information (total weight in kg or counts of individual specimens) is included from successful fishing events. Catches are identified to species or to the lowest taxonomic level possible. Most catches are weighed, but some are too small (“trace” amounts) or too large (e.g. very large Big Skate). Some catches were subsampled and biological data were collected from individual fish specimens, including length, sex, and weight information. Where age structures were collected and processed, fish ages have been included. Relative abundance indices are provided for species that have been captured in every survey of the time series; however, we do not calculate a biomass index for the 2014 West Coast Haida Gwaii survey, as this survey was incomplete due to operational problems. The coefficient of variation and bootstrapped 95% confidence intervals are provided for each index. The groundfish data synopsis report (Anderson et al. 2019) provides an explanation of how the relative biomass indices are derived.

西海岸海达瓜依（West Coast Haida Gwaii, WCHG）同步底拖网调查于2006年至2008年首次每年开展一次，此后每逢偶数年每两年重复一次，且未受新冠疫情影响。该调查属于覆盖不列颠哥伦比亚省大部分大陆架与上陆坡的长期协同调查序列之一，其余调查包括夏洛特皇后湾（Queen Charlotte Sound, QCS）调查、赫卡特海峡（Hecate Strait, HS）调查、温哥华岛西海岸（West Coast Vancouver Island, WCVI）调查以及乔治亚海峡（Strait of Georgia, SOG）调查。此类调查的核心目标是为所有可开展底拖网作业的底层鱼类提供渔业独立丰度指数，并采集选定物种的生物样本。本调查采用随机深度分层设计，采样单元为2千米×2千米的区块。
本同步底拖网调查由加拿大渔业与海洋部（Fisheries and Oceans Canada, DFO）联合加拿大底层鱼类研究与保护协会（Canadian Groundfish Research and Conservation Society, CGRCS）实施，该协会是由不列颠哥伦比亚省商业底层鱼类拖网渔业从业者组成的非营利组织。其中夏洛特皇后湾与西海岸海达瓜依调查依托合作协议开展：CGRCS提供包租的商业捕捞船舶与现场技术人员，DFO则以人力、设备等实物形式承担调查运行相关投入。赫卡特海峡、温哥华岛西海岸以及乔治亚海峡调查由DFO主导，通常搭载加拿大海岸警卫队W.E.里克特号（W.E. Ricker）研究船执行；若该船无法投入使用，则采用包租的行业船舶开展赫卡特海峡与温哥华岛西海岸调查。
本次公开的数据涵盖本调查序列中的年度航次与捕捞作业（拖网/放网）信息，包括船舶名称、作业日期、作业时间、空间覆盖范围、渔具细节与作业强度数据。成功捕捞作业的渔获信息（以千克计的总重量或个体标本计数）也包含在内。所有渔获均被鉴定至物种级别或尽可能低的分类学层级。多数渔获已完成称重，但部分因体量过小（"trace" 渔获）或过大（如巨型大鳐）未进行称重。部分渔获被进行子采样，并从个体标本中采集了体长、性别与体重等生物数据。若完成了年龄结构的采集与处理，则同步提供鱼类年龄数据。
针对时间序列中每一次调查均捕获的物种，本数据集提供其相对丰度指数；但2014年西海岸海达瓜依调查因作业问题未完成，故未计算该次调查的生物量指数。每个指数均附带变异系数与bootstrap法计算的95%置信区间。《底层鱼类数据概要报告》（Anderson等，2019）对相对生物量指数的推导方法进行了详细说明。