DFO Newfoundland and Labrador Region Ecosystem Trawl Surveys

An OBIS version of the Fisheries and Oceans Canada Newfoundland and Labrador region (DFO-NL) ecosystem trawl survey data from 1977-2011. Survey data are collected by DFO stock assessment staff during stratified random seasonal (spring and fall) bottom trawl surveys. These surveys were initially designed to estimate abundance and distribution of commercial groundfish species, but since 1995 have also been regularly recording non-commercial species and invertebrates. The area surveyed has varied over time, as has the trawl gear used and the fishing methodology (tow duration) employed. Note in some years the ‘fall’ survey (usually Oct-Dec), continued January of the following calendar year. This dataset is the OBIS version of the 'bottom trawl' dataset and only species presence information is included at this time for standard sets. Taxonomic limitations Due to the emphasis on commercial fish species, taxonomic classifications of non-commercial fish and invertebrates prior to 1995 were frequently limited to genus or family and sometimes order. With the introduction of the Campelen trawl came a major change in the taxonomic detail recorded and by 2008 efforts were made to identify all fish to species, when possible. However although improved, identifications of some invertebrate taxa continue to be recorded at higher taxonomic levels. Consequently the absence of records for a particular species cannot be equated with an absence of the species, particularly when higher taxonomic classifications are present.本数据集为1977-2011年加拿大渔业与海洋部纽芬兰与拉布拉多省区域（DFO-NL）生态系统拖网调查数据的海洋生物地理信息系统（Ocean Biogeographic Information System，OBIS）版本。该调查数据由DFO种群评估人员在分层随机季节性（春季与秋季）底拖网调查期间采集。此类调查最初旨在估算商业性底栖鱼种的丰度与分布范围，但自1995年起，也开始定期记录非商业性物种与无脊椎动物。调查区域、所用拖网渔具及作业方法（拖曳时长）均随时间发生变化。请注意，部分年份的“秋季”调查（通常为10月至12月）会延续至次年1月。 本数据集为"底拖网"数据集的OBIS版本，目前仅包含标准站位的物种存在信息。 分类学局限性 由于调查最初聚焦于商业鱼类，1995年之前的非商业鱼类与无脊椎动物的分类学归类通常仅能达到属或科水平，部分类群甚至仅能达到目水平。随着卡佩伦拖网（Campelen trawl）的引入，记录的分类学细节发生了重大变化；至2008年，相关团队已尽可能将所有鱼类鉴定至物种水平。尽管分类精度有所提升，但部分无脊椎动物类群的鉴定结果仍仅记录为更高的分类阶元。因此，某一物种未被记录并不等同于该物种不存在，尤其当仅存在更高分类阶元的记录时更是如此。