Data from: Shortspine thornyhead and rockfish (Scorpaenidae) distribution in response to substratum, biogenic structures and trawling

Learmonth Bank in northern British Columbia sustains an active trawl fishery that returns large bycatches of deep-sea sponges and corals. To examine effects of biogenic structures on the distribution of fish, we examined nearly 30 km of high-definition imagery from a remotely operated vehicle and documented locations of 2770 scorpaenid fish. The 2 local genera have similar abundances, averaging about 1.2 individuals 100 m–2, but have different spatial abundance patterns: shortspine thornyhead Sebastolobus alascanus are randomly distributed on featureless substrata and their abundance increases with depth. Rockfish Sebastes spp. associate with higher seafloor relief nonrandomly and select for sponges and corals over the inert substrata alone; 95% of the rockfish occurred on 27% of the seafloor surveyed. Sponges (Demospongia and Hexactinellida) were abundant on the bedrock and boulders of the bank and adjacent moraine and covered 30 to 55% of the seafloor compared with 1% of the sediment and aggregates of the surrounding basin. The majority of rockfish (80%) occurred with sponges ≥50 cm in height, and even beds of short sponges attracted 4 times as many rockfish than did substrata with no large epifauna. While over half of primnoid corals over 30 cm tall had associated rockfish, less than 2% of the seafloor had large coral, and small coral had no associated rockfish. On the adjacent seafloor with past trawling activity, Primnoa pacifica was 13 times less abundant, and large corals and sponges were rare. Thornyhead abundance doubled but rockfish had a 3-fold reduction in numbers. Our study indicates that degradation of biogenic structures is a long-term detriment to rockfish species and, although the mechanism remains unclear, our data suggest it occurs through the destruction of a habitat that is more effective for shelter than rough inert seafloor.位于不列颠哥伦比亚省北部的利尔蒙斯沙洲（Learmonth Bank）拥有活跃的拖网渔业，其作业伴随大量深海海绵与珊瑚作为副渔获物。为探究生物成因构造（biogenic structures）对鱼类分布的影响，本研究分析了遥控水下机器人（Remotely Operated Vehicle, ROV）采集的近30公里高清影像序列，记录了2770尾鲉科鱼类（scorpaenid fish）的分布点位。该区域的2个本地属鱼类丰度相近，平均密度约为1.2尾/100 m²，但空间分布模式存在显著差异：短棘平头鲉（Sebastolobus alascanus）在平坦无特征的底质上呈随机分布，其丰度随水深增加而升高；岩鱼（Sebastes spp.，平鲉属物种）则非随机地聚集于海底地形起伏较高的区域，相较于单纯的惰性底质，它们更偏好栖息于附着有海绵与珊瑚的区域——95%的岩鱼仅分布在本次调查海域中27%的海底区域内。 海绵涵盖寻常海绵纲（Demospongia）与六放海绵纲（Hexactinellida），在沙洲及邻近冰碛物的基岩与巨砾上分布广泛，其覆盖的海底面积达30%~55%；而在周边海盆的沉积物与团聚体区域，海绵覆盖率仅为1%。绝大多数岩鱼（80%）栖息在高度≥50 cm的海绵附着区域，即便是低矮的海绵床，所能吸引的岩鱼数量也比无大型底上动物（epifauna）的底质区域高出4倍。尽管超过一半高度超过30 cm的柳珊瑚科（Primnoidae）珊瑚伴生有岩鱼，但整体仅不到2%的海底区域存在大型珊瑚，且小型珊瑚未发现有岩鱼伴生。 在邻近曾开展拖网作业的海底区域，太平洋扇珊瑚（Primnoa pacifica）的丰度仅为未受干扰区域的1/13，大型珊瑚与海绵也极为稀少；与此同时，平头鲉的丰度翻倍，但岩鱼种群数量却下降了3倍。本研究表明，生物成因构造的退化对岩鱼种群存在长期负面影响，尽管具体作用机制尚不明晰，但研究数据显示，该影响源于岩鱼失去了比粗糙惰性海底更有效的庇护栖息地。