DOI: 10.5061/dryad.s611n
title: Data from: Shortspine thornyhead and rockfish (Scorpaenidae) distribution in response to substratum, biogenic structures and trawling

description: 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.
description: CHONe_MB-18_DuPreezC_dataThe spatial distribution of Scorpaenidae fish (thornyhead and rockfish), deep-sea sponges and corals, substratum types, and trawling evidence on and around Learmonth Bank, British Columbia (from Du Preez and Tunnicliffe 2011). Additional data collected and included in this data package, but not used in the original publication, include: distribution of other benthic fish (e.g., skates and flatfish), some invertebrates, sediment types (with percent coverage), and ROV operational information. All biotic and abiotic seafloor data were collected from the annotation of benthic video surveys (Table 1) conducted by the remotely operated vehicle (ROV) ROPOS (navigational data included as Table 2). Data attributes and definitions are also provided. This is was a Canadian Healthy Oceans Network (CHONe) Marine Biodiversity Project, MB-18.Table_1_video_annotation.txtROV navigationThe benthic video surveys (Table 1) were conducted by the remotely operated vehicle (ROV) 'ROPOS'. The video annotation data and ROV navigation (for georeferencing) are linked by LogIDs.Table_2_ROV_navigation.txtData attributes and definitionsTables detailing the attributes and definitions of data in Table_1_video_annotation.txt and Table_2_ROV_navigation. txt.Data_attributes_&_definitions.docx