A global assessment of fishes at lower abyssal and upper hadal depths (5000 to 8000 m)

The diversity of bait-attending fishes at lower abyssal and upper hadal depths was assessed using baited cameras in 14 subduction trenches, three fracture zones and two holes, spanning all five oceans. A total of 184 lander deployments from depths >5000 m (plus some additional observation from a submersible) were analysed to resolve the bathymetric extent of fishes and variations between locations. The most common families were the Macrouridae (grenadiers), Ophidiidae (cusk eels) and the Liparidae (snailfishes). Other less common families such as the Zoarcidae (eel pouts), Synphobranchidae (cut-throat eels) are reported, and the Stephanoberycidae (pricklefishes), and Ateleopodidae (jellynoses) were observed for the first time at hadal depths. While acknowledging many cryptic species and difficulty in identifying some groups from video, this study more than doubles the number of species and records of fishes at hadal depths and serves as an updated and illustrated collation of deepest fish records. We also discuss putative influences of temperature and oxygen on the depth range within the liparidae family, of which we found nine new species at hadal depths.