Bathyal demersal fishes of the Charlie-Gibbs Fracture Zone region (49°–54°N) of the Mid-Atlantic Ridge: III. Results from remotely operated vehicle (ROV) video transects

Thomas D Linley,Claudia H.S Alt,Daniel O.B Jones,Imants G Priede

doi:10.1016/j.dsr2.2013.08.013

Thomas D Linley, Claudia H.S Alt + Show 2 more

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https://doi.org/10.1016/j.dsr2.2013.08.013

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Abstract

Demersal fish were assessed by remotely operated vehicle (ROV) video transects at sites to the NE, NW (54°N), SE and SW (49°N) of the Charlie-Gibbs Fracture Zone (CGFZ) at ca. 2500m depth on the Mid-Atlantic Ridge. At each site, three different slope categories (flat, 10° slope and >30° slope) were sampled with four transects, each surveying 2000m3 of suprabenthic water. This resulted in 12 high-definition video transects at every site, covering a total of 24,000m3 suprabenthic water. Six species were observed; which was fewer than in surveys using baited landers (19 species) and trawls (26 species) in the same area. Bathysaurus ferox, Halosauropsis macrochir, Antimora rostrata and Polyacanthonotus challengeri did not vary in density between sites, while Coryphaenoides brevibarbis and Coryphaenoides armatus were significantly more abundant at the northern sites; the latter supporting findings using baited landers. The halosaur H. macrochir was the only species affected by slope. The majority of observed fish showed no reaction to one or more of the stimuli produced by the ROV, however burst swimming was observed at least once in all species except B. ferox. The most abundant species, C. brevibarbis, was particularly affected by the presence of the ROV.

Highlights

We report on fishes observed during remotely operated vehicle (ROV) surveys on the Mid-Atlantic Ridge (MAR) undertaken as part of the Ecosystem of the Mid-Atlantic Ridge at the Sub-Polar Front and Charlie-Gibbs Fracture Zone (ECOMAR) project (Priede et al, 2013)
It is possible that some small C. armatus were classified as C. brevibarbis and that some of the rarer Macrourid species were included amongst these two species; Fig. 1
The ROV surveys confirm some of the main conclusions from the baited camera lander surveys on the MAR (Cousins et al, 2013b) showing that the macrourid C. armatus occurs at all stations but with higher abundance in the north compared with south of the CharlieGibbs Fracture Zone (CGFZ)

Summary

Introduction

We report on fishes observed during ROV surveys on the Mid-Atlantic Ridge (MAR) undertaken as part of the Ecosystem of the Mid-Atlantic Ridge at the Sub-Polar Front and Charlie-Gibbs Fracture Zone (ECOMAR) project (Priede et al, 2013). NW and NE, either side of the ridge axis at 2500 m depth north the CharlieGibbs Fracture Zone (CGFZ) and two sites at 491N, SW and SE, at the same depth either side of the ridge axis south of the CGFZ. The aim was to discriminate faunal differences between north and south across a potential latitudinal divide created by the topographic discontinuity of the CGFZ and the presence of the SubPolar Front and North Atlantic Current that traverse the MAR at around 521N (Priede et al, 2013; Miller et al, 2013). Within ECOMAR, three different types of equipment were used to sample demersal fish density and diversity; Semi–Balloon Otter Trawls (OTSB; Cousins et al, 2013a), baited photographic landers

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