Distribution of the biomass-dominant pelagic fish, Bathylagus euryops (Argentiniformes: Microstomatidae), along the northern Mid-Atlantic Ridge

Abstract

The northern Mid-Atlantic Ridge (MAR), from Iceland to the Azores, ranges in depth from 800–4500m and extends over an area of 3.7millionkm2. Despite its size, few studies have described the distribution of pelagic fishes along the MAR. Recent evidence from MAR-ECO, a Census of Marine Life field project, reported increased abundance and biomass of deep-pelagic fishes below 1000m on the ridge, which stands in stark contrast to the traditional view that abundance and biomass decline exponentially with increasing depth in ‘typical’ open ocean ecosystems. Among the midwater fishes sampled during the MAR-ECO campaign, Bathylagus euryops (Argentiniformes: Microstomatidae) was the biomass-dominant pelagic species and ranked third in total abundance. In this paper, we characterize the distribution of B. euryops in relation to physical and biological variables along the MAR. Average catch of B. euryops over the MAR varied between 0.68 individuals/100,000m3±0.70 individuals at the Azorean Zone and 5.82 individuals/100,000m3±2.08 individuals at the Reykjanes Ridge. Generalized linear models applied to B. euryops catch data indicated that ridge section, depth zone, and prey abundance were important explanatory variables in structuring the distribution along the MAR. Analyses of vertical distribution patterns, relative to time of day and fish size, showed that larger fish were found deeper in the water column, likely due to an ontogenetic migration to depth. Mean fish size increased from 58.9mm standard length in the epipelagic zone and continually increased to 155.7mm standard length between 2300–3000m. Due to the high abundance and biomass observed along the MAR, B. euryops appears to be an important species in the oceanic food web of the North Atlantic Ocean.