DOI: 10.5285/f4dfc0ee-4f61-47c5-a5a8-238e02ff2fdd
title: Distribution of mesopelagic fish in the Scotia Sea from RMT25 and pelagic trawls deployed from RRS James Clark Ross and RRS John Biscoe

description: Mesopelagic fish were sampled in the Scotia Sea using a 25 m2 opening and closing rectangular midwater trawl during five research cruises on RRS John Biscoe and RRS James Clark Ross. Nets sampled discrete layers, from the surface to 1000 m during austral spring, summer and autumn. The data include 17726 individual fish records from 66 taxa, the most abundant of which were myctophids of the genera Electrona, Gymnoscopelus, Krefftichthys and Protomyctophum and bathylagids (Bathylagus sp.). Length (standard length, total length or pre-anal fin length) was measured for the majority of specimens (16837), with sex and weight data also collected for many. The work was conducted as part of the BAS Ecosystems Programmes funded by the UK Natural Environment Research Council.
description: Data were obtained from RMT 25 nets deployed from the surface to 1000 m during five research cruises undertaken in the Scotia sea region, including around South Georgia. Cruise JB11 (Piatkowski et al., 1994) was undertaken during January 1991, JR100 was April 2004, with JR161, JR177 and JR200 (Collins et al., 2012) undertaken during austral spring (Nov 2006), summer (Jan 2008) and autumn (March 2009) respectively. During JR100 additional samples were collected with an International Young Gadoid Pelagic Trawl (IYGPT). The RMT25 (see Piatkowski et al., 1994) consists of two nets that are opened and closed on command to sample discrete depth layers. The net was monitored in real-time using a custom-built net monitoring system that logged depth and ambient temperature. Each net had a theoretical mouth opening of 25 m2, with a cod-end mesh of 5 mm and was towed obliquely at 2.5 knots for 30 - 60 min in each depth horizon. The net was fitted with a protected cod-end to keep captured animals in good condition. Nets sampled discrete layers from the surface to 1000 m. Full station details and sampling methods are included in Piatkowski et al. (1994) and Collins et al. (2008, 2012). Net haul catches were sorted to the lowest taxonomic level using published guides (Gon and Heemstra, 1990; Hulley, 1981), and our own reference collection and experience. Species names follow the World Register of Marine Species, but we have used Lampanyctus rather than Nannobrachium for Lampanyctus achirus. Total catch weights were obtained for each fish species using a motion compensated balance. All fish were measured (standard length (SL) and/or total length (TL) to the nearest mm. Each fish can be uniquely identified from a combination of Event - Net - ID. Most of the fish were sampled for stomach contents analysis (Shreeve et al., 2009; Saunders et al., 2015), otoliths and tissue samples were taken for biochemical analyses (Stowasser et al., 2009, 2012) and genetic studies (Van de Putte et al., 2012). Some fish were preserved whole and have been lodged with the Natural History Museum in London.
description: The data are largely consistent with the information published in Collins et al. (2008, 2012) and Piatkowski et al. (1994), but a few points to note: 1. Piatkowski et al. (1994) only included data from Station 1 and Station 2. Data from six additional nets from SW of South Georgia are included here. 2. Collins et al. (2012) only included stratified (non-target) nets, but the data includes fish caught in targeted hauls. 3. There is some uncertainty regarding the specific identification of fish of the genus Bathylagus. Collins et al. (2008) reported B. antarcticus, B. tenuis and B. gracilis, but preliminary molecular analysis (unpublished) suggests that there are four species. It is likely that the fish caught in the southern Scotia Sea are B. antarcticus, but others should be considered Bathylagus sp.