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MARINE FISH
MARINE FISHES OF THE SOUTH-WESTERN NORTH SEA GEN BROAD & JIM R. ELLIS Introduction In order to better understand the status of fish stocks in the North Sea and Atlantic waters, a range of western European nations participate in the International Bottom Trawl Survey (IBTS). These surveys are internationally co-ordinated by the International Council for the Exploration of the Sea (ICES) and have been running in the North Sea since the 1960s (ICES, 2015). These trawl surveys sample a range of bottom-living (demersal) fish and small pelagic fish, with catch information and biological data collected. These surveys provide consistent and standardized data on the species present, their relative abundance and distribution, size composition and, for commercial stocks, information on the age structure and length-at-maturity, and enable the status of the stocks to be monitored over time. The countries participating in the North Sea IBTS include Denmark, France, Germany, Netherlands, Norway, Sweden and the UK (Scotland and England). These data can also provide an important insight into which species occur in the different parts of the North Sea, although it should be noted that trawl surveys only sample a part of the wider fish community, and that trawl survey datasets can contain some erroneous records. The latter may relate to misidentifications of noncommercial species as well as coding errors (Daan, 2001; ICES, 2007; Heessen et al., 2015). This paper summarises the results from the IBTS for those waters around the coast of East Anglia during the period 2016–2020, thus providing some contemporary information on the marine fishes of the area. Methods The International Bottom Trawl Survey (IBTS) of the North Sea samples across the North Sea, including the Skagerrak and parts of the eastern English Channel (ICES, 2015). The gear used is a GOV trawl (chalut à Grande Ouverture Verticale), and the high headline of the trawl allows for small pelagic fish species to be sampled, as well as demersal fish. The trawl is typically towed for 30 minutes duration at predefined sites, the catches sorted and the fish measured (total length) to the cm below (i.e. fish of 240–249 mm are recorded as 24 cm), with herring and sprat measured to the 0.5 cm below. Participating nations upload these data to the DATRAS database, which is hosted by ICES (http://www.ices.dk/data/data-portals/Pages/DATRAS.aspx). The IBTS is conducted twice per year, in the first quarter (Q1) and third quarter (Q3). Data on the numbers-at-length of all fish species captured in the IBTS-Q1 and IBTSQ3 for the years 2016–2020 were extracted (on 13 Oct 2020) for the south-western North Sea (Roundfish Area 5; see ICES, 2015). This area extends from Kent to Lincolnshire, including the coast of East Anglia (Figure 1). The numbers of stations fished in Roundfish Area 5, by year and quarter, are summarised in Table 1. Some processing of those data extracted was undertaken prior to subsequent analyses. Firstly, due to the use of different taxonomic codes, some data nominally reported as genus were mapped to the relevant species. Secondly, data submitted for common smooth-hound Mustelus mustelus were assumed to relate to starry smooth-hound Mustelus asterias (see Farrell et al., 2009). Trans. Suffolk Nat. Soc. 56 (2020)