Occurrence of Blue-Mouth Redfish Helicolenus Dactylopterus in the southern North Sea – Jim Ellis

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OCCURRENCE OF BLUE-MOUTH REDFISH HELICOLENUS DACTYLOPTERUS IN THE SOUTHERN NORTH SEA JIM ELLIS

J. Ellis

Blue-mouth redfish, also known as blackbelly rosefish, Helicolenus dactylopterus (Delaroche, 1809) (Suborder Scorpaenoidei; Family Sebastidae) is a small-bodied demersal fish that attains a maximum size of 44–51 cm total length (LT), but is usually <30 cm LT (Hureau & Litvinenko, 1986; Heessen & Blasdale, 2015). It is distributed widely in the Atlantic Ocean and, within the North-east Atlantic, is found from Scandinavia to Morocco, including the Mediterranean Sea, where it is most common in waters of 200–800 m depth (Hureau & Litvinenko, 1986). Around the British Isles, blue-mouth redfish occurs predominantly along the edge of the continental shelf from the Celtic Sea to Northern Scotland but is usually absent or infrequent from shallower sea areas (Heessen & Blasdale, 2015). Although it occurs primarily in deeper waters to the west of the British Isles, there can be periodic influxes of young fish into the northern North Sea, with these events resulting in blue-mouth redfish becoming more dispersed in the North Sea, including the central and southern areas, in subsequent years (Heessen et al., 1996).

There are limited records of this species from around the coast of East Anglia, and it was not reported by Paget & Paget (1834) in their initial ichthyofaunal list for Great Yarmouth. Patterson (1910) reported on three specimens (as American rose perch Scorpaena dactyloptera; one specimen of 14.6 cm (5¾ inches) length caught by shrimp trawl in April 1894, a second specimen (20.3 cm; 8 inches) landed at Lowestoft in December 1895 and a third specimen landed at Lowestoft in March 1909), with the two latter records also detailed in Collings’ (1933) list of the fishes of Suffolk. Whilst blue-mouth redfish has been recorded occasionally from the areas just north of East

Figure 1. Specimen of blue-mouth redfish Helicolenus dactylopterus caught in the southern North Sea, showing (a) whole specimen (148 mm LT) and (b) inside of mouth.

Trans. Suffolk Nat. Soc. 57 (2021)

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Suffolk Natural History, Vol. 57

Anglia (Broad & Ellis, 2020), their occurrence from the waters of southern Suffolk, Essex and the Outer Thames is more sporadic. Indeed, this species was not reported in the accounts of Laver (1898), Murie (1903), Wheeler (1979) or Attrill (1998).

Helicolenus dactylopterus is distinguished from related species of redfish (Sebastes spp.) that occur in the North Sea by the dark-coloured interior of the mouth, a dorsal fin with <14 spines (cf. 14–16 spines in Sebastes) and an anal fin with five soft rays (cf. six of more in Sebastes).

On 22 July 2021, during an annual trawl survey of the North Sea, a specimen of H. dactylopterus (Fig. 1) was captured at a sampling site in the southern North Sea (shot position: 51° 44.2’ N, 01°, 44.75’ E; 31 m depth; haul position: 51° 45.74’ N, 01°, 46.7’ E; 28 m depth). The fresh specimen was 15 cm LT and weighed 48 g, although subsequent examination of the specimen (after freezing and thawing) indicated it was 14.8 cm LT ). The dorsal fin had 12 spines and 13 soft rays, the anal fin had 3 spines and 5 soft rays. These meristic characters were in the expected range for H. dactyllopterus (D: 12 (11–13) + 10–14; A: 3 + 5; Hureau & Litvinenko, 1986). The specimen featured the normal rosy colouration of the species, with some darker bands, and the dark-coloured interior to the mouth (Fig. 1) is also a characteristic feature. This is one of the more southerly records of H. dactylopterus in the North Sea. Data from the International Bottom Trawl Survey (IBTS) held on the ICES database of trawl survey data (DATRAS; https://www.ices.dk/data/dataset-collections/Pages/ Fish-trawl-survey.aspx; downloaded 18/08/2021) indicate that there has been a recent increase in the catch rates of H. dactylopterus since 2017, as indicated by data from the survey undertaken in the first quarter of the year (IBTS-Q1; Fig. 2). Data from the survey undertaken in the third quarter (IBTS-Q3) provide further confirmation of

Figure 2. Average catch rates (numbers per hour) of blue-mouth redfish Helicolenus dactylopterus in the Quarter 1 North Sea IBTS (round fish areas 1–7 only) over the period 2000–2021. See ICES (2015) for a further description of the survey.

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BLUE-MOUTH REDFISH IN THE SOUTHERN NORTH SEA

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this recent influx of H. dactylopterus. Preliminary examination of the underlying data for IBTS-Q3, however, were suggestive of potential misidentifications between H. dactylopterus and Sebastes spp., and there were also some very high catches that could usefully be checked and verified prior to further analysis. Consequently, data from the Q3 survey are not shown here. More detailed investigations of the latest ‘invasion of the North Sea’ by blue-mouth redfish, including comparison with the studies relating to the previous influx of the species from the 1990/1991 recruitment event, as described by Heessen et al. (1996), could also usefully be undertaken in the coming years.

Acknowledgements Thanks to CEFAS colleagues for retaining the specimen. This study also used data from the ICES North Sea International Bottom Trawl Survey, with these institutes thanked for their contributions to this internationally-coordinated survey.

References Attrill, M. J. (1998). A rehabilitated estuarine ecosystem: The environment and ecology of the Thames Estuary. Dordrecht: Kluwer Academic Publishers, 267 pp.

Broad, G. & Ellis, J. R. (2020). Marine fishes of the south-western North Sea. Trans.

Suffolk Nat. Soc., 56: 37–50.

Collings, D. W. (1933). The fishes of Suffolk. Trans. Suffolk Nat. Soc., 2: 104–133.

Heessen, H. J. L. & Blasdale, T. (2015). Scorpaenidae. In Fish atlas of the Celtic Sea, North Sea, and Baltic Sea (Heessen, H. J. L., Daan, N. and Ellis, J. R., Eds.).

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Heessen, H. J., Hislop, J. R. & Boon, T. W. (1996). An invasion of the North Sea by bluemouth, Helicolenus dactylopterus (Pisces, Scorpaenidae). ICES Journal of Marine Science, 53: 874–877.

Hureau, J.-C. & Litvinenko, N. I. (1986). Scorpaenidae. In Fishes of the North-eastern Atlantic and the Mediterranean (Whitehead, P. J. P., Bauchot, M.-L., Hureau, J.-C., Nielsen, J. & Tortonese, E., Eds.). Paris: UNESCO, 1211–1229.

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Laver, H. (1898). The mammals, reptiles and fishes of Essex. Essex Field Club Special Memoirs, 3: 138 pp.

Murie, J. (1903). Report on the sea fisheries and fishing industries on the Thames Estuary. Kent and Essex Sea Fisheries Committee. London: Waterlow Bros. & Layton, 250 pp.

Paget, C. J. & Paget, J. (1834). Sketch of the natural history of Yarmouth and its neighbourhood. London: Longman, Rees & Co., xxxii + 88 pp.

Patterson, A. H. (1910). Rough notes on the fish and fisheries of East Suffolk. Great Yarmouth: John Buckle.

Wheeler, A. C. (1979). The tidal Thames: the history of a river and its fishes. London: Routledge & Kegan Paul Books, 228 pp.

J. R. Ellis, CEFAS, Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk NR33 0HT

Trans. Suffolk Nat. Soc. 57 (2021)