Occurrence of the kuruma prawn Marsupenaeus japonicus ( Spence Bate , 1888 ) in the Celtic Sea , English Channel , and North-West France

The most northern occurrence in European waters of the Japanese or kuruma prawn Marsupenaeus (Penaeus) japonicus Bate, 1888 is reported from the Celtic Sea. Two specimens were captured during the winter and spring of 2007 from depths ~40 to 60m over mobile sediments by trawling. Other northern European records are reviewed.


Introduction
Marsupenaeus japonicus (Spence Bate, 1888) is a commercially important penaeid with a native range encompassing the Indo-West Pacific from the Red Sea, E and SE Africa to Korea, Japan, and the Malay Archipelago, and it has also been reported from Fiji (Holthuis 1980).The species is thought to have invaded the eastern Mediterranean through the Suez Canal during the 1920s and since has spread successively along the Levantine coast (Egypt, Israel, Lebanon, Syria, and Turkey) to Greece (Rhodes) and Cyprus (Galil et al. 2002).Indeed, d'Udekem (1999) reported that M. japonicus has almost excluded the previously commercially-important native penaeid prawn Melicertus kerathurus (Forskål, 1775) from the easternmost part of the Mediterranean.
The kuruma prawn has been farmed in Japan since the late 1950s (Honma 1980) and, during the 1980s, M. japonicus was introduced to a number of European countries (Italy, France, Spain and Portugal) for pond aquaculture (http://www.fao.org/fishery/introsp/search/en).It is now successfully cultivated in the Central and Western Mediterranean (Galil and Zenetos 2002;Streftaris et al. 2005), and there is some cultivation along the French Atlantic coast (Quero and Vayne 1998); previously as far north as Brest (IFREMER Hatchery, Argenton, NW Brittany; 48.5167 0 N, 04.7417 0 W) and the Cherbourg Peninsula (SATMAR Hatchery, Barfleur, Normandy; 49.6711 0 N, 01.2633 0 W) (Clark 1990a, b).The species is currently farmed semiextensively in coastal brackish-water lagoons in the Marennes-Oleron (45.9536 0 N, 01.2497 0 W) area (near La Rochelle) and marginally near Guerande, S Brittany (47.3281 0 N, 02.4333 0 W).Prawn larvae are obtained from hatcheries located in the Gironde Estuary (Le Petite Canau, Le Port de Saint-Vivien (45.4320 0 N, 01.0360 0 W), near Bordeaux and Spain (Andalusia), and reared from May to October to a market weight of 20-40 g.Total French production is ~30 tonnes per year.Occasional captures in the Bay of Biscay (Mazurie 2005) [Figure 1] have been attributed to escapees from these French farms (N.Ranninger, Bord Iascaigh Mhara -BIM, Paris, France pers.comm.).
The first specimen represented the first known record from Irish waters and the second a northward extension of ~120 km in the NE Atlantic.Both specimens have been deposited in the National Museum of Ireland, Dublin (NMI NH 2007.45 andNMI NH 2009.15).

Discussion
Marsupenaeus japonicus has been recorded on at least 15 occasions from UK, Irish, and NW French Atlantic waters over the last twenty years (Appendix 1, Figure 2); with most (N=12) from the western approaches of the English Channel reported during the last two decades (~57% were recorded during 2007 alone).It is interesting that ~73% (N=11) of the specimens were recorded during the first half of the year (January to June inclusive) and it may mean that M. japonicus is more vulnerable to capture during periods of lower water temperatures due to inactivity, perhaps during hibernation, and/or their daytime burrowing behaviour (Abe et al. 2007).
It has been suggested that the M. japonicus found in UK waters may have escaped from one or more French farms (Clark 1990a, b).This may also be the case for the two records reported here.Attempts at rearing several species of penaeid prawns (including M. japonicus) within enclosed warm-water recirculation units were carried out at Conwy (53.2829 0 N, 03.8295 0 W), North Wales during the 1970s (Forster and Wickins 1972;Forster and Beard 1974;Walne 1977;Wickins and Beard 1978;Lee and Wickins 1992).However, these trials were terminated in l980 (Ian Laing pers.comm.) and could not be considered responsible for the findings since 1989 and 1990 given that the life-span of M. japonicas is approximately 2.5 years in the Mediterranean (Tom and Lewinsohn 1983;Galil et al. 2002).Marsupenaeus japonicus larvae require water temperatures above 24ºC; the rate of growth increases with temperature to 32ºC, the optimum being 28-30ºC (Galil 2006;Hewitt and Duncan 2001).However, adults can tolerate water temperatures down to 10ºC (Lucas and Southgate 2003).Salinities below 27 and above 35 inhibit hatching and induce high mortalities.However, adults are poor osmoregulators compared with the young, preferring salinity > 35 (Galil 2006).Considering their thermal and salinity preferences, it seems more likely that the Irish and UK specimens were derived from the immigration of benthic juveniles and/or adults from southern latitudes rather than by the northward dispersal of free-swimming larvalstages.Increasing sea water temperatures in the area during recent decades (Boelens et al. 2005) may have facilitated their survival.
Although some of the Irish and UK specimens were relatively large (mean TL 185 mm; range 80-240 mm; N=9), there is currently no indication of natural reproduction at this northern edge of its range.Females mature at >140 mm TL and reproduce from April to November in the south-eastern coast of the Mediterranean (Tom and Lewinsohn 1983).According to Holthuis (1980) the maximum TL (and CL) for males and females is 190 mm (53mm) and 225 mm (66mm), respectively.
All of the specimens recorded to date have been captured in demersal gear, including beam trawls (6), otter trawls (3), Nephrops trawls (2), prawn pots (2), and shrimp nets (1) at depths of 1 to 90 m (mean depth 54 m; N=7).According to Galil et al. (2002) and Holthuis (1980), M. japonicus is usually found on sandy, or sandy-mud bottoms at depths of 0-90 m, usually <50 m.Although Tom and Lewinsohn (1983) discovered that M. japonicus migrate from inshore waters to the open sea during their benthic life cycle on the south-eastern coast of the Mediterranean Sea, no apparent difference was noted in the seasonal distribution of records in the current study (Figure 2).The two potcaptured specimens (record numbers 6 and 13), both taken during September, are likely to have been actively feeding.Further records may be expected.

Figure 2 .
Figure 2. Distribution of Japanese or kuruma prawn Marsupenaeus (Penaeus) japonicus records in the Celtic Sea, English Channel and NW France.Specimens captured during the first half of the year (January -June) are indicated by blue circles while specimens captured during the second half of the year (July -December) are indicated by red circles.The location of French kuruma prawn hatcheries are indicated by green triangles.