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First record of Montagu’s sea snail Liparis montagui (Donovan, 1804) in Belgian waters

Montagu’s sea snail Liparis montagui (Donovan, 1804) is a demersal fish species from the Liparidae family, occurring in the inshore waters of the North East Atlantic. It is found around southern Iceland and from the Barents Sea southwards through the North Sea and the Baltic Sea and along European coasts. young specimens are also found in the wadden Sea (1, 2, 3, 4). L. montagui occurs from the intertidal to 30 m, under stones at low tide, in rock pools or clinging to algae (e.g., Fucus). It feeds primarily on gammarid amphipods in intertidal areas and shrimps and small crabs in subtidal areas (2, 3, 5, 6).

Montagu's sea snail Liparis montagui (Donovan, 1804) is a demersal fish species from the Liparidae family, occurring in the inshore waters of the North East Atlantic. It is found around southern Iceland and from the Barents Sea southwards through the North Sea and the Baltic Sea and along European coasts. young specimens are also found in the wadden Sea (1,2,3,4). L. montagui occurs from the intertidal to 30 m, under stones at low tide, in rock pools or clinging to algae (e.g., Fucus). It feeds primarily on gammarid amphipods in intertidal areas and shrimps and small crabs in subtidal areas (2, 3, 5, 6).
A specimen of L. montagui was found on March 9 th , 2011 at sampling location ft330 (N51.433, E2.815 -N51.427, E2.794) on the Gootebank at a depth of 23 m (Fig. 1). The sample was taken with an 8 meter-shrimp beam trawl (stretched mesh width 22 mm in the cod end) dragged over the bottom for 15 minutes at an average speed of 4 knots. The 40 l catch contained some larger stones, and dab Limanda limanda and whiting Merlangius merlangus as the most abundant fish species. Montagu's sea snail Liparis montagui is very similar in appearance and habits to the sea snail L. liparis. The pelvic fins of both species are modified into a suction disc on the belly and both are variably coloured. Still, a number of characteristics make it possible to distinguish the two species. L. montagui is purplish brown in appearance to the naked eye, but with the assistance of a lens one can see that the groundcolour is yellowish brown with dark spots. L. liparis on the other hand tends to be pale grey or brown, with darker brown or purplish longitudinal bands (6, 7). L. montagui can further be distinguished from L. liparis by its smaller size (max. 12 cm versus 18 cm), the never overlapping dorsal and caudal fins, the rarely overlapping anal and caudal fins, the smaller number of rays in the dorsal (26-32 versus 32-45) and anal fins (22-26 versus 26-38) and the posterior nostrils in adults that are covered by skin (3,5,6,8,9,10).
Since fin ray counts provide the most reliable distinction between the two species (11), we particularly focused on this characteristic. Table  1 gives an overview of the literature concerning the number of dorsal and anal fin rays in both species. Table 2 presents the identification characteristics of the found specimen and a L. liparis specimen caught at another location in the Belgian part of the North Sea, compared to the minima and maxima found in literature. The photograph (Fig. 2) and drawing (Fig. 3) of the found specimen clearly show that neither the dorsal nor the anal fins overlap with the caudal. Also, the fin ray counts of the anal and dorsal fins of the found specimen clearly correspond with the characteristics of L. montagui. we can conclude that this is the first unequivocal evidence of a recording of L. montagui in the Belgian part of the North Sea.  Table 2 Examined identification characteristics compared with literature.
during our long-term monitoring programs, regular beam trawl samples have been taken for over 20 years on the Belgian part of the North Sea. These data showed that L. liparis is a common species throughout the area (4) while L. montagui was never observed (pers. obs.). There was uncertainty about the possible observation of L. montagui during a sampling campaign on September 24 th , 2007 (4 years prior to the reported observation), but unfortunately due to the inferior condition of the specimen we were unable to make a straightforward identification. Hence, the recording of March 9 th , 2011 is considered to be the first official reported catch of L. montagui for the Belgian marine waters. Since then, L. montagui has been reported from Belgian waters by Hans De Blauwe (12) at the marina of Zeebrugge and by Kelle Moreau (pers. comm.) at the coastal zone of Nieuwpoort, the latter caught on September 9 th , 2013 from R.V. Simon Stevin with a 6 meter shrimp beam trawl and a similar small mesh net. In both cases, the specimen was not preserved and the identification could not be confirmed. However, these observations may indicate that L. montagui has established a resident population along the Belgian coast. L. montagui has been reliably reported in the UK (13). Also Wheeler (14) has examined specimens from various parts of the coasts of England, wales and the Isle of Man. In the North of France (Nord-Pas-de Calais), the species was inventoried by Glaçon in the 1970s, and it was identified in the updated inventory of Müller (2004) as a common species for this region (15,16). In the Netherlands, L. montagui is considered a very rare species and its protection status is covered by national and international legislation (17,18).
we can assume that L. montagui has been present in the Belgian part of the North Sea for some time already, but probably in very low  numbers. The small population, small size and limited distribution make it difficult to capture representatives of this species (13). The fact that our monitoring program normally covers soft sandy sediments, and L. montagui is a typical species of rocky sediments, contributes to this. Although location ft330 has always been a 'stony' habitat, L. montagui was not previously caught in this area. Perhaps climate change has favoured the appearance of this species in Belgian waters in recent years. Also, the recent introduction of wind farms (and hard substrates) in the vicinity of this area may act as an attraction pole for L. montagui.
Increased monitoring efforts will probably reveal more species that are new to the Belgian fauna in the future. For now, we have shown that Montagu's sea snail L. montagui is indeed present in the Belgian part of the North Sea.

AcKNOwLEDgEMENTS
Shiptime on board of R.V. Belgica was provided by BELSPO through RBINS. Sampling was part of the long-term monitoring program carried out by ILVO in the framework of aggregate extraction, dredge disposal and offshore wind energy.