Pleuronectes platessa, a ghost fish in the Mediterranean Sea?-Pleuronectes platessa, una especie fantasma en el Mediterráneo?

European plaice Pleuronectes platessa often appears in ichthyological check lists for the Mediterranean Sea, as well as in regional field guides and even in some official national landings statistics. However we have not found a single ichthyologist or fisheries biologist who has actually observed this fish in the Mediterranean. The ichthyologic sources available, from classical antiquity to recent times, were checked in order to follow the track of the citations (i.e. true field observations or citations of former authors), and to try to detect misidentifications, if any. Few of these citations appear to be reliable and misidentifications with flounder Platichthys flesus are frequent. Recent scientific trawl surveys have not reported any observations of plaice. The statistics provided by France to the FAO with positive catches of P. platessa appear to be misidentifications of P. flesus. Plaice may have been present in some areas of the Mediterranean in the past, as a result of climatic changes related to the ice age. However, the species seems to be absent now. We propose that this species should be removed from the ichthyofauna records of the Mediterranean.


INTRODUCTION
European plaice Pleuronectes platessa L., 1758 is a very important commercial flatfish in the North Sea. However plaice is almost unknown in the Mediterranean, and the transport and marketing of this species in the area is very rare or absent. Although plaice is normally easily distinguished from related species, such as flounder Platichthys flesus (L., 1758), there can be misidentifications between these species, especially if the nominal identification was based purely on the presence of orange spots (which is not a diagnostic character for plaice).
Since many ichthyologists and fisheries biologists working in the Mediterranean have neither caught nor seen this species in the area, we question its presence in the Mediterranean Sea. In this paper we try to track the path of this fish in the Mediterranean and conclude that it is now absent and may never have occurred in the area.

CLASSICAL ANTIQUITY
According to Thompson (1947) the Greek and Latin classic writers do not mention the plaice. Some flatfish appear in the ancient Greek texts, bouglossa, escaros, rombos, and yhtta, corresponding very clearly to some of the most common flatfish in the Mediterranean: Psetta maxima, Scophthalmus rhombus, Solea solea and other small soleids, and more doubtfully to Bothus podas and Platichthys flesus. The latter species is the only pleuronectid that seems to appear in those ancient writings.
Pliny the Elder mentions "passeres" (IX, 72), likely a pleuronectid, translated as Pleuronectes platessa in several instances (i.e. the French translation edited by Littré, Dubochet 1848, and the English translation published by the Loeb Classical Library in 1983, 2 nd edition, 1 but adding the note "or flounder; the identification is doubtful").
However, the modern translation of several flatfish into Pleuronectes platessa is not well founded on taxonomic work.
Also, in the paintings and mosaics representing fish, few flatfish appear, and the only case we found is the mosaic exhibited in the Sousse Museum (Tunisia) where in the left top of the mosaic a sole-like flatfish occurs. To our knowledge, Pleuronectes platessa does not seem to appear in writings or visual representations during the classical period.
During the period in which Minorca belonged to the English Crown, two publications that included fish lists were published: Cleghorn (1751) did not mention P. platessa or any similar species, and Armstrong (1752) only included English names 3 : Valmont de Bomare (1764) gave the name "grande plie" to P. flesus, present in the coastal lagoons of Montpellier, and "petite plie" or "carrelet" to P. platessa, "characterized by yellow or redish spots".

THE POST-LINNEAN ICHTHYOLOGISTS
Pleuronectes platessa has been cited under a number of synonyms. Some authors include the pre-Linnean synonyms (Delaroche 1809, Günther 1862, others only Linnean names (Norman 1934, Hureau and Monod (eds.) 1973, Eschmeyer 2010. However there are some discrepancies regarding the species identification of the pre-Linnean ichthyologists. In this paper we will only use the name Pleuronectes platessa, regardless of the synonym used by the author.
Some ichthyologists describe P. platessa only for the Atlantic and do not give common names from Mediterranean countries. Among them, Bloch (1801), Lacepède (1802), Bonaparte (1846) and Steindachner (1868). Cuvier and Valenciennes (1828-1849) did not include flatfish in their work. Delaroche (1809) did not find P. platessa in the Balearic Islands but, in addressing Pleuronectes flesus (synonym of Platychtys flesus), he pointed out that the two species have been confused. 4 Risso (1810) cited Pleuronectes platessa as present in the Mediterranean, identified as "P. Plie. Lac. P. Platessa. Lin. (Sollo de Plano)" (sic) giving the reference of Bloch pl. 42, which actually corresponds to Pleuronectes platessa. This is the first and most reliable citation of this species occurring in the Mediterranean.
Weyler (1854) published a list of the fishes of the Balearic Islands, adding Spanish and Catalan names when known. He mentions Pleuronectes platessa, with the Spanish name ("platija") but no common name in Catalan. Graells (1864) attributed the Catalán name "palaya" to Pleuronectes platessa although he did not specifically mention its occurrence in the Mediterranean. That name (with obsolete spelling) is a generic name for many flatfish ("palaia") in the geographical area with Catalan as a main language. Doûmet (1869) mentioned "la plie" (Platessa passer) as the only pleuronectid species occurring in the brackish waters along the Languedoc coast. According to Bonaparte (1846), Platessa passer corresponds to the species Platichthys flesus and the French name should be "flet". However, in a previous paper (Doûmet, 1860) this author had presented Platessa passer under the common Occitan name "plana" which corresponds to P. flesus, while the word "plie" is not mentioned at all. Barceló (1868) listed Pleuronectes platessa in his list without a common Catalan name, but he mentioned that the citation was based on Weyler (1854) and that he had never seen any specimens. Steindachner (1868) questioned the presence of the species in the waters of the Southern Spanish Atlantic, as cited by Machado (1857), and suggested that it was based on misidentifications of Platichthys flesus, which did not appear in his list. 5 The confusion between these two pleuronectid species could have been a recurrent problem in the Mediterranean. Moreau (1881) cited P. platessa as present in the Atlantic Ocean but not for the Mediterranean Sea. Faber (1883) cited P. platessa in the Adriatic on the basis of two specimens bought at the market in Venice. 6 Navarrete (1899) considered that P. platessa was "more common in our Atlantic than in the Mediterra-nean, where [it] is almost rare". 7 In a table he added the same common Catalan name given by Graells (1864). In the bibliography he referred to the accounts of Graells (1864), Cisternas (1867) and Barceló (1868). Pérez Arcas (1923) 8 also took the citation and Catalan name from Graells (1864) . De Buen (1926) reported the species for the Balearic Islands without a local name, and it is likely that he took the citation from Barceló (1868). Fage (1907) collated all the fish listed by the previous authors, including Graells (1864) and Barceló (1868), and P. platessa was included in his catalogue. Norman (1934) provided one of the most reliable notices that Pleuronectes platessa can occur in the northern Adriatic Sea. A specimen was reported for Trieste (the same as cited by Faber, 1883) and another, with a question mark, for Naples. 9 De Buen (1935) reported P. platessa as occurring in the Balearic Islands, on the basis of his previous account (De Buen 1926) but now without details of the sources he used. Padoa (1931Padoa ( -1956 listed Pleuronectes platessa, but using only Atlantic references and he stated explicitly that it was extreme rare in the Mediterranean and absent from Italian waters. 10 Lozano Rey (1960) did not report Pleuronectes platessa from the Mediterranean and, although he did report a specimen bought in Valencia market, he made it clear that it originated from the Bay of Biscay. 11 Bini (1965Bini ( , 1968 reported the occurrence of Pleuronectes platessa in the Mediterranean, but admitted that it was extremely rare. 12 The CLOFNAM (Hureau and Monod (eds.) 1973), noted the presence of P. platessa in the Black Sea, but without reference. There is no other document reporting the occurrence of this species in that area. 7 "Más común en nuestro Atlántico que en el Mediterráneo, donde es casi rara." 8 Actually finished in 1865, but published in 1923 by Lozano Rey. 9 "The occurrence of the Plaice in the Adriatic is difficult to credit and requires confirmation. In 1878, Trois found two specimens in the fish-market at Venice, and the only other record of the species being found in this region is the statement by Jordan and Goss (1889) that they had examined examples from Trieste (Coll. Salmin). One of these specimens has been sent to the British Museum by the Museum of Comparative Zoölogy, through the courtesy of Prof. T. Barbour, and proves to be a typical Pleuronectes platessa" 10 "Specie in Mediterraneo rarissima, e nelle acque italiane probabilemente assente. Ci limiteremo ad accennare brevemente as suo sviluppo, ormai ben consciuto grazie alle ricerche che numerosi AA. hanno condotto sulle coste Occidentali Europee, dove questa specie è abontantissima ed economicamente molto importante." 11 "La especie es propia de las costas septentrionales y occidentales de Europa, hasta el estrecho de Gibraltar, existiendo también en el Mediterráneo occidental, aunque no parece que sea muy abundante en este mar. (...) En nuestra colección de estudio hay [un ejemplar] que adquirimos en el mercado de Valencia, pero procedente de un puerto cantábrico." 12 Bini (1968) writes "In Italia assolutamente occasionale" and "E' stata trovata anche nel Mediterraneo alle Baleari e sembra a Napoli e nell'alto Adriatico. E' molto dubbia però la presenza nelle nostre acque e in ogni caso estremamente rara". Tortonese (1975) is quite clear regarding the presence of Pleuronectes platessa in the Mediterranean. He believed that the nominal records were more likely due to confusions with Platichthys flesus or based on specimens seen in the markets than an actual presence in the Mediterranean. 13 Only authors mentioning or discussing the occurrence of Pleuronectes platessa in the Mediterranean are presented above. However, there are many other authors who in their lists and catalogues do not cite this species. Table 1 lists those bibliographic references including and excluding Pleuronectes platessa in the Mediterranean.

THE GUIDES
Two very prestigious guides suggest the presence of Pleuronectes platessa in the Mediterranean. Nielsen (1986) gave a distribution area continuously covering the whole Spanish and French coast line and the Italian Ligurian and Tyrrhenian Seas, as far as the Messina Straits. Fischer et al. (1987) gave its distribution area as covering the whole Spanish coast, with an uncertain distribution (indicated with a dotted line) along the French coast and the northern part of the Italian Adriatic Sea. The presence of Pleuronectes platessa is pointed out by some other general or local lists, popular guides and field guides, but some others do not mention this species at all. For an extended record of these references see Table 1.

SCIENTIFIC TRAWL SURVEYS
A number of scientific trawl surveys have been carried out in the Mediterranean. MEDITS is a systematic demersal trawl survey undertaken by the European countries since 1994. According to Désaunay et al. (2006), plaice has never been caught during bottomtrawl surveys in recent years along the northwestern Mediterranean in the MEDITS cruises. After 30 years of sampling in the northern and Central Adriatic (including cruises targeting flatfish with a specific gear) not one specimen of Pleuronectes platessa has been seen or cited (Giovanardi, com. pers.). According to Piccinetti (com. pers.), the only peluronectid species present in the Adriatic Sea is Platichthys flesus. Crespo et al. (2001) published the vernacular names used in the fish auctions in Spain. They did 13 "è molto dubbia l'esistenza di P. platessa, nei cui riguardi non possediamo che scarse notizie, vecchie e malsicure. Carus (1893) la cita per la Sicilia, Venezia e Trieste, Fage (1907) per le isole Baleari. Non si può escludere che questa notissima specie del1'Atlantico settentrionale penetri anche nelle acque mediterranee, ma assai maggiore è la probabilità che in passato vi siano state confusioni fra P. platessa e P. flesus o che si siano visti sui mercati individui di provenienza atlantica." not report Pleuronectes platessa for any Mediterranean harbour. In a further edition (Crespo and Ponce 2003), Pleuronectes platessa appears with vernacular names for Catalonia, but it seems that for this edition the authors included names from bibliographic sources.  1926De Buen 1934Norman 1935De Buen 1965Bini 1968Bini 1968Luther and Fiedler 1984Campbell 1986Nielsen 1987Fischer et al. 1987 1903Ferrer Hernández 1904Sánchez Comendador 1905Calvet 1906Ferrer Aledo 1913Gibert 1916Boscà 1920 Borja y Goyeneche** 1921 Pruvot 1921Pardo 1931-1956Padoa* 1960Lozano Rey* and ** 1961Palombi and Santarelli 1975Tortonese 1979Centelles 1981Nadal* 1986Riedl 2006 Probably a mistake in the common name. ‡ Not clear, since it uses the English nomenclature. & Implicit citation of Pleuronectes platessa by giving a name in Catalan (a language only present in the Mediterranean). * Explicit citation of Pleuronectes platessa as an absent species or not seen caught in the Mediterranean. ** Cited only for the Atlantic. A test on the species naming system in the "criée" of Sète was conducted, requesting that any specimen of "plie" (which contributes to the nominal statistics) observed in the landings be saved. Several fishermen and scientific observers conducting regular samplings of the landings in the Gulf of Lions were also approached. On all the occasions, ten visits involving about 30 specimens, those named "plie" were actually "flet", and no confirmed observations of true "plie" were made. Specimens of "flet" are named "plie" also in Marseille and Grau du Roi. Furthermore, we were informed that "plie" occurs in the lagoons along the French coast, and this estuarine habitat would be the normal environment where Platichthys flesus (the "flet") would be expected to occur.

GEOGRAPHICAL DISTRIBUTION AND CLIMATE CHANGE
Pleuronectes platessa is a boreal species, and its occurrence in the Mediterranean Sea seems doubtful. However, the cold period known as the Little Ice Age (LIA), could have played some role in the changes of its geographical distribution. It is likely that the species was not present in the Mediterranean during the long warm period embracing the ancient (classical) and medieval ages. However, during the LIA (roughly 1500-1850), its distribution range may have expanded further to the south, and it could have entered through the Straits of Gibraltar following the northern shelves of the Mediterranean. At the end of the LIA, relict populations may have persisted in the cooler parts of the region (e.g. the Gulf of Lions and the northern Adriatic). Thus, the occurrences reported by Risso (1810) and Norman (1934) could correspond to actual specimens of P. platessa taken from declining populations before their disappearance.

CONCLUSION
It seems that the classical authors do not mention Pleuronectes platessa at all, but probably referred to Platichthys flesus, and some translations have clearly confused the two species. The renaissance ichthyologists identified P. platessa, but never explicitly as occurring in the Mediterranean. The most prestigious ichthyologists to cite Pleuronectes platessa in the Mediterranean are Risso (1810), De Buen (1926, 1935, Norman (1934), Nielsen (1986) and Fischer et al. (1987). Although other authors (Weyler 1854, Graells 1864) mention Pleuronectes platessa in Spanish publications, these authors are not eminent ichthyologists and their reports are doubtful. As Tortonese (1975) suggested, some nominal accounts may have been based on misidentified Platichthys flesus. Other authors (e.g. Barceló, 1868;Navarrete, 1898) have simply reiterated these accounts. This may also be true for the 20 th -century Mediterranean guides, including Nielsen (1986) and Fischer et al. (1987). In Table 1, the most significant publications of the Mediterranean fish fauna are classified according to the presence/absence of Pleuronectes platessa.
It cannot be shown that Pleuronectes platessa has never occurred, and it may indeed have occurred in the past in the cooler waters of the Mediterranean (northwestern basin and northern Adriatic) as a response to changing environmental conditions. However, it seems that in recent years this species has not been present. Several authors have explicitly remarked on its absence in the Spanish Mediterranean (Nadal 1981, Duran 2009), and others claim that they have not seen this species in the same area (Delaroche 1809, Lozano Rey 1960.
As a conclusion we propose removing Pleuronectes platessa from the ichthyofaunal lists for the Mediterranean. Even if it was present in the past, which is possible but doubtful, there is no recent scientific evidence to confirm the presence of this species in the Mediterranean. Consequently, on-line guides and catalogues, as well as landing statistics, should be corrected accordingly.

AKNOWLEDGEMENTS
We have asked many ichthyologists and fisheries biologists if they have really seen this species in the Mediterranean. We thank in particular Prof. J.P. Quignard and Dr. P. Olivar for providing bibliographic material, Prof. C. Piccinetti and O. Giovanardi for the information on the Adriatic fauna, C. Karlou-Riga and her colleagues for the information on the eastern Mediterranean, and the "criée" of Sète and the "Eclipse" group of observers for their help on providing specimens. We also are grateful to the following researchers, who confirmed they have never seen any specimens of Pleuronectes platessa caught in the western Mediterranean: P. Abelló, R. Allué, E. Azzurro, C. Bas, J. Camp, J.B. Company, M. Demestre, D. Lloris, A. Lombarte, P. Martín, E. Massutí, L. Recasens, A. Sabatés, P. Sánchez, F. Sardà.