short scientific article	UDC 591.9:597.3 (262.5)
received: 2005-01-06
PONTIC OCCURRENCE OF THE BLUNTNOSE SIXGILL SHARK, HEXANCHUS GRISEUS (BONNATERRE, 1788) (CHONDRICHTHYES: HEXANCHIDAE)
Hakan KABASAKAL
Ichthyological Research Society, Ataturk mahallesi, Mentejoglu caddesi, idil apt., No: 30/4, Umraniye, TR-34764 istanbul, Turkey
E-mail: hakankabasakal@hotmai l .com
ABSTRACT
On 19 November 2004, one male specimen of Hexanchus griseus of 300 cm TOT and weighing 250 kg was captured by a commercial gill-netter nearly 3 miles off the coast of Amasra (SW Black Sea, western Anatolian coast). This single capture extends the Mediterranean distribution of H. griseus to the Black Sea and confirms its pontic occurrence.
Key words: Hexanchus griseus, sixgill shark, hexanchidae, Black Sea, distribution
PRESENZA PONTICA Dl SQUALO CAPOPIATTO HEXANCHUS GRISEUS (BONNATERRE, 1788) (CHONDRICHTHYES: HEXANCHIDAE)
SINTESI
Il 19 novembre 2004 un esemplare maschio di Hexanchus griseus, di 300 cm di TOT e 250 kg di peso, è stato catturato con una rete commerciale per piccoli pesci cartilaginei, tre miglia al largo della costa di Amasra (Mar Nero sud-occidentale, costa anatolica occidentale). Questa singola cattura estende al Mar Nero la distribuzione mediterranea di H. griseus e conferma la sua presenza pontica.
Parole chiave: Hexanchus griseus, squalo capopiatto, Hexanchidae, Mar Nero, distribuzione
INTRODUCTION
Hexanchus griseus (Bonnaterre, 1788) is a wide ranging species in temperate and tropical seas, including Mediterranean and adjacent waters, living at depths from the surface to at least 1875 m (Boeseman, 1984; Com-pagno, 1984; Bauchot, 1987; Capape et a/, 2003). Occurrence of the bluntnose sixgill shark in the Black Sea has always been a point of discussion. In a very old and questionable record by Geldiay (1969, in Bilecenoglu et a/., 2002), the author reported on the presence of H. griseus from the Black Sea, without giving any information on the fishing locality of the examined specimen, or the name of the institution, where the specimen is preserved for further inspection. Due to the lack of adequate information, Bilecenoglu et a/. (2002) considered this pontic recording of H. griseus by Geldiay (1969) as 'questionable' and requiring confirmation. In the monumental works by Slastenenko (1956) and Ak§iray (1987), the authors did not report on the presence of bluntnose sixgill shark from the Black Sea. In a recent study by Kabasakal (2004), the author reported on a capture of a single specimen of H. griseus in the prebos-phoric Black Sea waters, where their physical conditions are practically under the influence of the Marmaric current. Because of this reason, Kabasakal (2004) emphasized the necessity of further research in order to reveal whether the pontic distribution of H. griseus extends throughout the entire Black Sea.
In this short communication paper, new data on the capture of a bluntnose sixgill shark off the Anatolian coast of the southwestern Black Sea is presented and its pontic distribution discussed.
MATERIAL AND METHODS
Fig. 1: Male specimen of Hexanchus griseus of 300 cm TOT and weighing 250 kg, captured off the coast of Amasra (SW Black Sea).
Sl. 1: Samec šesteroškrgarja Hexanchus griseus, 300 cm celotne iztegnjene dolžine in težak 250 kg, ujet v mrežo slabe 3 milje od obale Amasre (fZ Črno morje).
RESULTS AND DISCUSSION
On 19 November 2004, one male specimen of Hexanchus griseus of 300 cm TOT and weighing 250 kg (Fig. 1) was captured by a commercial gill-netter nearly 3 miles off the coast of Amasra (SW Black Sea, western Anatolian coast; Fig. 2). On the photograph taken of the specimen (Fig. 1), 6 gill slits are clearly visible on the left side of the head, which enabled the author to identify the captured specimen as H. griseus. Unfortunately, as the sixgill shark was immediately eviscerated and sold at a local fish market, no biometrical measurements of this pontic specimen could be made.
This study is part of an extensive ongoing research, which was launched in 2002, in order to investigate the distribution of Hexanchus griseus in Turkish waters. Data have been collected from the following sources: 1) fishing logs of commercial vessels; 2) records of local fish markets; 3) field surveys; and 4) notes appearing in daily newspapers, fishing magazines, etc. The author was informed about the capture of a specimen of H. griseus off the coast of Amasra (SW Black Sea) on 19 November 2004, after reading an article in a local newspaper. Although the sixgill shark was immediately eviscerated and sold at a local fish market, the fisherman provided a photograph of the captured specimen taken from its left side. Identification of this specimen was made on the basis of this photograph, now kept in the author's personal archive. The species identification follows Compagno (1984). Total length (TOT) and weight data were provided by the fisherman.
Fig. 2: Map showing the capture localities of prebos-phoric (•) and Amasra specimens (▲) of H. griseus. Sl. 2: Zemljevid z lokalitetami ujetih predbosporskih primerkov vrste H. griseus (•) in primerka, ujetega v bližini Amasre (▲).
Although, H. griseus can penetrate to shallow areas and even rise to surface waters, particularly at night (Boeseman, 1984; Dunbrack & Zielinski, 2003), it normally inhabits deep water over the continental shelf and upper slope to at least 1875 m (Compagno, 1984). Regarding the chemical properties of sea water in bathyal zone of the Black Sea, the water column below 200 meter is contaminated with hydrogen sulphur (Prodanov et a!., 1997), a toxic substance which kills any marine organism depending aerobic conditions. Therefore, it is possible to suppose that in the Black Sea, bluntnose six-gill shark can not survive at depths below 200 metres
due to the anaerobic conditions prevailing in the bathyal pontic waters. This circumstance seems to be a critical factor, which can restrict the depth distribution of H. griseus in the Black Sea to a significantly shallower zone than other seas of the world. For the moment, no adequate data is available to validate the hypotheses that the bluntnose sixgill shark inhabits a narrow depth range from the surface to 200 metres in the Black Sea. However, this single capture extends the Mediterranean distribution of H. griseus to the Black Sea and confirms its pontic occurrence.
ŠESTEROŠKRGAR HEXANCHUS GRISEUS (BONNATERRE, 1 788) (CHONDRICHTHYES: HEXANCHIDAE), UJET V JUGOZAHODNIH VODAH ČRNEGA MORJA
Hakan KABASAKAL
Ichthyological Research Society, Ataturk mahallesi, Mentejoglu caddesi, idil apt., No: 30/4, Umraniye, TR-34764 istanbul, Turkey
E-mail: hakankabasakal@hotmai l .com
POVZETEK
Dne 19. novembra 2004 se je skoraj 3 milje od obale Amasre (JZ Črno morje, zahodna obala Anatolije) v stoječo mrežo nekega poklicnega ribiča ujel samec šesteroškrgarja Hexanchus griseus (celotna iztegnjena dolžina 300 cm, teža 250 kg). Ta edini primerek potrjuje pojavljanje te vrste v Črnem morju in hkrati podaljšuje njegovo sredozemsko razširjenost do črnomorskih voda.
Ključne besede: Hexanchus griseus, šesteroškrgar, Hexanchidae, Črno morje, razširjenost
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