Short Scientific Article	UDC 597.317.7:591.9(262)
Received: 2010-09-09
ADDITIONAL RECORDS OF THE BULL RAY PTEROMYLAEUS BOVINUS (CHONDRICHTHYES: MYLIOBATIDAE), IN THE LAGOON OF BIZERTE (NORTHERN TUNISIA, CENTRAL MEDITERRANEAN)
Olfa EL KAMEL, Néjia MNASRI & Moncef BOUMAÏZA Laboratoire d'Hydrobiologie Littorale et Limnique, Université du 07 novembre à Carthage, Faculté des Sciences, Zarzouna,
7021 Bizerte, Tunisia E-mail: elkamelolfa@yahoo.fr
Mohamed Mourad BEN AMOR Institut National des Sciences et Technologies de la Mer, port de pêche, 2025 La Goulette, Tunisia
Christian REYNAUD & Christian CAPAPÉ
Laboratoire interdisciplinaire de Recherche sur la Didactique, l'Education et la Formation, E. A. 3749, case 77, Université Montpellier II, Sciences et Techniques du Languedoc, 34095 Montpellier cedex 5, France
ABSTRACT
The authors report on the capture of two large bull rays Pteromylaeus bovinus (Geoffroy Saint-Hilaire, 1817) in the Lagoon of Bizerte, a brackish area located in northeastern Tunisia. The specimens were 1110 mm and 1050 mm in disk width (DW), respectively, and weighed 16,200 g and 14,800 g, respectively. They are the largest bull rays recorded in Tunisian waters, a perimediterranean lagoon, and probably in central and southern Mediterranean. Theses captures are commented and discussed.
Key words: Chondrichthyes, Myliobatidae, Pteromylaeus bovinus, Lagoon of Bizerte, northern Tunisia, maximum
size
SEGNALAZIONI AGGIUNTIVE DI VACCARELLA, PTEROMYLAEUS BOVINUS (CHONDRICHTHYES: MYLIOBATIDAE), NELLA LAGUNA DI BIZERTE (TUNISIA SETTENTRIONALE, MEDITERRANEO CENTRALE)
SINTESI
Gli autori segnalano la cattura di due individui di grossa taglia di vaccarella, Pteromylaeus bovinus (Geoffroy Saint-Hilaire, 1817), nella Laguna di Bizerte, area salmastra della Tunisia settentrionale. Gli individui presentavano una larghezza del disco (DW) pari a 1110 mm e 1050 mm, e pesavano 16.200 g e 14.800 g, rispettivamente. Si tratta dei due esemplari di vaccarella piu grandi mai catturati in acque della Tunisia, in una laguna perimediterranea, e probabilmente nel Mediterraneo centrale e meridionale. Nell'articolo tali catture vengono commentate e discusse.
Parole chiave: Chondrichthyes, Myliobatidae, Pteromylaeus bovinus, Laguna di Bizerte, Tunisia settentrionale, taglia
massima
INTRODUCTION
The bull ray, Pteromylaeus bovinus (Geoffroy Saint-Hilaire, 1817), is a typical atlanto-mediterranean species, known in the eastern Atlantic from Portugal to South Africa (McEachran & Capape, 1984) and also off southern Mozambique (Compagno et al., 1989), while in the Mediterranean, P. bovinus is more frequently captured in the eastern than in the western basin, more often in southern areas (Capape, 1989; Zogaris & Dus-sling, 2010). However, the bull ray was previously reported as a rare elasmobranch species in the Adriatic Sea (Soljan, 1975; Jardas, 1985), but recent investigations allow the capture of several specimens and provide thorough data on the life history of P. bovinus from the area (Dulcic et al., 2008).
Southward, P. bovinus was reported throughout the Maghreb shore and especially in Tunisian marine waters (Capape & Quignard, 1975; BradaT et al. 2004). Investigations conducted in Tunisian waters showed that P. bovinus migrated toward northern areas and entered brackish water areas such as the Lagoon of Bizerte (Neifar et al., 1999; El Kamel et al., 2009) and Tunis Southern Lagoon (Mejri et al., 2004). The recent cap-
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Fig. 1: Map of the Lagoon of Bizerte showing the navigation channel (NC), the capture sites of both adult male Pteromylaeus bovinus (black star) and both neonate specimens (black circle; see El Kamel et al., 2009). Sl. 1: Zamljevid Lagune Bizerte z označenim navigacijskim kanalom (NC) ter točkama ulova obeh odraslih samcev Pteromylaeus bovinus (črna zvezda) in obeh novorojenih primerkov (črna pika; glej El Kamel et al., 2009).
tures of two specimens in the Lagoon of Bizerte are herein reported and commented.
MATERIAL AND METHODS
Two bull rays were captured by longline on 08 October 2010 at depths between 8 and 12 m, in the northeastern area of the Lagoon of Bizerte, close to the navigation canal (Fig. 1). The Lagoon of Bizerte is a brackish area located in northeastern Tunisia, between 37"8' N and 37"14' N, and between 9"46' E and 9"56' E. Both specimens were landed at the fishing site of Menzel-Abderrahaman by fishermen. Species identification follows Capape & Quignard (1975) and McEachran & Capape (1984), while morphometric measurements to the nearest mm and mass to the nearest gram follows Mejri et al. (2004). Photographs of both specimens were available.
RESULTS AND DISCUSSION
The two P. bovinus captured in the Lagoon of Bizerte were 1110 mm and 1050 mm in disk width (DW), respectively, and weighed 16,200 g and 14,800 g, respectively (Fig. 2). They were adult males having rigid, calcified and large claspers longer than pelvic fins. Morphometric measurements of both specimens are presented in Table 1. The following description is based on both specimens: head large, snout prominent, narrower than the skull, blunted at the tip. Rostral fins at lower level and separate from pectoral fins along the side of the head. Pectoral fins with outer angle acute strongly falciform. Spiracles large, 3 times as long as wide. Tail slender and elongated with dorsal fin beginning in front of tips of pelvic fins. Pre-orbital horns well-developed.
Fig. 2: Both specimens of P. bovinus captured in the Lagoon of Bizerte, scale bar = 500 mm. SI. 2: Primerka P. bovinus, ujeta v Laguni Bizerte, merilo = 500 mm.
Dorsal surface naked with small tubercles down midline of disc. Dorsal plain brown in adults, slightly darker between the eyes, along the center of the body and the length of the tail. Caudal sting beige. Belly off-white to beige.
Morphology, measurements and colour of both specimens are in agreement with Capape & Quignard (1975), McEachran & Capape (1984), Seck et al. (2002), Dulcic et al. (2008) and Lipej et al. (2009). Such captures once again confirm the migration towards northern Tunisian areas of a species previously considered to have sub-tropical affinities (Postel, 1956; BradaT et al., 2004). Similar instances have been reported in Tunisian waters, and concern elasmobranch species such as the spiny butterfly ray, Gymnura altavela (Linnaeus, 1758) and other teleost species such as the filefish Stephano-lepis diaspros (Fraser-Brünner, 1940) found in the Lagoon of Bizerte (Bdioui et al., 2004) and off Tabarka, a city located close to the Algerian border (Ben Amor & Capape, 2008), the blunthead puffer Sphoeroides pachygaster (Müller & Troschel, 1848), recorded in northern areas by Cherif et al. (2010), and a Lessepsian migrant, the Por's goatfish Upeneus pori Ben-Tuvia &
Golani, 1989, also recently recorded in the Lagoon of Bizerte (Azzouz et al., 2010). Such records could be due to the fact that Tunisian marine waters become warmer than waters in other Mediterranean areas (Quignard & Tomasini, 2000). These records agree with Golani's opinion (Golani, 1998), stating that once a lessepsian migrant species or other alien species arrive to the Mediterranean and establish a self-sustaining population, there are no physical barriers preventing its dispersion everywhere.
The capture of two large bull rays inside the Lagoon of Bizerte shows that the navigation channel does not really constitute the main obstacle for the entrance of large species in the area, as it was previously reported by El Kamel et al. (2009) who noted that only small-sized elasmobranch species were recorded in this brackish area. The bull rays previously found in the Lagoon of Bizerte were two small specimens, probably neonates according to El Kamel et al. (2009). All findings suggest that a sustainable P. bovinus population is at present established in the area, probably due to the fact that in the Lagoon of Bizerte the species has found abundance of mussels, oysters and several gastropod
Sex	male		male	
Total mass (j)	16200		14800	
Morphometric measurements	mm	% DW	mm	% DW
Total length	1600.0	144.1	-	-
Disk length	740.0	66.7	710.0	67.6
Disk width (DW)	1110.0	100.0	1050.0	100.0
Disk depth	90.0	8.1	90.0	8.6
Snout length	110.0	9.9	80.0	7.6
Snout tip to pectoral	115.0	10.4	115.0	11.0
Anterior interspiracular width	120.0	10.8	120.0	11.4
Inter-nasal width	60.0	5.4	60.0	5.7
Mouth width	80.0	7.2	70.0	6.7
Width between first gill slit	140.0	12.6	140.0	13.3
Width between fifth gill slit	96.0	8.6	90.0	8.6
Snout tip to vent	620.0	55.9	590.0	56.2
Pectoral fin anterior margin	540.0	48.6	510.0	48.6
Pectoral fin posterior margin	470.0	42.3	500.0	47.6
Pectoral fin inner margin	111.0	10.0	90.0	8.6
Pelvic fin anterior margin	130.0	11.7	140.0	13.3
Pelvic fin posterior margin	70.0	6.3	90.0	8.6
Pelvic fin inner margin	60.0	5.4	40.0	3.8
Clasper length	110.0	9.9	110.0	10.5
Dorsal anterior edge	75.0	6.8	75.0	7.1
Dorsal posterior edge	65.0	5.9	50.0	4.8
Dorsal base	85.0	7.7	85.0	8.1
Tab. 1: Morphometric measurements and percents of disk width (% DW) of both specimens captured in the Lagoon of Bizerte.
Tab. 1: Morfometrični podatki in odstotki širine telesne plošče (% DW) obeh primerkov, ujetih v Laguni Bizerte.
Tab. 2: Size at birth and maximum size (DW, mm) in male P. bovinus captured in the Lagoon of Bizerte and records given by authors from different marine areas.
Tab. 2: Velikost ob rojstvu in maksimalna velikost (DW, mm) samcev P. bovinus, ujetih v Laguni Bizerte, in podatki avtorjev iz drugih morskih območij.
Area	Size at birth (DW, mm)	Maximal size (DW, mm)	Authors
Coast of Tunisia	250-290	1040	Capapé & Quignard, 1975
Mediterranean	450	-	McEachran & Capapé, 1986
Coast of Senegal	250-270	1150	Seek et al., 2002
Tunis Southern Lagoon	310	-	Mejri et al., 2004
Northern Adriatic	370-450	1135	Dulčic et al., 2008
Lagoon of Bizerte	426-450	1100	This study
species which constitute the main food of P. bovinus (see Capape, 1976). To date, P. bovinus should be considered a marginal species rather than a sedentary one in this restricted area following the definition of Aidan Martin (2005). Additionally, the fishing pressure is rather important in the Lagoon of Bizerte; elasmobranch species such as P. bovinus are consumed by local population with low income and are not discarded at sea after capture (El Kamel et a/., 2009). P. bovinus is vulnerable to fishing pressure because it adheres to K-selected life-histories (sensu McAuley et a/., 2007) as other elasmobranch species, and their recruitment remains difficult. Additionally, recent investigations showed that P. bovinus is not very abundant in the neighbouring shallow coastal waters (Mnasri, 2008).
On the other hand, despite these unfavourable environmental and biological parameters, the observed male
specimens were larger than males previously recorded by Capape & Quignard (1975). As data in Table 2 show, their maximum size was similar to that of bull rays from Senegal (Seck et a/., 2002) and northern Adriatic (Dulcic et a/., 2008). Additionally, they were the largest male P. bovinus and concomitantly the largest elasmobranch ever recorded in a restricted area, a perimediterranean lagoon (sensu Quignard & Zaouali, 1980). Such sizes may be occasional, and could also be the result of the ecological environment of the Lagoon of Bizerte in relation to the food and feeding habits of the species.
ACKNOWLEDGEMENTS
The authors wish to thank two anonymous referees for their useful and helpful suggestions that allowed the improvement of the ms.
NOVI PODATKI O KLJUNATEM MORSKEM GOLOBU PTEROMYLAEUS BOVINUS (CHONDRICHTHYES: MYLIOBATIDAE) IZ LAGUNE BIZERTE (SEVERNA TUNIZIJA,
OSREDNJE SREDOZEMLJE)
Olfa EL KAMEL, Néjia MNASRI & Moncef BOUMAÏZA
Laboratoire d'Hydrobiologie Littorale et Limnique, Université du 07 novembre à Carthage, Faculté des Sciences, Zarzouna,
7021 Bizerte, Tunisia E-mail: elkamelolfa@yahoo.fr
Mohamed Mourad BEN AMOR Institut National des Sciences et Technologies de la Mer, port de pêche, 2025 La Goulette, Tunisia
Christian REYNAUD & Christian CAPAPÉ
Laboratoire interdisciplinaire de Recherche sur la Didactique, l'Education et la Formation, E. A. 3749, case 77, Université Montpellier II, Sciences et Techniques du Languedoc, 34095 Montpellier cedex 5, France
POVZETEK
Avtorji prispevka poročajo o ulovu dveh velikih primerkov kljunatih morskih golobov Pteromylaeus bovinus (Geoffroy Saint-Hilaire, 1817) v Laguni Bizerte, brakičnem območju v severnovzhodni Tuniziji. Širina telesne plošče
(DW) primerkov je bila 1110 mm in 1050 mm, tehtala pa sta 16.200 g in 14.800 g. Gre za največja primerka kljunatih morskih golobov zabeležena v tunizijskih vodah, perimediteranski laguni in po vsej verjetnosti južnem Sredozemlju.
Ključne besede: Chondrichthyes, Myliobatidae, Pteromylaeus bovinus, Laguna Bizerte, severna Tunizija, maksimalna
velikost
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