New sighting of the endangered species blackchin guitarfish, Rhinobatos cemiculus, in the South Aegean Sea

Abstract

Background

A new record of the endangered species blackchin guitarfish, Rhinobatos cemiculus (925 mm TL) is here reported from South Aegean Sea. On 11 January 2015, a single specimen was collected by longline off from the Kuşadası Bay, Turkey. This new finding confirms the presence of the species along the Anatolian coasts of Aegean Sea and shows that the species is occuring in the South Aegean Sea.

Results

Rhinobatos cemiculus belonging to family Rhinobatidae was identified and its distribution was compared for the Aegean and Mediterranean Sea based on literature. The main identification and some measurements of morphometric characteristics were given.

Conclusions

In terms of distribution of fish taxa, Aegean coasts of Turkey has the highest diversity with 449 species, which of 64 species belong to Elasmobranchii. This report aims to close information gaps in distribution endangered cartilaginous fish throughout the Turkish Aegean coasts.

Background

The family Rhinobatidae consists of 52 species worldwide, two of which have been found to occur in the Mediterranean (Rhinobatos cemiculus Geoffroy Saint-Hilaire 1817 and Rhinobatos rhinobatos (Linnaeus 1758)). Rhinobatos cemiculus is widely distributed eastern Atlantic from Portugal to Angola (McEachran and Capapé, 1984), mostly on sandy and muddy bottoms to maximum depth of 100 m (Capapé and Zaouali, 1994). It is a prevalent Guitarfish in the Central Mediterranean Sea (i.e. Gulf of Gabés) (Echwikhi et al. 2013) and North eastern Atlantic (e.g. Senegalese coast) (Seck et al. 2004).

In the Mediterranean, it has been reported from France (Capapé et al. 2006) Italy (Tortonese, 1956), Morocco (Lloris and Rucabado, 1998), Tunisia (Mejri et al. 2004; Echwikhi et al. 2013), Turkey (Iskenderun Bay: Başusta et al. 2012), and Israel (Ben-Tuvia, 1953; Golani, 1996) whereas its occurrence is rarely documented along the Hellenic and Anatolian coasts of Aegean Sea, and to date only a few records from Rhodes Island (Corsini-Foka, 2009) and Izmir Bay (Akyol and Capapé, 2014) are known (Fig. 1).

Fig. 1

Map showing the locations of Rhinobatos cemiculus records in the Aegean Sea (1-Corsini-Foka (2009), 2- Akyol and Capapé (2014), 3-Present study)

Rhinobatos cemiculus is considered as a target species in small-scale fisheries but on the other hand it is known by-catch in several non-target fisheries, especially in bottom trawl fisheries (Enajjar et al. 2012). Due to its commercial interest, overfishing of mature females (that are aplacental viviparous and not prolific) poses a threat for resilience and conservation of this species (Echwikhi et al. 2013). Therefore, it is listed as “endangered” according to the IUCN Red List of Threathened Species (IUCN, 2014).

This study is to report on a new record of R. cemiculus from Kuşadası Bay confirming the presence of the species in the Aegean Sea.

Results

Brief description of the specimen in formalin

Body very elongate and flattened, covered with small dermal denticles; wedge-shaped snout with rostral ridges narrowly separated. Distance between rostral ridges less than eye diameter. Anterior nasal lobes not reaching to level of inner corner of nostril (Fig. 2). Eyes relatively small. Numerous small teeth in payement pattern on jaws. Of the well-developed two dorsal fins the first beginning behind hind tip of pectoral fins. Thorns situated around inner margins of orbits, between spiracles and on shoulders, along midline of body and tail. Dorsal colouration olive green to brown, pale white below; snout and rostral ridges semi-transparent, beige upper limbs of dorsal fins. Selected morphometric (in mm) values of R. cemiculus were measured as follows: TL 925 mm, precaudal length 787 (85.1 % TL), disc length 280 (30.2 % TL), disc width 315 (34.0 % TL), orbit diameter 12 (1.3 % TL), predorsal length 182 (19.7 % TL), preorbital length 162 (17.5 % TL), interorbital width 52 (5.6 % TL), preoral length 182 (19.7 TL), mouth width 64 (6.9 % TL).

Fig. 2

Rhinobatos cemiculus collected from Kuşadası Bay, January 2015 (a) Total dorsal view, (b) left nostril (scale bar = 200 mm)

Discussion

According to the previous records of R. cemiculus in the Mediterranean, this species is considered as a rare fish and its eastward distribution appears to be limited in the South Aegean Sea (Fig. 1).

To evaluate the settlement success of any species, information on reproduction of the species is required. In the Mediterranean, Capapé and Zaouali (1994) reported that females of R. cemiculus reach maturation at 1000 mm TL (Tunisian waters) while Ali et al. (2008) in Syrian coasts and Enajjar et al. (2012) in Gulf of Gabès observed for females a length at first maturity of 873 mm TL and 1381 mm TL, respectively. The specimen collected in this study was immature, as no developing or ripe oocytes, embryos and fetuses were observed by dissection. The sexual maturity and maximum length range in fishes can be affected by a number of factors, such as temperature, food availability, light regime, oxygen, salinity, pollutants, predator density, genotype and overfishing (Bone and Moore, 2008). On the basis of our findings, it is not possible to report the presence of a breeding population of the species in the South Aegean Sea. Further research and monitoring studies are strongly suggested to clarify the population status of R. cemiculus in this area.

Conclusions

On the basis of citizen science, we observed and reported blackchin guitarfish, Rhinobatos cemiculus, from the South Aegean Sea. This study provides a prior knowledge about distribution range of endangered elasmobranch species in the Aegean Sea for biologists.

Methods

On 11 January 2015, a single female specimen of R. cemiculus (925 mm total length (TL)) (Fig. 2) was collected by longline from Kuşadası Bay (37°52′N, 27°13′E) on a sandy bottom at a depth of approximately 20 m. The specimen was taken to the Laboratory of Fisheries Faculty of Muğla Sıtkı Koçman University (Turkey), for further examination, where the main morphometric measurements were collected by means of a digital calliper (to the nearest 0.01 mm). The individual was identified based on criteria by McEachran and Capapé (1984), based on its morphometric measurements. Following the identification, it was fixed in 4 % formalin and cataloged in the Faculty of Fisheries of Muğla Sıtkı Koçman University Collection Museum under the number MUSUM/PIS/2015-2. Scientists are welcome to have access to the biological material at will.