SOME MORPHOLOGICAL AND BIOLOGICAL ASPECTS OF LONGNOSED SKATE, DIPTURUS OXYRINCHUS (ELASMOBRANCHII: RAJIFORMES: RAJIDAE), IN SYRIAN MARINE WATERS (EASTERN MEDITERRANEAN)

Background. Dipturus oxyrinchus (Linnaeus, 1758) is a common skate in Syrian elasmobranch fishery. This species is listed as an Endangered cartilaginous species on the International Union for the Conservation of Nature (IUCN) Red List. Although heavily exploited, until now, no study has been performed on this skate along the Syrian coast in the Levantine basin. This study focuses on the determination of the reproductive period, size at maturity and fecundity of D. oxyrhinchus. Materials and methods. Total length and total weight were determined for 249 specimens of the longnosed skate, captured off Syrian coast. Skates collected were measured and weighed according to standard procedures. Based on the acquired measurements the following relations were determined: disc width–total weight (DW–TW), total weight–total length (TW–TL), total weight–disc width (TW–DW), and total length–disc width (TL–DW). Median size (TL50) at maturity was estimated according to commonly accepted methods. Hepatosomatic index (HSI) and gonadosomatic index (GSI) were calculated for males and females. The proportion of the occurrence of developmental stages were noted seasonally. Ovarian fecundity was calculated based on ripe follicles in both ovaries of mature females. Fecundity, expressed as annual egg production per female. Tests for significance (P < 0.05) were performed by using ANOVA, Student t-test, and the chi-square test. In the relations TW–TL and TW–DW, comparisons of curves were carried out by using ANCOVA Results. The observed sex ratio was 58.2% ÷ 40.2% (female ÷ male). Mean body measurements of females (n = 14) were slightly higher than males (n = 8). The total length of females ranged from 34.1 to 100.0 cm and males from 34.5 to 81.6 cm. The total length–total weight, disc width–total weight, and total length–disc width relations were TW = 0.0009TL3.35 and TW = 0.0033DW3.34and DW = 0.6894TL + 0.281, respectively, for all sexes combined. Median size (TL50) at maturity were estimated as TL50 = 79.5 cm for females (n = 149) and TL50 = 70.9 cm for males (n = 100). This species had a continuous reproductive cycle. Fecundity was estimated between 50 and 100 egg cases per year. Conclusion. Information on the reproduction of D. oxyrinchus may allow the decision makers to set appropriate catch limits based on biological reference points, and serves as a baseline in the event of increasing exploitation rates. Especially, this information showed that a possible nursery area maybe established in the Syrian marine waters.

skate to 14 t in 2015, and the total production of "sharks, rays, and chimaeras" to about 61 t for the Syrian waters in 2015 (i.e., about 3.8% of the total marine fish production).
Four species of the family Rajidae were recorded off the Syrian coasts: Dipturus oxyrinchus; Raja clavata Linnaeus, 1758; Raja miraletus Linnaeus, 1758; and Raja radula Delaroche, 1809 (see Saad et al. 2006).Dipturus oxyrinchus is commonly captured as bycatch of demersal trawling and longlines throughout the year.In the Mediterranean Sea, there were a few studies on age, growth, biology, feeding behaviour of D. oxyrinchus in central Mediterranean; Tunisian coast (Kadri et al. 2014), Sardinian waters (Bellodi et al. 2016, Mulas et al. 2015), and in Saros Bay, northern Aegean Sea (Yıgın and Ismen 2010).
No studies have been carried out on the reproductive biology or morphology of D. oxyrinchus in eastern Mediterranean, whereas the lack of detailed biological information for the majority of skate species greatly impedes the development of species-specific management strategies for this group (Ebert et al. 2008).
The purpose of the presently reported study was to provide missing information, concerning both sexes of this fish, on body measurements, fecundity, growth parameters, size at sexual maturity estimates, reproductive cycle characteristics (based on morphological changes in reproductive organs), and the seasonal changes in the frequency of individual developmental stages.

MATERIALS AND METHODS Study area and sample collection.
A total of 249 longnosed skate, Dipturus oxyrinchus (Fig. 1), were collected from November 2014 through October 2016.All specimens were captured off the Syrian coast, between Raas Albassit and Tartous, 35°55′N and 34°55′N, by trawling and with bottom longlines, on sandy bottoms, at depths ranging from 50 to 300 m (Fig. 2).Immediately after being captured, the fish were identified, sexed, measured, and weighed.Morphometric measurements.Measurements were recorded for both sexes to the nearest millimetre following Capapé et al. (2015) and expressed as a percent of total length TL.Selected biometric relations.Body was weighed (total weight TW) to the nearest gram.Statistical comparison of disc width-total weight and length-weight relations between sexes combined was performed by ANCOVA (version 20, SPSS).The TL-TW and DW-TW relations were determined using the allometric equations: Maturity.The onset of the sexual maturity was determined in males from the condition and the length of claspers measured following Collenot (1969), and some aspects of the testes and other reproductive organs are given following (Anonymous 2010).Size at sexual maturity was determined in females from the condition of ovaries and the morphology of the reproductive tract following (Anonymous 2010).Five developmental stages were distinguished in males: stage 1 (juvenile/immature), stage 2 (developing/immature), stage 3a (spawning capable/mature), stage 3b (actively spawning/ mature), stage 4a (regressing/mature).On the other hand, developing females were divided into six stages: stage 1 (juvenile/immature), stage 2 (developing/immature), stage 3a (spawning capable/mature), stage 3b (actively spawning/mature), stage 4a (regressing/mature), stage 4b (regeneration/mature).Median sizes at maturity.TL 50 and DW 50 were estimated by fitting a logistic model to binomial maturity data (Mollet et al. 2000).Data were binned into 1-cm DW and TL size classes females and males were analysed separately.The following form of the logistic equation was fitted using least-squares non-linear regression (version 20, SPSS) where Y is the maturity status and x is the total length (or disc width) in centimetres.TL 50 and DW 50 were calculated from the fitted equation as -ab -1 (Mollet et al. 2000).Reproductive cycle.Hepatosomatic index (HSI) and gonadosomatic index (GSI) were calculated in both males and females, respectively as: where LW is the liver weight, GW is the gonad weight, and TW is the total weight.Variations in HSI and GSI related to size and to seasons were considered in all stages of specimens in both sexes, with special regard to variations in HSI and GSI related to size.An ANOVA was used to test the null hypothesis of no significant difference between males and females.Additionally, the percentages of stages developing occurrence were noted seasonally.Fecundity.Ovarian fecundity was calculated based on ripe follicles in both ovaries of mature females.Fecundity, expressed as annual egg production per female, was estimated according to whether females carrying egg capsules were caught (Holden 1975, Oddone andCapapé 2011).

(
) where m is month, P m is the proportion of the capsulecarrying females per month, P max is the highest proportion capsule-carrying females observed, N m is the number of days per month, and E is the mean egg laying rate, considering 0.5 eggs per female, based on the observations made by Holden (1975).Due to sampling problems, P m assumed the value of 0 in some months.In this case, partial fecundity was estimated from last equation and then extrapolated to 12 months to estimate total fecundity.
Frequency DW-TL relations, however, were determined using the formula The coefficients determined from the relations are given in Table 2.
The GSI analysis of adult specimens throughout the year showed that females reach the highest value during the winter and spring (Fig. 13B), while in males, the highest GSI values were in autumn (Fig. 13A).The seasonal evolution of mean HIS values of adults females confirmed the pattern of the GSI, with the highest values in winter and spring (Fig. 14B).In males, no specific trend in HSI was observed (Fig. 14A).
The relative frequency of each maturity stage by season, both for females and males, is shown in Fig. 13.During the sampling period, all maturity stages were recorded, with some variations in their occurrence.Immature male and female specimens were observed throughout the year with a higher percentage of juveniles (stage 1) in spring.Mature females (stage 3a) were found during all seasons with a higher percentage in autumn, females bearing egg cases (stage 3b) found during three seasons winter, spring, and autumn (October to May, except November and April) with a higher percentage in December.Adult regressing females (stages 4a) were observed in winter, spring, and autumn (December to June), while adult regeneration females (stage 4b) were observed in summer, winter, and autumn (June to February, except for September and December) (Fig. 15B).
Mature males were present throughout the year with a higher percentage of active specimens (stage 3b) during autumn months (August to December) (Fig. 15A).Fecundity.The ovarian fecundity in mature females varied from 3 to 30 and from 10 to 26 ripe follicles in right and left ovaries, respectively (mean ± SD, 20.29 ± 6.82 for the right ovary and 18.76 ± 4.64 follicles for the left ovary).There was no significant difference in the number of follicles between the right and the left ovary (paired t-test, P > 0•05).The diameter of vitellogenic follicles varied from 5 to 28 mm with a mean ± SD size of 11.55 ± 6.09 mm.
The number of adult females collected per month is presented in Table 3.Additionally, the mean number of  4).The fecundity estimated using the indirect method was 25.45 eggs per females, since no spawning females were sampled in 6 months (Apr-Jun-Jul-Aug-Sep-Nov); total fecundity was extrapolated for 12 months (~51 eggs per females).Holden et al. (1971) had noted that the rate of egg case laying by the thornback ray in aquaria was one egg case per day and this rate was continuous for 26 days.Should D. oxyrinchus produce one egg case per day its annual fecundity could reach 100, but should egg case production occur every two days, fecundity would be 50.

DISSCUSSION
This is the first study to provide information about morphometric relations, reproductive biology, and the fecundity of Dipturus oxyrinchus in eastern Mediterranean.It is estimated that D. oxyrinchus constitutes about 5.11% (by number) and 1.95% (by weight) of total landings of batoid fishery off Syrian coast through the period of study, and second most abundant species of skates through the year (Alkusairy and Saad, unpublished data).
Mean values of female measurements of were slightly higher than males, this result may be due to the size of sample (8 males and 14 females), or to stage developing, between eight males six were immature; two were mature, but a total of 14 females were immature.
In the presently reported study, females significantly outnumbered males, whereas according to Yıgın and Ismen (2010), Kadri et al. (2014), andBellodi et al. (2016) both sexes were equally distributed.This might have been the result of the bathymetric distribution by sex and the fishing  2016) reported that a dominance of D. oxyrinchus females was observed in the deepest waters (501-800 m).
In addition, the range size of males was smaller than that of females.The occurrence of sexual differences in growth is well documented in elasmobranchs, with females usually growing larger (Başusta et al. 2008, Yıgın and Ismen 2010, Alkusairy et al. 2014, Kadri et al. 2014, Bellodi et al. 2016, Girgin and Başusta 2016, Ali unpublished).Previous studies providing length-weight relations for D. oxyrinchus are given in Table 5, for comparative purposes.
In Syrian marine waters, the respective values of TL and DW of D. oxyrinchus at maturity were 70.9 cm, and 48.2 cm for males and 79.5 cm and 54.8 cm for females, corresponding to about 86% of the maximum values observed TL and DW in males and 80% of maximum observed TL and DW in females.Cortés (2000) and Ebert (2005) stated that skates tended to mature between 75% and 90% of their maximum size.Data reported by Ebert (2005), indicate that this species could be particularly sensitive to fishing pressure and overexploitation.
Large size at maturity, with females maturing larger than males, was previously observed in other Mediterranean areas such as the north Aegean Sea (Yıgın and Ismen 2010), southern Tunisia (Kadri et al. 2014), and Sardinian waters (Bellodi et al. 2016).However, these studies reported larger sizes of TL 50 , except for Yıgın and Ismen (2010) who reported smaller size of DW 50 (Table 6).The pattern of difference in size at maturity between regions might be partly explained by differences in sample size, sampling method, and different rates of maturation due to different environmental conditions (Girard and Du Buit 1999), or  in winter and spring, while in males no specific trend in HSI was observed, probably because they appear to be reproductively active throughout the year.This result has been confirmed by the fact that all maturity stages were recorded throughout the study period, Immature males and females were observed in all sampling seasons with a seasonal peak in spring and females were carrying fully developed oocytes and egg cases throughout the year (except summer months).While some of the hepatic reserves can be used in producing gametes in female oviparous elasmobranch species, the role of the liver in reproduction in male elasmobranchs is still not completely understood (Craik 1978, Garcia-Garrido et al. 1990).Continuous reproduction throughout the year for Dipturus oxyrinchus was also reported by Kadri et al. (2014) in Tunisian waters and in Sardinian waters (Cabiddu et al. 2012, Bellodi et al. 2016).On the other hand, Stehmann and Burkel (1984) and Notarbartolo di Sciara and Bianchi (1998) reported that the spawning period for this species lasted from February through April, and from February through May (Serena 2005) (Table 6).Continuous reproduction, either with or without seasonal peaks was also suggested for other congeners such as Dipturus nidarosiensis (Storm, 1881) (see Follesa et al. 2012) and several other skate species for example Bathyraja parmifera (Bean, 1881) (see Matta 2015).Year-round reproduction may be a strategy to compensate for late maturity and high maternal energy investment, or it could be a consequence of bet-hedging (Seger and Brockmann 1987), maximizing long-term fitness and increasing the probability of juvenile survival (Bellodi et al. 2016).Spawning active males occurred mainly during the autumn and winter months, and extruding females were mostly found during winter and autumn.This asynchrony suggests that populations could be sexually segregated and mating could occur during to egg-laying, while Bellodi et al. (2016) reported that reproductively active males, however, occurred mainly during the summer months, while reproductively active females were mostly found during autumn and winter.
Oviparous elasmobranchs are not very prolific, as is already known.When skates were compared with that of    different fishing pressure (Aranha et al. 2009).However, reproductive biology differences with other studies might result of populations or even species differences, indeed it has been suggested that D. oxyrinchus could be a species complex as it was demonstrated was for Dipturus batis (Linnaeus, 1758) (see Dulvy et al. 2006).Seasonally variations were found in the gonadosomatic and hepatosomatic indices of males and females of Dipturus oxyrinchus.The highest values of GSI in females were observed in spring and winter, while in autumn-in males.The highest values of HIS in females were noted other elasmobranch fishes, fecundity in skates would be high, especially in relation to viviparous species (Oddone and Capapé 2011).The fecundity of Dipturus oxyrinchus in Syrian marine waters ranged from 50 to 100 egg cases per year.The fecundity previously assessed for rajoid specimens from British marine waters by Holden et al. (1971) and Holden (1975) was, respectively, 150 and 140 egg cases per year.Capapé (1976) reported a fecundity of 141-167 for R. clavata from the northern Tunisian coast and Capapé et al. (2007b) one of between 108 and 162 for specimens from the Languedocian coast, southern France.Capapé and Quignard (1975) noted that the respective fecundity of Raja miraletus and R. radula from the Tunisian coast ranged from 40 to 72 and 80 to 154 egg cases.On the other hand, Capapé et al. (2007a) estimated the fecundity range of R. miraletus from the Senegalese coast at between 71 and 178 egg cases.Serra-Pereira et al. (2011) noted during spawning season that the total fecundity was around 140 eggs per female of R. clavata from Portuguese waters.Oddone and Capapé (2011) reported that fecundity of Rioraja agassizii (Müller et Henle, 1841) ranged from 62 to 124 egg cases per year from south-eastern Brazil.The fecundity estimation of D. oxyrinchus falls within the range observed for other rajoid species.
The data in this study, concerning some traits of the reproductive biology of Dipturus oxyrinchus off Syrian marine waters, showed that a possible nursery area of this species was probably established.Conversely, D. oxyrinchus is presumed to be in decline and 'near threatened' in the Mediterranean (Ellis et al. 2015).Finally, all these information, which is confirm a crucial factor to successful conservation and management of the longnosed skate in Syrian marine waters.Similar studies on others species are also needed especially in the region and generally in other Mediterranean regions.

Fig. 7 .Fig. 8 .Fig. 9 .Fig. 10 .
Fig. 7. Box-and-whisker plot with the mean, standard deviation, range of total length for males (A) and females (B) of Dipturus oxyrinchus captured in Syrian marine waters, separately at each maturity stage

Fig. 15 .
Fig. 15.Seasonal distribution by stages for males (A) and females (B) of Dipturus oxyrinchus captured in Syrian marine waters

Table 1
Proportional measurements expressed as a percent of total length of males and females of Dipturus oxyrinchus captured off Syrian coast

Table 2
Selected morphometric relations of Dipturus oxyrinchus captured off Syrian coast

Table 3
Seasonal diversity of selected biological parameters of adult females of Dipturus oxyrinchus captured off Syrian coast

Table 5
Principal biometric relations of Dipturus oxyrinchus from different regions W = 0•0009TL