Biology of the thornback ray (Raja clavata Linnaeus, 1758) in the North Aegean Sea

The study deals with aspects of the population dynamics in the thornback ray (Raja clavata L., 1758), one of the most abundant cartilaginous fish caught in the North Aegean Sea. Females accounted for 73.08% and males 26.92% of all individuals. Total length of females and males ranged between 50.2 and 89.9 cm (disc width: 33.4–62.0 cm), and between 43.1 cm and 82.7 cm (disc width: 30.7–64.2 cm), respectively. Relationships between total length (TL) and total weight (TW), and between disc width (DW) and total weight (TW) were described by the equations: TW = 0.0041 TL^3.10 and TW = 0.0178 DW^3.03, respectively. Age data derived from vertebrae readings were used to estimate growth parameters using the von Bertalanffy function: L_∞ = 101.71 cm, K = 0.18 y⁻¹, t₀  = −0.07 y for males and L_∞ = 106.54 cm, K = 0.16 y⁻¹, t₀ = −0.28 y for females. The maximum age was 8 years for males and females. Total length at first maturity of males and females was 70.9 cm and 81.2 cm, respectively. Based on the gonadosomatic index and gonadal macroscopic observations, it was determined that the spawning period lasted throughout the year. Stomach content analysis showed that crustaceans (53.03% IRI) and teleosts (14.70% IRI) were the most preferred prey.

Acknowledgements

We are grateful to Dr. Mukadder Arslan İhsanoğlu and Dr. İsmail Burak Daban at the Marine Science and Technology Faculty, Çanakkale Onsekiz Mart University, for their collaboration in sampling and measurements.

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