Growth pattern and population status of the sea urchin Paracentrotus lividus (Lamarck, 1816) on the Mediterranean coast of Egypt

The present study was carried out to evaluate the growth pattern and population status of the sea urchin Paracentrotus lividus (Lamarck, 1816) in the Egyptian Mediterranean coast off Alexandria City. A total number of 2575 specimens were collected from their fishing grounds during 2017 to 2018. The size classes ranged from 9–57 mm with a mean value of 34.27 mm. Classes from 27 to 41 mm represented about 81.44% of the total collected catch. The length-weight relationship (W_t = 0.0039 L^2.3839) reflected a pattern of negative allometric growth. Age was determined using the Bhattacharya’s method based on the length frequency data. Six age or cohort groups were recognized. The Von Bertalanffy growth equations for length and weight were found to be L_t = 71.17[1 – e^{-0.215(t +0.130)}] and W_t = 102[1 – e^{-0.215(t +0.130)}]^2.3839. The estimated longevity t_max for the Egyptian urchin was 13.96 years. The growth indices for length and weight were Φ’_L = 3.04 and Φ’_Wt = 0.67. The values of total mortality (Z), natural mortality (M), and fishing mortality (F) were 1.767, 0.47, and 1.297, respectively. The Egyptian urchin population showed an exploitation ratio of 0.73, indicating an over-exploitation status. The results of the yield per recruit and the relative yield per recruit emphasized the urgent need of fishery management strategies to control the fishing practices of the edible purple sea urchin P. lividus for future sustainability of its wild population off the coast of Alexandria. Further work is also needed to investigate other P. lividus populations along the Egyptian Mediterranean coast and assess their health status.