The comparison of population density of Holothuria tubulosa (Gmelin, 1790) and Holothuria polii (Delle Chiaje, 1823) between exploited and non-exploited areas in the Aegean Sea coast of Türkiye

Abstract

Increasing demand from the Asian market first led to the collapse of economically valuable sea cucumber stocks in the Indo-Pacific, and then demand shifted to lower value Mediterranean species. The effect of this change in sea cucumber stocks in Türkiye started to be seen after the 2010s. To address it, we carried out a study to compare the population density of the most caught Holothuria tubulosa and Holothuria polii species between exploited and non-exploited areas in the Aegean Sea coast of Türkiye. The study was carried out between September 2018 and March 2020 at 4 stations, two of which are in Çandarlı Bay, where sea cucumber fishing is free, and two in İzmir Bay, where it is prohibited. Samplings between 0-20 m depths were carried out with underwater transect line technique, and at depths deeper than 20 m, with beam trawling operations. A total of 6 sea cucumber species were identified, including Holothuria mammata, Holothuria sanctori, Parastichopus regalis and Holothuria forskali species, apart from the target species H. tubulosa and H. polii. Only one P. regalis individual was recorded in the samplings in waters deeper than 20 m. The mean densities of H. tubulosa and H. polii were found to be higher in İzmir Bay stations than in Çandarlı Bay (p<0.05). The results of this study clearly reveal that the population density of sea cucumber in sampling areas has decreased tens of times compared to the last 5 years.