Stock assessment of holothuroid populations in the Red Sea waters of Saudi Arabia

The present work estimates the stocks of sea cucumbers at sites in the Red Sea — for which there is currently a lack of reliable data. The survey was carried out at 18 sites located in three areas (Al-Wajh, Thowal and Farasan Islands) along the Red Sea coast of Saudi Arabia. The major findings revealed that all sites surveyed were subjected to heavy overfishing that led to high depletion of sea cucumber stocks. Twelve species were recorded during this survey, with the highest diversity recorded at Farasan Islands (eight species), followed by the Thowal area (four species) and the Al-Wajh area (three species). The species included three high value species (Holothuria fuscogilva, H. nobilis and H. scabra), five medium value species (Actinopyga echinites, A. mauritiana, Holothuria atra, H. fuscopunctata and Stichopus variegatus), three low value species (Bohadschia vitiensis, Pearsonothuria graeffei and Holothuria edulis) and one non-commercial species (Holothuria leucospilota). Population structure investigation showed high depletion in populations of H. nobilis, while populations of both H. fuscogilva and H. scabra were completely destroyed. Only H. atra showed a healthy population. 1 National Institute of Oceanography and Fisheries, Red Sea and Gulfs of Suez and Aqaba branch, P.O. Box 182, Suez, Egypt five sites were explored: North Al-Ewandia (underwater reef), Kotaa Al-Ewandia (shallow reef), Shaab Al-Jaziera (shallow reef), Braim Island and Kaad AlJazeira. In Thowal, three sites were surveyed: Bousti (underwater island), Tallah reef and Abou Koussa reef. The Farasan Islands are a group of islands 50 km offshore opposite the Jazan area at the southern borders of Saudi Arabia. Ten sites were surveyed there: Umm El-Hagar (submerged reef), Umm El-Raak (submerged reef), Bagel (submerged reef), Al-Hayla, Al-Shabeen, Umm Al-Madah, Gadeefa (underwater island), Al-Hacece, Al-Sharaa and Abou Atteque. Sea cucumber population assessment methods Estimation of sea cucumber populations at the surveyed sites was carried out using underwater visual transects. Direct visual assessment is the method conventionally used and is effective for the direct enumeration of specimens of epifauna (Lokani et al. 1996). At each site, transects were made covering the different depths, zones and habitats. The length of each transect was about 150 m. Between five and nine replicates were made at each zone and/ or depth. Along each transect 10 quadrats of 10 m x 10 m (100 m2) were made. The shallow areas were surveyed by snorkelling and the deep areas were surveyed by scuba diving. Population estimates and distribution The population density of different sea cucumber species inside each quadrat was counted and expressed as number of individuals per 100 m2. At each quadrat the different biotopes of the reef and type of substrate were described in terms of percentage of sand, rubble, pavement, seagrass, algae, rocks, and dead and live corals. The total population was estimated for each species for all the surveyed sites. The following formula was used to estimate the species population: