The aims of this project were to develop large scale breeding and rearing methods for sandfish (Holothuria scabra) for commercial culture and/or restocking. Wild collected sea cucumbers were initially difficult to spawn, but after a period in earthen ponds or seabed pens could be induced year-round, using temperature changes, emersion, treatment of water with UV light, and addition of dry phytoplankton. Numerous batches of larvae were reared to settlement and to larger sizes using simple hatchery methods.
Overfishing threatens to extinguish local fisheries for valuable tropical sea cucumbers by reducing population densities to the point where reproductive success trails behind natural mortality (known as depensation or the ‘Allee effect’). Once this happens, conventional management measures alone, such as closed seasons/areas, size limits and gear restrictions, will usually fail to repair the damage. A different suite of active management interventions must be considered to restore the spawning biomass of severely over-exploited populations.
Sea cucumbers processed into beche-de-mer are a valuable source of income for many coastal communities in the developing nations of the Indo-Pacific. Increasing demand from China has caused overfishing of stocks of the high-value species. The potential to restore populations of tropical sea cucumbers and then sustain increased yields by stock enhancement is being assessed in a number of countries including Ecuador, India, Kiribati, Maldives, the Marshall Islands and the Solomon Islands.
This article provides an overview of the sea cucumber fisheries in the Philippinee, covering topics of 1) trade, 2)socioeconomic importance to local community 3) recommendations for improving fisheries management and conservation of sea cucumber populations.
In this study, we examined the growth of juvenile Actinopyga mauritiana in captivity at three levels of stocking biomass, and under two feeding regimes, for 12 months. We chose this species because of its availability on intertidal reefs in the Solomon Islands, its relatively high value.
Development of the tropical sea cucumbers Holothuria scabra, H. fuscogilva and Actinopyga mauritiana was investigated. Holothuria scabra developed through the feeding auricularia, the non-feeding doliolaria and the pentactula larval stages in 14–17 days at 26–28°C. Holothuria fuscogilva and A. mauritiana were reared to the auricularia and doliolaria stages respectively. The auricularia stage was reached by 40–70 h and the larvae developed lateral processes and a prominent ciliated band. Transformation to the doliolaria stage took 10–12 h and occurred on Days 9–12 in H.
Two little known species of Holothuria (H. theeli and H. portovallartensis) were observed in the Galapagos Islands.
Access to technology for producing and releasing juveniles is not a sufficient rationale to proceed with restocking (restoring stocks to the point where they can sustain regular harvests) or stock enhancement (increasing yields by overcoming recruitment limitation) of sea cucumber populations. Rather, careful decisions need to be made about whether these interventions are likely to be cost-effective ways of improving productivity.
Large-scale releases of cultured “sandfish,” Holothuria scabra, were used to examine size- and density-dependent effects on survival among sites. Juveniles were marked by fluorochromes in 3 size classes and released into open 500-m2 sea pens. A preliminary trial involved the release of 4,000 juveniles at two sites. In a subsequent large-scale experiment, we released 9,000 juveniles at 0.5, 1, or 3 individuals m-2 at 4 sites. Growth and survival up to 2 years post-release were estimated from successive recapture surveys and marker verification.
Seven tank trials were undertaken involving the co-culture of sandfish and shrimp on sand. Sizes, stocking densities, feeding and other conditions were all varied. Results indicated that powdered sargassum did not support sandfish growth, although it may have prevented starvation, which otherwise killed juveniles within three to six weeks.