Performance of a trial sea ranch for the commercial sea cucumber, Holothuria scabra, in Papua New Guinea

Holothuria scabra (sandfish) is a tropical sea cucumber that has been over-exploited because of its high-value in the bêche-de-mer trade. It is amenable to mariculture and the potential for community-based sea ranching has been investigated in the Tigak Islands of Papua New Guinea (PNG). A 5-ha trial sea ranch was established within the fishing grounds of an island community and protected from fishing for the duration of this study. Over 10 months, 5655 fluorochrome-marked H. scabra juveniles were stocked into the centre of the sea ranch. Line-transects were used to survey sea cucumber within and on the periphery of the sea ranch prior to stocking the sea ranch (October 2018) and at the conclusion of the study (February 2020). Additional collections of H. scabra were made at night in a 1-ha area around the stocking site. All H. scabra were weighed and checked for fluorochrome marks to determine cultured or wild origin. An estimated 3.7 ± 0.9% of cultured H. scabra were recoverable in the post-stocking survey. Cultured juveniles were found at a significantly higher density only around the stocking site. Factors potentially contributing to low recovery of cultured H. scabra include mortality, being overlooked, migration and misidentification of cultured and wild individuals. Species richness and density of the wild sea cucumber community increased in response to stocking and protecting the sea ranch. Our results highlight the importance of site-specific monitoring and evaluation to assess the success of sea ranching. Despite low recovery, H. scabra mariculture remains a promising option in PNG, as wild stocks are predicted to decline with increased fishing pressure, thus limiting recruitment. This will be aided by improved production of release-size juvenile H. scabra, improved release protocols to promote higher recovery of cultured juveniles and improved community capacity to manage cultured and wild sea cucumber stocks.