Optimising methods for community-based sea cucumber ranching: Experimental releases of cultured juvenile Holothuria scabra into seagrass meadows in Papua New Guinea

•Short-term caging did not increase survival of cultured juvenile sandfish released into the wild.•Free (no-cage) releases of cultured sandfish resulted in comparatively high survival.•Sandfish survival and growth varied significantly among sites differentiated by habitat and productivity variables.•Principal components analysis clearly separated the best and worst release sites.•Test plots could be useful to assess site suitability prior to large-scale release of sandfish.

Hatchery-cultured juveniles of the commercial holothurian, sandfish (Holothuria scabra), were used for release experiments in a variety of marine habitats under traditional marine tenure near Kavieng, Papua New Guinea (PNG). Juveniles of approximately 4 g mean weight were released inside 100 m2 sea pens installed within seagrass meadows nearby partner communities, under the care of local ‘wardens’. Within each sea pen, varying levels of protection (free release, 1-day cage and 7-day cage) were provided at release in order to determine if short-term predator exclusion improved survival. Ossicles of juvenile sandfish were tagged with different fluorochromes for each treatment and sandfish survival and growth was recorded after release. A range of biophysical parameters were recorded at the four sites. Contrary to expectations, short-term cage protection did not lead to higher survival at three sites, while a fourth site, despite meeting all considered criteria for suitable release habitat, experienced total loss of juveniles. There were significant differences in mean weight of juveniles between sites after four months. Multivariate analysis of biophysical factors clearly separated the sea pen habitats, strongly differentiating the best-performing site from the others. However, further research is needed to elucidate which biophysical or human factors are most useful in predicting the quality of potential sea ranch sites. Methods developed or refined through these trials could be used to establish pilot test plots at potential ranching sites to assess site suitability and provide guidance on the level of animal husbandry required before commencing community sea ranching operations in New Ireland Province, PNG.