Tropical sea cucumbers are in peril due to overharvest. Sixteen species are endangered or vulnerable (IUCN) with high-value teatfish recently listed on CITES Appendix II. We reviewed the Queensland Sea Cucumber Fishery, which harvests CITES-listed black teatfish (Holothuria whitmaei) and white teatfish (H. fuscogilva), and other IUCN-species, from the Great Barrier Reef (GBR), Australia. Teatfish harvest on the GBR has experienced serial catch reductions and fishery closure due to local depletion, a trend observed globally for sea cucumbers and of concern for the at-risk GBR World Heritage Area. We provide the first case study for teatfish while their trade continues, and highlight other species of concern. For example, the major target species of the fishery, Actinopyga spinea (~ 50% of total catch), is not a traditional species in the global trade. With over one million individuals harvested annually, its fishery and its ecological consequences require attention. We synthesise knowledge on teatfish population parameters, identify knowledge gaps and suggest measures to reduce fishery impacts. Continued global exploitation of at-risk marine invertebrate species, coupled with scientific uncertainties, emphasise the urgent need for targeted research and to apply the precautionary principle to avoid detrimental outcomes in their conservation status.