Meet Holothuria scabra, sometimes called the sandfish. Despite its name, this tubular creature isn’t a fish at all – it’s a sea cucumber! Sea cucumbers (sometimes called holothurians or holothuroids) are fascinating ocean animals that come in all shapes and sizes. They live on the seafloor (some species can swim!) in both shallow and deep waters. Like sea urchins and sea stars, they’re echinoderms – but with a more cylindrical body. Check out this recent Water Column for more info on sea cucumbers.
Holothuria scabra is one of the sea cucumber species that was assessed at the workshop.
Holothuria scabra is a relatively well-known tropical species often found throughout the Indo-Pacific region, from East Africa to the central Pacific. As its common name suggests, it exhibits a distinctive behavior: burrowing in the sand – sometimes to escape the cold (as adults) and sometimes to avoid light (as juveniles). But there’s another trait that makes this species especially interesting for SOSA’s Red List team: it is commercially fished.
Commercial fishing is one of the biggest threats facing sea cucumbers. That’s why it was a major topic of discussion earlier this month at the Holothuroidea Red List Workshop, where 7 sea cucumber experts from the IUCN SSC Sea Cucumber Specialist Group gathered to assess the global extinction risk of various species. The workshop was organized by SOSA via the Marine Invertebrate Red List Authority (MIRLA), which works to increase the number of marine invertebrate species – like sea cucumbers – assessed for the IUCNRed List.
Many sea cucumbers were last assessed over a decade ago, creating an urgent need to update data, reflect current threats, and include additional species. Once completed, these assessments will contribute to the IUCN Red List of Threatened Species, the world’s most comprehensive source of species conservation data.
Dr. Anne Helene Tandberg, SOSA’s Red List Coordinator, kicking off the Holothuroidea Red List Workshop.
Data for completing an assessment can come from many sources. Fundamental science plays a key role — for example, academic researchers studying the ecology and biology of sea cucumber species often conduct population surveys that inform assessments. Fisheries can also be valuable sources of information, but their data typically group all sea cucumbers together without distinguishing between species. By-catch species — which are still harvested and sold for consumption — are almost never recorded separately.
And that only covers the fishing we know about. Illegal sea cucumber harvesting remains widespread, making it nearly impossible to gauge its full impact on wild populations.
When assessing extinction risk, SOSA’s Red List Coordinator, Dr. Anne Helene Tandberg, explained that fisheries data can provide important insights — but it is often fragmented or incomplete. As she put it:
“Piecing together data from different sources — like fisheries, scientific research, or markets — is like assembling a very complex puzzle, where many of the pieces are missing or the wrong shape.”
For the assessments, experts needed to calculate population changes in the sea cucumber species over three generations, one of the key Red List metrics. This meant not only compiling data from multiple countries (since species’ ranges can span multiple geopolitical borders) but also agreeing on the species’ generation length – this is calculated from information about how long individuals live and when they begin reproducing. Which are two notoriously challenging metrics to acquire for sea cucumbers!
Because H. scabra is also farmed in aquaculture facilities, assessors had access to reproductive data not typically available for wild populations. However, a key question remained: Is reproduction in captivity the same as in the wild? The team also debated the species’ lifespan. For many animals, size correlates with age – but not for sea cucumbers. Their size reflects food availability: they can grow or shrink depending on environmental conditions, so assessing their age and thus lifespan is very tricky.
The case of Holothuria scabra illustrates the complexity of assessing sea cucumber populations – even for species we know relatively well. For many others, information is far scarcer. That’s exactly why assessing these animals – and marine invertebrates in general – is so critical for conservation.
This workshop marks the beginning of a broader sea cucumber assessment effort, focusing first on species that are commercially fished and listed under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
“There are several commercially fished species where data simply isn’t being collected in fisheries inventories. We hope that by providing Red List assessments and data on global threats, we can help create pressure to start properly monitoring these vulnerable species.”
