Optimizing the use of portable ROVs for community-based benthic surveys: A case study on the demographics of sea cucumbers around nursery habitats in the Arctic

Nearshore areas around Qikiqtait in the Canadian Arctic have been identified as nursery habitats for the sea cucumber Cucumaria frondosa , which is locally consumed and being explored for small-scale commercial fisheries. This study characterized this species’ demographics along a depth gradient (∼0.5–11.5 m) at three sites inside and adjacent to nursery grounds using a mini-class remotely operated vehicle (ROV). A novel technique involving the superimposition of virtual quadrats was developed to minimize perspective biases for the analysis of images captured obliquely relative to the seafloor. Overall densities at Katak and Kataaluk were a magnitude lower than at Sanikiluaq, suggesting spatial variability in environmental conditions. Smaller individuals (∼5 cm) occurred mostly on rubble between 1–3 m at Sanikiluaq, larger ones (∼10 cm) on gravel at 2–7 m at Kataaluk, and a mix of both size classes occupied gravel, rubble, boulders, and bedrock between 3–11 m at Katak. Globally, body sizes tended to increase with depth, evoking cohorts of sea cucumbers undergoing step-wise downward migrations as they grew. This study provides foundational data on C. frondosa around its nursery habitats. It also enhances the usefulness of mini-class ROVs to investigate benthic assemblages in ice-covered areas through community-led initiatives.