Handfish (Family Brachionichthyidae) comprise 14 extant species, many of which are endemic to Tasmanian waters. They are considered the world's most threatened family of marine bony fishes, with seven species currently listed as Endangered or Critically Endangered on the IUCN Red List. While substantial monitoring effort has focused on spotted and red handfish populations in shallow coastal habitats, the status of several other potentially threatened species remains poorly understood due to their low encounter rates and deeper distributions.
Recent observations of handfish in imagery collected from Australian Marine Parks off southern Tasmania suggest that previously undocumented populations may occur in mesophotic shelf habitats (>50 m depth). Here, we present results from targeted handfish surveys conducted in Huon and Tasman Fracture Marine Parks using a novel integrated sampling approach. Surveys employed a remotely operated vehicle (ROV) equipped with high-definition video cameras for visual detection, together with a custom-designed Niskin bottle sled for environmental DNA (eDNA) collection. Species identifications were confirmed using a combination of visual assessments and genetic analyses of eDNA samples collected in close proximity to observed individuals.
Our findings provide important new insights into the distribution of handfish species in Tasmania and highlight the conservation significance of mesophotic habitats. The study also demonstrates the value of combining ROV and eDNA technologies for the detection, identification, and long-term monitoring of handfish populations in Australian Marine Parks and other deep-water environments.