The deep sea, covering over 60% of our planet, remains Earth's final and most enigmatic frontier. It is a realm of perpetual darkness, immense pressure, and cold, stable temperatures, fostering one of the most unique biospheres. This abyss is home to a staggering diversity of fish communities, from the gelatinous snailfish (Paraliparis) and ancient frilled sharks (Chlamydoselachus) to the vast, bioluminescent shoals of lanternfish (Myctophidae) that form the planet's largest vertebrate migration. For decades, our understanding of these critical ecosystems has been limited by the extreme challenges of access. Traditional methods like deep-sea trawling and submersible operations, while invaluable, are logistically complex, expensive, and invasive, providing only fragmented snapshots of life in the abyss.

Environmental DNA (eDNA) metabarcoding offers a powerful, non-invasive solution to this challenge, allowing us to survey these hidden communities from mere water samples. However, applying this technique in the deep sea is not a simple extension of coastal methods. The unique physics and biology of the deep ocean—from the vertical transport of "eDNA rain" via marine snow to low DNA concentrations and exceptional signal preservation—present a distinct set of methodological hurdles. This workshop aims to bring together researchers to discuss and standardize the novel techniques for deep-water sampling, confront the statistical and ecological challenges of data interpretation, and synthesize our emerging knowledge. Our goal is to build a collaborative framework to robustly apply this revolutionary tool for the exploration and future stewardship of our planet's largest biome.