How Many Samples Do You Need to Detect Migratory Fish Spawning with eDNA?

Background A colleague asked a seemingly simple question: “How many water samples would we need to reliably detect a difference in eDNA concentration between a daytime baseline and a nighttime spawning event for a migratory fish species that spawns at night?" A seemingly simple question… So, if you’re trying to detect a spawning event using environmental DNA (eDNA), you’d compare daytime baseline concentrations to nighttime concentrations taken during the spawning window.