For the first time, scientists have decoded years of underwater “grunts” made by groupers to reveal how and when they spawn. The study, spanning more than a decade of recordings in the Gulf of Mexico and Western Atlantic, shows that fish sounds can provide vital clues for monitoring populations and detecting changes linked to climate and fishing pressure. 

The study

Researchers analysed over 270,000 hours of recordings collected by passive acoustic monitoring devices. Distinctive grouper grunts were identified and linked to spawning activity across five species, including red and gag grouper. The calls often occurred at night and during lunar cycles, reflecting long-recognised patterns in reef fish reproduction.

Key findings

The sound analysis confirmed known spawning sites and revealed shifts in timing and intensity of calls at others. For example, gag grouper vocalisations declined in areas where populations have dropped, while red grouper showed more stable patterns. The results suggest that acoustic monitoring can be a powerful tool to track both abundance and reproductive health.

Why it matters

Groupers are commercially valuable but vulnerable to overfishing, particularly during spawning aggregations when they gather in large numbers. By decoding their vocal behaviour, scientists can detect spawning events without intrusive surveys and monitor changes over time. This approach may also help forecast how climate change affects reproductive timing and site use.

Next steps

The research team hopes to expand the use of passive acoustic monitoring across wider reef systems, building long-term sound archives. These data could inform more adaptive fisheries management and protect critical spawning grounds before they are depleted.