Why Lampreys Have Disappeared from South Australian Waters

SARDI researcher Chris Bice said lampreys have not been seen during the last two monitoring periods, raising concerns about the species’ sudden disappearance.

SARDI’s usual catches range from 20 to 100 individuals per cycle, yet the team caught none in the most recent two periods, according to senior researcher Chris Bice.

The absence coincides with a harmful algal bloom that started in March 2025, covering more than 20,000 km² and killing roughly one million marine animals from over 600 species, as reported by the Australian Marine Conservation Society.

Scientists say the bloom was fueled by a combination of floodwater runoff, a coastal upwelling and a marine heatwave, all of which created conditions favorable for the algae.

Lampreys are an ancient, jaw‑less vertebrate that looks like an eel, measuring between 10 cm and 120 cm. They migrate from the ocean into freshwater to spawn and stop feeding once they enter rivers.

To track this migration, SARDI works with SA Water, using fishway traps and large cages to capture and count lampreys each winter.

Chris Bice noted that the unprecedented bloom could be a factor in the missing fish, although he acknowledged that other, still‑unknown reasons might also play a role.

The researchers hope the species will reappear as the bloom’s impact lessens, but they stress that continued monitoring is essential to understand and protect the lamprey population.

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