Sea hares were observed stranded on beaches around the mouth of the Hardy Inlet last month, likely due to oceanographic conditions.
Approximately 1135 animals were observed at the entrance to the Deadwater, the Colourpatch jetty, Jays Beach, and the Ellis Street boat ramp by scientists from the Department of Water and Environmental Regulation (DWER).
DWER scientists observed the stranded sea hares while undertaking their regular fortnightly monitoring as part of Healthy Estuaries WA. High resolution photographs enabled an accurate count of the sea hares in each location.
Most animals appeared to be in healthy condition prior to being washed ashore. Oxygen levels, salinity, and pH were found to be within the normal range for March, with slightly cooler than average sea temperatures.
Scientists believe strong currents and waves caused by strong south and southeasterly winds dislodged the sea hares from their usual habitat amongst rocks or seagrasses in intertidal zones and washed them into the estuary. A strong incoming tidal current also likely played a role, caused by an unusually high spring tide.
Sea hares are large marine gastropods (from the same family as sea slugs and abalone). While safe for humans to handle, some sea hares produce a toxin that can be deadly to animals that lick or ingest them.
The Shire of Augusta – Margaret River was notified of the event and quickly installed signs and issued alerts to warn dog owners of the toxicity risk.
An article about the event has been submitted for publication in the scientific journal Molluscan Research, in collaboration with Dr Fred Wells (Curtin University), Dr Joanna Browne (DWER), Marion Massam (DPIRD) and Hayley Bain (Shire of Augusta – Margaret River).
The conditions also likely caused a large slick of the microalgae Trichodesmium that was pushed into the estuary on the same day and observed by DWER staff. Similar conditions are also believed to have caused a larger stranding of sea hares in 2021, also reported by DWER staff and published in Molluscan Research.
Members of the public who spot stranded sea hares are encouraged to report them to Fish Watch’s 24-hour hotline at 1800 815 507.
