The swordfish (Xiphias gladius) that washed up near Eemshaven in Groningen earlier this month may have died from asphyxiation after swallowing mud, experts have said.

There has been no autopsy yet, but, Ecomare education manager Pierre Bonnet said, the likely cause is that the animal inhaled mud while in shallow, muddy water. An earlier theory was that the animal died of starvation after getting lost. Swordfish typically live in tropical waters.

“You could see its gills were full of mud,” Bonnet told local broadcaster RTV Noord. “It probably panicked. The sea bottom is extremely muddy, and it would have sunk some 30 centimetres into it,” Bonnet said.

Just three swordfish are known to have washed up on Dutch shores in the past 100 years. The last one was found in 1986.

The swordfish is currently in a freezer at Ecomare awaiting an investigation of its stomach contents at Wageningen University. Before that, the Wadden Sea centre wants to make a replica of the animal to put in its collection.

Bonnet said he didn’t expect there to be an official cause of death. That only happens if mammals wash ashore, not fish, he said.