There is an increase in sightings of a jellyfish that can be deadly for farmed fish, according to The Norwegian Institute of Marine Research.

"There has been as steady stream of new registrations, especially in western Norway," Institute of Marine Research Marine Researcher Tone Falkenhaug said.

Recently, Falkenhaug received around 250 observations of the jellyfish during one week.

This specific jellyfish led to mass mortality in aquaculture facilities in 1997 and 2001, reports the Institute of Marine Research.

In 1997, as many as 12,000 metric tons of salmon died at facilities in Oygarden and Fedje in western Norway, and in 2001, 600 metric tons of salmon were killed by the jellyfish, with the majority of deaths taking place in Trondelag in central Norway.