Tiny Pest Causes Big Problems for Norway

Tiny animals that have changed from being good neighbours of the aquaculture industry to troublesome “squatters”. Now, Jana Günther, a doctorate on fouling problems, has come to throw them out.

According to a SINTEF report, these creatures are of the family Hydroidae belong to the genus Ectopleura, and their species name is larynx. The textbooks tells us that Ectopleura larynx normally grow on stones in the sea in tidal currents, and that they can also grow on quays and on the hulls of boats, says the report.

According to Jana Günther, cultures of these small animals grew slowly and to only a limited extent on fish-farm nets in Norway until the mid-nineties. Before then, individuals that settled down on such sites often grew side by side with mussels, she says.

“Today, the hydroids grow rapidly on nets, and often as the sole species”.

The fouling specialist has eight years behind her as a student and research scientist in Australia. As a recently joined post-doc. at SINTEF Fisheries and Aquaculture, she is trying to solve the Norwegian fouling problem in collaboration with partners from industry and research. Her goal is to identify practical remedies that will reduce the scale of the problem.

“Could climate change and rising temperatures in the sea be the cause of the rise in fouling?”

“That’s certainly a relevant question,” answers Günther. “It is quite true that higher sea temperatures will increase the number of hydroids and raise the overall level of fouling.”

“But if the climate is to blame, will it not be impossible to solve the fish-farming industry’s fouling problem?”

“We still don’t know whether sea temperature is the main reason that Ectopleura larynx is now able to grow so well on sea-cage netting. I believe that we can at least reduce the severity of the problem as it is today. We will try to improve the situation by looking at several different aspects of aquaculture technology and operation.”

Günther intends to study various possible explanations, such as whether the fouling can have anything to do with the composition of the fish feed, whether it is affected by the type of coating that is used on the nets, and whether net colour affects the readiness of the hydroids to grow on them.

We are on the coast of mid-Norway, in a branch of the sound that separates the island of Hitra from the mainland; this is the island where Norway’s modern fish-farming industry was born.

The XX sea-cages in the sea-farm in front of us house XX salmon. Lerøy Midnor AS, owner of one of Norway’s largest aquaculture companies, has given Günther the opportunity to carry out the practical parts of her research.

“These hydroids are a serious problem for this industry, and it is costing us a lot of money to get rid of them,” he says.

Selvaag explains that Lerøy Midnor uses remotely operated underwater vehicles (ROVs) to clean the bottoms of the sea-cages, and a piece of special equipment with nine rotating discs to clean the sides of the enclosures.

“The cost of purchasing and operating such equipment is high. If the machinery is out of operation for some reason or other, a different sort of cost is involved, because the fish grow more slowly due to the poorer water quality,” says Selvaag.