Tiny Pests Foul Seacage Netting On Fish Farms In Norway

“Wait a moment, and you’ll see how quickly nature can change,” says biologist Jana Günther.

We are clambering together around a fish-farm sea-cage full of salmon. In her orange insulated boiler suit the young German-born SINTEF scientist gets down on her knees and hauls on a rope.

From the sea emerges a piece of greyish net – a sample of coarse netting of a sort often used in the “fences” that hold in the farmed salmon. From its  meshes appears a forest of thin white threads that appear to end in pink pinheads.

“These are living creatures,” explains Günther. Ten years ago, they were not particularly interested in settling down at fish farms in Norwegian waters. Well, I can tell you that times have changed!

My orange-clad companion explains that cultures of these little creatures are now growing rapidly on seacage netting along much of the coast of Norway, and that this type of fouling has left the aquaculture industry with an expensive cleaning task.

“These tiny creatures have shown that if the nets are not cleaned often enough, they can cause serious problems in the course of a short time. In just a few weeks they can form carpets that almost choke the meshes and thus lower the water quality for the farmed fish,” says Günther.

This is the story of these tiny animals that have changed from being good neighbours of the aquaculture industry to troublesome “squatters”. And of Jana, who came from the other side of the Earth with a doctorate on fouling problems, in order to throw them out.

Turned “nasty” during the nineties

In the scientific nomenclature, these creatures 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.

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.

“A serious problem”

Although there is no sign of a “mackerel sky” in the greyish-blue clouds above the fish farm, everything else that is visible around us has to do with fish.

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, the owner, which is one of Norway’s largest aquaculture companies, has given Günther the opportunity to carry out the practical parts of her research here.

Stig Nidar Selvaag’s office is in Hestvika on Hitra, just a few kilometres away. Selvaag is Lerøy Midnor’s aquaculture production manager, and he very much hopes that Jana Günther will be successful.

“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.

Shuttle traffic

Out at the fish farm, Jana Günther has put the fouled piece of netting in a glass container to take it back to her laboratory in Trondheim.

Throughout the autumn, the German biologist has visited the fish farm every three weeks in order to collect samples like this, and to make various measurements.

Back in Trondheim, we meet SINTEF’s Leif Magne Sunde, a scientific veteran in the field of aquaculture technology. He is happy to have Jana, the fouling expert, in his team.

“And if it turns out that we are unable to prevent these hydroids from growing on the nets, we will just have to develop new, simpler cleaning methods,” says Sunde, pointing out that the hunt for a better understanding of the tiny creatures’ preferences is the most sensible way to approach the problem.

“Without more knowledge, all our attempts to deal with this problem will be no better than a shotgun approach; just hoping for the best”