Establishing risk in Norwegian aquaculture
A risk assessment of the national fish farming sector has been commissioned by the Norwegian Directorate of Fisheries to back its management of this industry. But much more needs to be learnt.
Good administration of Norway’s aquaculture sector must be based on facts. So the directorate has sought a risk assessment from the Norwegian Institute of Marine Research.
That will help in evaluating the overall environmental challenges faced by fish farming – a job the directorate does jointly with the Norwegian Food Safety Authority and the Norwegian Environment Agency.
The goal is to assess all possible environmental effects as well as all risk related to the various links in the production chain.
“We compiled our first risk assessment of Norwegian fish farming in 2011,” says Terje Svåsand, programme manager for aquaculture at the marine research institute. “Our latest report, based on data acquired in 2015, was produced in 2016.”
“We took the initiative to draw up the risk report, and our data are an important basis for the assessment,” adds Henrik Hareide, section head in the fisheries directorate’s aquaculture and coastal management department. “The next step is to convert this knowledge into practical administration.”
A primary purpose of the report is to identify the most serious environmental challenges facing the industry so that effective measures can be adopted in the areas of greatest need.
Two issues stand out: salmon or sea lice and escaped farmed salmon. These represent the biggest challenges because they affect large areas with potentially serious ecological consequences.
Sea trout suffer most from lice infection. Unlike salmon, which swim in the open ocean, these fish remain in the Norwegian fjords during the summer and autumn.
They are therefore continuously exposed to the risk of infection by the lice. Arctic char are also vulnerable to a similar threat in northern Norway.
Although infection pressure was relatively low on outwardly migrating salmon in several of the areas investigated, it showed a general rise for outbound smolts from 2014 to 2015.
The threat was highest in Hordaland county, outer regions of Sogn og Fjordane county, the Stordals Fjord in Sunnmøre, Nord-Trøndelag county and Steigen in Nordland county.
“Salmon lice increase in numbers from 1 May, and usually decline during the autumn,” explains Svåsand. “But the level of lice in mid-Norway continued to rise right through to Christmas in 2015. This could be because they’re developing resistance to medicinal treatment.”
One danger posed by escaped salmon is that they can have a genetic impact on unique populations of the wild fish.
The threat that immature adult fish survive until they become sexually active and swim up a river is regarded as smaller than escaped smolts completing their life cycle and crossbreeding with wild salmon.
According to the monitoring programme for escaped farmed fish, the number of such individuals in Norway’s rivers was smaller in 2015 than the year before.
Survey data show that escaped fish accounted for more than 10 per cent of the salmon in 17 of 165 rivers in 2015, compared with 30 of 140 rivers in 2014.
The risk of this proportion being reached is greater when spring smolts escape than when autumn smolts ready to migrate to the sea get out of their cage.
As a result, the Directorate of Fisheries has asked the Institute of Marine Research to develop a table showing minimum mesh sizes for smolt nets to prevent the fish escaping.
“This is an example of the way we first identify important sources of a problem, such as smolt escapes, and can then take effective countermeasures,” says Hareide.
Discharges less serious
The risk that discharges of nutrient salts and organic materials from fish farms will have wider regional effects is still considered to be low.
These substances have an impact beneath the cages and in their immediate vicinity, but virtually all Norwegian fish farms meet a very good or good environmental standard.
A number of these facilities are located close to vulnerable seabed habitats, such as eelgrass meadows and coral reefs.
“Fish farms could potentially affect such vulnerable habitats,” Svåsand observes. “We don’t have an overview of such impacts. We’ll be devoting further attention to this issue.”
Another challenge is the increasing use of medicinal treatments against salmon lice because these parasites are developing resistance to the substances used.
Since this louse is a crustacean, chitin synthesis inhibitors are among the medicinal treatments used. These act by blocking renewal of the louse’s exoskeleton during moulting.
But the chitin inhibitors have the same effect on other crustaceans in the vicinity of the fish farms, such as prawns, crabs and lobsters.
More research is still need to provide sufficient knowledge for evaluating the effects of delousing medications on other nearby organisms exposed to them.
Need to learn more
Despite years of research on the environmental consequences of aquaculture, knowledge gaps remain to be filled.
“We lack sufficient information about the interaction between farmed salmon and wild fish such as saithe,” explains Hareide by way of example.
“We also need better monitoring programmes for escaped farmed salmon in the rivers, broader knowledge about the genetic interaction between these fish and wild stocks, and greater information about the ecological consequences.”
He also wants to see more learnt about the environmental loads affecting new aquaculture locations outside the classic fjord sites with soft seabeds.
A good overview of pathogens in fish farming has been acquired, but few data are available on infections passed from aquaculture to wild fish.
“We’ve assessed the transmission of viruses which cause conditions such as pancreas disease (PD), heart and skeletal muscle inflammation (HSMI) and infectious salmon anaemia (ISA),” says Svåsand.
“Our study indicates that farmed fish pass few such infections to their wild cousins in the sea. But the risk could be greater in the rivers, where fish density is higher. We’re looking at this more closely right now.”
The use of wrasses as cleaner fish represents another knowledge gap. Although this approach might be better at controlling salmon lice than medicinal treatments, too little is known about the possible consequences.
One question is whether moving these fish from one place along the Norwegian coast to an aquaculture facility in another location could have a genetic impact on the local wrasse population.
Others are whether this poses a new infection risk, and whether fishing for wrasses has a negative effect on the local populations where these catches are made.
“Although we’ve updated our knowledge on the use of wrasses, we could still do with acquiring more information,” Svåsand acknowledges.
Fish farmers submit monthly reports on how many fish have died in their cages to the Directorate of Fisheries. These data show that median mortality after 15 months in the sea is below nine per cent. The distribution of farms with high and low mortality is also highly skewed.
Increased mortality could reflect poor-quality smolts, disease or a poor water environment. Handling the fish during delousing increases the risk of higher mortality and a poorer quality of life for the salmon.
The risk assessment of Norwegian aquaculture is to be updated on an annual basis and will be posted on the Institute of Marine Research’s website.