fish health

Salmon escapes and mortality rates in Norway

Salmon escapes

According to the Norwegian Prime Minister, Erna Solberg, the Norwegian government aims to grow Norwegian salmon production, but within an environmentally sustainable framework.  Control of the sea lice and salmon escapes are the high-priority items.

salmon escapes“In order to grow, environmental considerations will be important. The industry will have to solve the challenges of lice and escapes.”


The number of escaped salmon and escape incidents varies from year to year. However the trend is that both numbers are declining (the below chart is updated 30.05.2015).

Why is the control of salmon escapes important?

The message from the Norwegian Fishery Directorate is that escaped farmed salmon can interbreed with wild salmon in the rivers and thus may have negative impact on the wild salmon.

Sterile farmed salmon cannot interbreed with wild salmon. Trials with sterile farmed salmon are in progress, but some challenges, especially related to fish health, remain before the authorities may require the compulsory use of sterile farmed salmon in commercial fish farming.

According to the government and the Directorate, to prevent escaped incidents the most important measures are to impose strict requirements to the design of the fish farming facilities and to have good operating routines.

Fish farmers are required to immediately report any suspicion of salmon escapes to the Norwegian Directorate of Fisheries. They are also required to take steps to capture escaped fish. Failing to report suspected salmon escapes is a criminal offence.

The Norwegian Directorate of Fisheries publishes all information on its website.

Salmon mortality

There are currently three generations of salmon in the sea: the 2013G, the 2014G and the 2015G

Accumulated mortality on the 2013G is 13%. This is in line with the mortality rate for the 2012G but better than the historical average of 17%.

The 2014G is also performing well. 9% of the 2014 has died YTD, which is  the same as last year for the 2013G.

3 reasons why I pay attention to fish health and mortality
  1. Salmon mortalities is a fish health indicator. Elevated mortality after a few months in the sea is normally related to outbreaks of disease or predator attacks.
  2. Salmon mortalities could increase with high and low seawater temperatures.  When temperatures are high, the disease risk increases, and with temperatures below 0C, there could be mass mortality.
  3. High mortality means higher production costs. However under normal circumstances, mortality normally makes up around 1% of the total production cost in salmon farming.

In Norway, a total of 290 million smolts were released in 2013 (2013G). By the end of April 2015, the number of 2013G in the sea has been reduced to 33 million, according to SjømatNorge.

Hence, since 1 January 2013, the number of 2013G still alive has been reduced by 257 million units (89%). 39 million fish individuals have been lost to mortality while 218 million units have been harvested or escaped.

How to  think about salmon mortalities

Most of the following can be found in Marine Harvest Handbook 2014. During the salmon’s production cycle, some mortality will be observed. Under normal circumstances, the highest mortality rate will be observed during the first 1-2 months after the smolt is put into seawater, while subsequent stages of the production cycle normally has a lower mortality rate.

Elevated mortality in later months of the cycle is normally related to outbreaks of disease or predator attacks. With high seawater temperatures, disease risk increases, and with temperatures below 0C, there could be mass mortality.

It is not possible to perform biological production without any mortality. However, during the last two decades there has been a general stabilisation of mortality in Norway which has been achieved principally through good husbandry, management practices and vaccination.

Today, mortality normally makes up around 1% of the total production cost in salmon farming.

There is no strict standard for how to account for mortality in the books, and there is no unified industry standard. However, by capitalizing the mortality cost, the cost of harvested fish will therefore reflect the total cost for the biomass that can be harvested from one production cycle.

Diseases that can result in elevated mortality

Infectious Pancreatic Necrosis (IPN): IPN is caused by the IPN virus and is widely reported. It is a contagious virus that can cause mortality if not managed appropriately. IPN can affect Atlantic salmon fry, smolts and larger fish post-transfer. Available vaccines can protect against IPN and good results are obtained by optimizing husbandry and biosecurity measures.

Pancreas Disease (PD): PD is caused by the Salmonid Alphavirus and is present in Europe. It is a contagious virus that can cause reduced appetite, muscle and pancreas lesions, lethargy, and if not appropriately managed, elevated mortality. PD only affects Atlantic salmon in seawater and control is achieved mainly by management and mitigation practices.

Heart and Skeletal Muscle Inflammation (HSMI): HSMI is currently reported in Norway. Symptoms of HSMI are reduced appetite, abnormal behaviour and in most cases low mortality. HSMI generally affects fish the first year in seawater and control is achieved mainly by good husbandry and management practices.

Infectious Salmon Anaemia (ISA): ISA is caused by the ISA virus and is widely reported. It is a contagious disease that causes lethargy, anaemia and may lead to significant mortality in seawater, if not appropriately managed. Control of an ISA outbreak is achieved through culling / harvesting of affected fish in addition to other biosecurity and mitigation measures. Vaccines are available and in use where ISA is regarded to represent a significant risk.

Salmonid Rickettsial Septicaemia (SRS): SRS is caused by an intracellular bacterium. It occurs mainly in Chile, but is also observed, to a much lesser extent, in Norway. It causes lethargy, appetite loss and can result in elevated mortality. SRS is controlled by vaccination, but medicinal intervention (licensed antibiotics) may also be required.

Gill Disease (GD): GD is a general term used to describe gill conditions occurring in seawater. The changes may be caused by different infectious agents; amoeba, virus or bacteria, as well as environmental factors including algae or jelly-fish blooms. Little is known about the cause of many of the gill conditions and to what extent infectious or environmental factors are primary or secondary causes of disease.

Sea lice: Sea lice, of which there are several species, are natural occurring seawater parasites. They can infect the salmon skin and if not controlled they can cause lesions and secondary infection. Sea lice are controlled through good husbandry and management practices, cleaner fish (different wrasse species, eating parasites off the salmon skin) and when necessary licensed medicines

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