At a live gene bank for wild salmon. Photo: Norwegian Veterinary Institute

Gene banks for wild salmon

Gene banks are an essential tool for maintaining the genetic diversity of Norway’s stocks of wild Atlantic salmon. The Norwegian Envornment Agency  started work on its gene bank programme in 1986.

Norway has two types of gene banks for salmon: 

  • a frozen gene bank
  • three live gene banks

Partners in the gene bank programme

Public authorities, organisations and industry are all involved in work on the gene banks for salmon. In addition to the individual gene banks, the Directorate’s key partners are:

  • hydropower companies
  • Norwegian Veterinary Institute
  • Cryogenetics AS, Geno Hallsteingård

Frozen gene bank for wild salmon

One necessary conservation measure for threatened wild salmon stocks is to collect and store milt (sperm) from wild salmon stocks and cryopreserve this genetic material in a gene bank. This work has been under way since 1986.

Deep-freezing salmon milt makes it possible to preserve genetic material almost indefinitely. Two millilitres of milt – enough to fertilise roughly 3 000 eggs – is collected from each male fish.

Which salmon stocks are selected for preservation?

The aim is to collect milt from wild salmon stocks in different parts of Norway and from a variety of habitats. Stocks under threat of extinction or which are of special scientific value or of high fishing value are given priority.

In this context, salmon from a specific river or major tributary are considered to belong to one stock.

How milt is collected

The target is to collect milt from at least 50 individuals from each stock. Samples are collected over a period of at least two years to minimise the risk of over-representing any one year-class. The milt is stored deep-frozen in liquid nitrogen.

So far, the gene bank contains deep-frozen samples from 169 wild salmon stocks and four trout (Salmo trutta) stocks. The map shows the geographical distribution of these stocks. 

Live gene banks for wild salmon

Live gene banks are used to keep broodstock from salmon stocks that are currently seriously threatened. Norway has three of these live gene banks.

Every wild Norwegian salmon stock has unique genetic traits, which are genetic adaptations to local conditions. Interbreeding with escaped farmed fish may alter the genetic make-up of a local stock, with adverse effects. This makes it important to preserve the genetic material of the individual stocks.

Threats to wild salmon stocks

Live specimens from salmon stocks that cannot currently survive in their native rivers are kept in live gene banks until the situation improves. Threats to wild salmon stocks may include:

  • the ectoparasite Gyrodactylus salaris
  • acid rain
  • interbreeding with escaped farmed fish
  • chronic effects of sea lice from intensive aquaculture
  • hydropower development.

 

Running the live gene banks

The live gene banks either deliver eggs to local facilities that raise fish for stocking programmes, or culture eyed eggs for direct planting in river beds for hatching in the wild. The cultured offspring of broodstock fish are eventually released into their parents’ river of origin.

The broodstock must be kept free of disease. Fish are regularly checked for disease and strict working routines are followed when handling fish and transporting eggs and milt.

All eggs destined for the gene banks are disinfected beforehand. Because seawater is more likely to contain pathogens, the gene banks use fresh water.

To minimise the risk of spreading fish diseases to the rivers, only disinfected eggs are exported to the culturing facilities.

Locations of Norway’s live gene banks

Three regional gene banks for live fish have been established (see map), located in:

  • Eidfjord in Hordaland county (western Norway)
  • Haukvik in Sør-Trøndelag county (central Norway)
  • Bjerka in Nordland county (north Norway)

The Norwegian Environment Agency operates the first two, while the third is run by the power company Statkraft. 

How a gene bank is run

Gene banks preserve important genetic material from Norway’s wild salmon stocks. Here are the practical steps involved in this work.

1. Wild salmon are caught in a river, raised to maturity, then stripped

Fish caught in rivers are raised locally in tanks until they reach sexual maturity, when they are stripped to collect the eggs or milt. Some of the milt is then deep-frozen (at -196°C in liquid nitrogen) and shipped to a central storage facility. The remaining fresh milt and unfertilised eggs are shipped to a live gene bank.

2. Fertilisation

Each female’s eggs are fertilised with milt from a single male, then disinfected and placed in an incubator. The eggs from each female are kept separate throughout this process.

3. Fin-clipping

After hatching, each full-sibling family is kept in a separate tank until the fry are large enough (roughly 7 cm) for fin-clipping (so that family groups can be recognised) in July/August. Next, all families from the same stock are placed together in one tank.

4. Electronic tagging

In their second year of life, the fish approach smolt size (12–24 cm) and 30–200 individuals from each family are individually fitted with an electronic tag.

5. Isolation

For the next two years each generation is kept isolated in separate parts of the facility, which means that each year class is kept separate for a total of four years. This makes it easier to combat any outbreaks of fish diseases at a facility, and also simplifies the task of keeping track of families, year classes and stocks.

6. Merged together by stock

After four years, fish from the oldest year class are placed together, although different stocks are still kept separate. 

Rebuilding salmon stocks and restocking rivers

The main objective of restocking projects is to carry out and document the effective and cost-effective rebuilding of strong year classes of salmon in rivers until spawning stock targets can be achieved through natural reproduction.

The Norwegian Environment Agency uses eyed eggs or fry from the live gene banks to restock rivers. An annual production and reintroduction of one to two million fertilised eggs per stock would not be unusual in situations such as after rotenone treatment of a river system infected by Gyrodactylus salaris.  

Rebuilding stocks is a demanding task

A restocking project for a single river can take five to ten years. In rivers where temporary migration barriers have been erected while G. salaris is being eradicated, no restocking is carried out upstream of the barriers until the river has been declared parasite-free, i.e. after roughly five years, which means that the entire project takes about ten years.

Restocking projects for specific rivers include plans for:

  • rebuilding the local stock
  • the practical details of planting eggs and releasing fish
  • documenting and reporting  survival and population growth of adult fish in the rivers.

Projects are carried out in close cooperation with local interest groups, the public administration and relevant hydropower operators.  

Planting eggs in the river bed

Most biological material is returned to rivers from the live gene banks in the form of eyed eggs. Eggs are incubated under closely controlled and monitored conditions resembling those in the river from which they originate, in order to optimise their development. Egg planting is also the best way of using the genetic material from the gene banks.

Fish and eggs returned to the rivers are marked at the eyed-egg stage. Various methods are employed to assess the effectiveness of restocking, including:

  • marking eggs
  • measuring hatching success
  • counting fry density
  • counting spawning fish
  • monitoring smolt migration to sea

Marking the eggs makes it possible to assess how much of the production in a river originates from the gene bank material. The other methods above are for estimating total production in a river. 

These stocks have been successfully rebuilt and are no longer kept in the live gene banks: 

  • Beiarelva
  • Aureelva
  • Valldalselva
  • Norddalselva
  • Måna
  • Eidsdalselva
  • Fjelna
  • Flekke
  • Lone
  • Oselva

Stocks being rebuilt

Restocking after rotenone treatment has been in progress in the Ranaelva and Røssåga rivers since 2005, and there is now documentation that strong stocks have been established. Once the eradication programme for G. salaris has been completed in the Vefsna (Nordland county’s largest river), the river will be restocked using full-sibling families from the Bjerka gene bank. Egg planting will be the main strategy, but smolt will also be released in the first few years to accelerate the rebuilding process. The Figga, Ogna and Bya rivers are also being restocked. 

A number of salmon stocks are facing  a combination of threats, with complex effects. In some cases, eyed eggs are being planted to replenish the natural but weakened stocks until environmental pressures can be reduced or eliminated.

Stocks that are being replenished:

  • Vosso
  • Jølstra
  • Ekso
  • Årøyelva
  • Eio/Bjoreio

Database for live gene banks

The LGBAS database for live gene banks keeps track of the genealogy of every fish. The “central nervous system” of the gene banks is a specially developed IT system for the live gene banks. Called LGBAS, it is an essential tool for the practical, day-to-day operations of the various gene bank facilities, where data on individual genealogies are vital.

The LGBAS system consists of two components: the database itself and the software. It was initially created in autumn 1998 at the request of the Norwegian Environmetn Agency.

How the IT system works

The LGBAS system communicates with passive electronic tags fitted to every fish. This is an effective and non-intrusive  system which also ensures optimal quality assurance of genealogical data.

Every instance of eggs/milt stripping and fertilisation is recorded in the database in order to document all the genetic material at each facility and any fertilised eggs planted in the rivers.

Genealogies for every individual provide a basis for selecting new crosses to be used in producing eggs and fish for release. At an age of 7–10 years, fish are used to breed new generations of broodstock. Fish are then crossed to maintain the maximum possible familial and individual diversity.

Continual refinement

The IT system keeping track of production at all the gene bank facilities is under constant development. Its software must be tailored for deployment to each new facility.

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