Conservation of Atlantic salmon - gene banking: principles and considerations

Live gene banking

Live gene banking can be thought of as analogous to a standard hatchery situation. However, while the hatchery seeks to supplement a stock/river/fishery, the aims of a live gene bank are to conserve the full genetic signature of a population/s using live fish retained in a facility, rather than just produce fish for enhancement purposes (O'Reilly and Doyle 2007). The main purpose of gene banking is to establish a living reservoir of genetic material that could be used for the re-establishment or enhancement of threatened stocks. The preservation of live fish in living gene banks is a measure used for the most seriously threatened salmon stocks that are no longer capable of surviving in their natural habitats before the danger has been mitigated. The key advantage of live gene banks is the ability to restore the full genome of populations of concern, while the challenges related to these banks are the high cost and the specialist skills required for the management of the banks.

Live gene banking can be very successful, when specific stressors can be identified and ameliorated. For example, the Norwegian Gene Bank programme for wild Atlantic salmon utilizes live gene banks as a temporary living reservoir of genetic material for the reestablishment of living stocks threatened by extirpation. Between the establishment of the first live gene bank station in 1989 up to 2021, 68 Atlantic salmon populations have been or are currently part of the program; 32 of which have successfully been re-established after the eradication of the G. salaris parasite from the river system (Bøe et al. 2021). In contrast to this example, in other situations where the stressor cannot be addressed it may not be possible to re-establish the wild populations. This is the case for the Canadian Inner Bay of Fundy live gene banking programme which has been operating for more than 15 years, yet there is little evidence of progress towards the goal of the re-establishment of self-sustaining wild populations in the face of continuing stressor pressures (Fisheries and Oceans Canada 2018). However, without this ongoing gene banking programme the wild stocks would likely be extinct, the prevention of which was also a goal of the programme (Fisheries and Oceans Canada 2019).

Live gene banking does, however, come with inherent costs and risks (O'Reilly and Doyle 2007). While it may be cost-effective to maintain a small number of populations, it is difficult to envisage a cost-effective situation where the aim is to maintain genetic diversity at a large, e.g. national, scale. Further, live gene banking faces the same problems that are inherent with the maintenance of any stock in a hatchery situation including: small population size, inbreeding depression, domestication selection, loss of adaption etc (for more details see Gilbey et al. 2023). Hence, the population in the bank may deviate over time from the original wild population.