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The nature of fisheries- and farming-induced evolution


  • Box 1 The pros and cons of utilizing local vs. nonlocal farmed strains

    A challenge facing the mitigation of the evolutionary effects of fish farming is whether to use (i) local farmed strains derived from wild populations found in the same regions where farming takes place (e.g. ‘A’ in Fig. 2); or (ii) nonlocal strains derived from wild populations not found in the same regions where farming takes place (e.g. ‘B’ or ‘C’ in Fig. 2; see also Bekkevold et al. 2006). Arguments for using either local or nonlocal strains might proceed as follows:

    • ‘Local’: local strains would be less divergent from nearby wild populations, so they would pose less severe outbreeding effects when farmed–wild interbreeding occurs than if nonlocal strains were used.

    • ‘Non-local’: but in being less-divergent, local strains would have weaker differences in reproductive behaviour from wild populations, so they might be expected to successfully interbreed with wild fishes at a much higher rate than nonlocal strains. The fitness costs of farmed–wild interbreeding could therefore potentially affect more of the wild population over the short-term and occur more readily in subsequent generations.

    • ‘Local’: nevertheless, reproductive behaviour in fishes is generally not fixed, and no farmed strain has been so thoroughly domesticated that it was unable to breed with wild relatives (Naylor et al. 2005). Thus, interbreeding would still occur with a nonlocal strain, and even if it did not initially affect as much of the wild population as a local strain, the fitness costs might actually be higher in the long term. For instance, new genetic variants in a more divergent, nonlocal strain could be introduced and/or be created through recombination down the generations in the wild population, and this might ultimately supplant the wild genotypes (e.g. Edmands & Timmerman 2003; Campbell et al. 2006; Johansen-Morris & Latta 2006).

    • ‘Non-local’: perhaps, but in another context, implementing the use of nonlocal strains is more economically attractive since it would not require multiple breeding programmes associated with local population characteristics (i.e. one or a few chief farmed strains could be used ubiquitously).

    • ‘Local’: perhaps, but the use of many local strains might maintain greater levels of genetic diversity in the species by reducing overall genetic homogenization, and thus be more likely to maintain viable wild populations and farmed strains in the long term.

Jeffrey A. Hutchings, Fax: (+ 1) (902) 494-3736; E-mail:


Humans have a penchant for unintentionally selecting against that which they desire most. In fishes, unprecedented reductions in abundance have been associated with unprecedented changes in harvesting and aquaculture technologies. Fishing, the predominant cause of fish-population collapses, is increasingly believed to generate evolutionary changes to characters of import to individual fitness, population persistence and levels of sustainable yield. Human-induced genetic change to wild populations can also result from interactions with their domesticated counterparts. Our examination of fisheries- and farming-induced evolution includes factors that may influence the magnitude, rate and reversibility of genetic responses, the potential for shifts in reaction norms and reduced plasticity, loss of genetic variability, outbreeding depression and their demographic consequences to wild fishes. We also suggest management initiatives to mitigate the effects of fisheries- and farming-induced evolution. Ultimately, the question of whether fishing or fish farming can cause evolutionary change is moot. The key issue is whether such change is likely to have negative conservation- or socio-economic consequences. Although the study of human-induced evolution on fishes should continue to include estimates of the magnitude and rate of selection, there is a critical need for research that addresses short- and long-term demographic consequences to population persistence, plasticity, recovery and productivity.