Fisheries-induced evolution in the wild and in the lab
Mikko Heino
Evidence for fisheries-induced evolution comes from laboratory experiments,
observations from wild fish stocks, and theoretical models. Most field studies have
examined age and size at sexual maturation, mostly because these metrics often suggest
marked changes and because suitable data are often available and allow accounting for
major environmental influences. Until about ten years ago, it was assumed that the
widely documented declining trends in age and size at maturation could be explained
with growth-related phenotypic plasticity, but analyses using the probabilistic
maturation reaction norm approach suggest that this is usually not a sufficient
explanation; instead, the patterns suggest that fisheries-induced evolution plays a
significant role. Evidence for fisheries-induced evolution in other traits have turned out
to be more evasive: there are fewer studies because data availability is worse, and more
often studies end up with ambiguous results. However, theoretical models indicate that
maturation responds to fisheries selection more readily than other life-history traits.
Experimental studies, on the other hand, have tended to focus on other traits than
maturation, often on growth (a trait extensively studied in aquaculture breeding
programmes too). Significant responses can often be observed after just a few
generations of selection, although many studies have been criticized for imposing
artificially strong selection. Importantly, experiments have shown a wide range of
correlated responses to selection, including responses in behavioural and physiological
traits. Taken together, the interpretation of field studies as showing fisheries-induced
evolution is supported by experiments, but experiments are also suggesting that field
studies have only been able to scratch the surface when it comes to the true diversity of
evolutionary responses to fishing.