​​​​​​​Some fish species, particularly migratory species, will shift their biogeographic location to mitigate the effects of climate change. This shift to more favourable environments is also observed in species with fast life cycles, and the abundance of individuals inhabiting those areas will increase, leading to a net geographical displacement. Many other species, however, are not able to track suitable conditions rapidly enough.

Another adaptive strategy can be phenotypic plasticity, where individuals' phenotype will respond to environmental variability within their lifetime. This can mitigate the effects of climate change on a short, intragenerational, time-scale.

Varying phenotypic traits can also be essential to the population regulation of harvested fish species. Somatic growth-rate will influence body size as well as processes such as competition for food, size-dependent fecundity, and/or exploitation rate due to interaction with gear size-selectivity. This will alter stock productivity and recruitment, with potentially important consequences for stock assessment and management.

On an intergenerational time-scale, environmental changes may lead to adaptive evolutionary responses to the natural selection pressures they generate. This accelerates phenotypic change already initiated through phenotypic plasticity, which in turn can facilitate persistence in new environmental conditions.

If conditions stabilize after some change, organisms' phenotypes will be able to adapt to these through plasticity and/or evolutionary response. But climate change, for example, is ongoing so environmental conditions are a moving target. The capacity for organisms to produce an adequate adaptive evolutionary response to new environmental contexts is therefore reduced.

An added complexity is that there is clear evidence showing that fishing activity modifies both heritable life-history traits, and ecological processes in harvested populations, by inducing both phenotypically plastic- and adaptive evolutionary changes.

Ecological and evolutionary changes are closely linked and can occur on the same time-scale, generating eco-evolutionary dynamics. Anthropogenic factors such as climate change and fishing are also co-occurring. They affect fish population dynamics and cause changes in life-history traits that must be addressed. While fisheries commonly target the adult component of the population, environmental changes may affect the whole life cycle. In order to fully understand species adaptation to both environmental change and to fisheries, the whole life cycle must be considered. This requires a complex set of strategies within the context of eco-evolutionary dynamics.

The varying ability of different species to respond to environmental stressors affects fisheries management. A fish populations' adaptive processes affect its resilience and sustainability, due to shifts in stock productivity, life cycle, and species composition in a given ecosystem.

Theme session L will review advances in our understanding of fish life-history tactics and strategies in response to rapid environmental changes. Developments in observation, monitoring, and quantifying methodologies will be discussed, as well as the implications of life history shifts for fish stock assessment, advice, and management.

​Three main topics will be addressed: 

• Research on fish population life-history responses to environmental change; evidence of phenotypic plasticity and evolutionary change, with any implications on population fitness
  
• ​How adaptive responses (or lack of) to environmental change influence exploited fish populations; implications on stock assessment models, projections, and advice
  
• Which harvest control rules could sustain population resilience and fitness, while avoiding unwanted adaptive changes