Ecological and Evolutionary Consequences of Environmental Change and Management Actions for Migrating Fish

Abstract

Migration strategies in fishes comprise a rich, ecologically important, and socioeconomically valuable example of biological diversity. The variation and flexibility in migration is evident between and within individuals, populations, and species, and thereby provides a useful model system that continues to inform how ecological and evolutionary processes mold biodiversity and how biological systems respond to environmental heterogeneity and change. Migrating fishes are targeted by commercial and recreational fishing and impact the functioning of aquatic ecosystems. Sadly, many species of migrating fish are under increasing threat by exploitation, pollution, habitat destruction, dispersal barriers, overfishing, and ongoing climate change that brings modified, novel, more variable and extreme conditions and selection regimes. All this calls for protection, sustainable utilization and adaptive management. However, the situation for migrating fishes is complicated further by actions aimed at mitigating the devastating effects of such threats. Changes in river connectivity associated with removal of dispersal barriers such as dams and construction of fishways, together with compensatory breeding, and supplemental stocking can impact on gene flow and selection. How this in turn affects the dynamics, genetic structure, genetic diversity, evolutionary potential, and viability of spawning migrating fish populations remains largely unknown. In this narrative review we describe and discuss patterns, causes, and consequences of variation and flexibility in fish migration that are scientifically interesting and concern key issues within the framework of evolution and maintenance of biological diversity. We showcase how the evolutionary solutions to key questions that define migrating fish-whether or not to migrate, why to migrate, where to migrate, and when to migrate-may depend on individual characteristics and ecological conditions. We explore links between environmental change and migration strategies, and discuss whether and how threats associated with overexploitation, environmental makeovers, and management actions may differently influence vulnerability of individuals, populations, and species depending on the variation and flexibility of their migration strategies. Our goal is to provide a broad overview of knowledge in this emerging area, spur future research, and development of informed management, and ultimately promote sustainable utilization and protection of migrating fish and their ecosystems.

Diadromous fish modified timing of upstream migration over the last 30 years in France

“…Jonsson et al., 1990; Todd et al., 2012), we recommend avoiding any artificial selection, in order to maintain a genotype and phenotype diversity and promote resiliency to future climate change (e.g. Ellis & Vokoun, 2009; Moore et al., 2010; Tamario et al., 2019). With the same aim of limiting any form of selection, particular attention should be paid to stocking programmes in order to limit as much as possible the selection of individuals (whether during the capture of adults, the artificial reproduction or the juvenile production) (e.g.…”

A large wild salmon stock shows genetic and life history differentiation within, but not between, rivers

“…Such measures targeted on harvest timing have the potential to alter population trajectories and permit conservation or expansion of certain stock subcomponents (Kallio-Nyberg et al 2011;Harvey et al 2017;Erkinaro et al 2019). Furthermore, variation in migration patterns is an important part of the genetic and phenotypic diversity of fish stocks, and thus essential for the resilience of the populations that fisheries depend on (Quinn et al 2016;Jacobson et al 2019;Tamario et al 2019). Conserving the observed life history diversity could therefore be of large benefit for the longterm survival of the Tornio-Kalix salmon stock.…”

“…The long-term sustainability and ecosystem services of fish populations are buffered and enhanced by genetic and life history diversity, through a portfolio effect (Schindler et al 2010). It is therefore important to maintain such diversity by avoiding the depletion of certain subcomponents of fish stocks (Hilborn et al 2003;Hutchinson 2008;Vähä et al 2017;Jacobson et al 2019;Nordahl et al 2019;Tamario et al 2019). Thus, taking within-river population substructure into account can benefit salmon management, even though this can be difficult to achieve in practice (Potter et al 2003).…”

Morpho-Genetic Divergence and Adaptation of Anadromous Hilsa shad (Tenualosa ilisha) Along Their Heterogenic Migratory Habitats

“…Migration of an anadromous fish from marine to freshwater environment incorporates a wide range of lifehistory strategies by which individuals adapt to the selective pressure driven by the different scales of temporal and spatial environmental heterogeneity (reviewed in Bernatchez, 2016). Therefore, anadromous fishes offer good model systems to investigate how the fish cope with and respond to the selective pressure driven by the environmental heterogeneity (Bernatchez, 2016;Tamario et al, 2019). As a short-term response, anadromous fish may acclimate to the changing environmental conditions through phenotypic plasticity, i.e., by expressing special adaptive phenotypes (Bernatchez, 2016).…”

“…As a short-term response, anadromous fish may acclimate to the changing environmental conditions through phenotypic plasticity, i.e., by expressing special adaptive phenotypes (Bernatchez, 2016). However, the long-term and ultimate response to the environmental heterogeneity is to adapt to the existing environmental conditions, which infers evolutionary (genetic) changes in response to the shifting conditions (Bernatchez, 2016;Tamario et al, 2019). In general, the phenotypic discriminations are largely determined by the genetic differences and are affected by the interaction of ecological and evolutionary systems in response to the spatio-temporal heterogenic environmental conditions (Tamario et al, 2019).…”