Productivity and Resilience Enhancement of Exploited Fish stocks: an experimental approach

Worldwide, many fish stocks are in a state of serious decline or collapse due to chronic overexploitation. This incurs severe economic costs with ramifications to ecosystem function and services. For instance, it was shown in the eastern Scotian Shelf ecosystem off Nova Scotia (Canada) that collapse and failure to recover in Atlantic cod (Gadus morhua) induced a trophic cascade in which forage fish density increased, resulting in reduced zooplankton densities and increased algal concentrations. We argue that many of these problems arise because of an opposition between fisheries-induced selection that targets fast-growing and large-sized individuals through the use of minimum-size limits, and natural selection that favours the same large individuals. Instead, fisheries should act in concert with natural selection by selectively harvesting small-sized individuals through the use of maximum size limits. We predict that such a reverse-fishing regime should increase both the productivity and resilience of exploited stocks, and alleviate fishing-induced trophic cascades by preserving large-sized individuals that have disproportionately large predatory effects. REEF is testing this general hypothesis using an artificial selection against or for a large body size on medaka (Orizias latipes) in the laboratory. We are measuring the effects of this bidirectional selection mimicking classical vs. reversed fishing regimes on medaka genetic makeup, productivity and resilience under both laboratory-controlled and natural conditions. We have shown that size selection impacts behaviour and life history, and that these effects depend upon fish sex and availability of feed. Size selection therefore indirectly affects the rest of the food chain and ecosystem. In addition, we have shown that the endocrinological mechanisms affecting growth and reproduction (life history) are affected. We are currently preparing a paper in which we describe how various phenotypic traits are affected by the combination of size selection and environmental changes (temperature and light). We believe that our results provide important insight towards restoring marine ecosystems to their historical state, when top predators were larger and more numerous than today.

Physiology: the discovery of several major, previously unknown mechanisms in cell types mediating encodrine signalling. Developmental biology: a description of all the cell types of the teleost pituitary gland, including the unexpected discovery of two distinct cell types producing the hormone prolactin. Evolutionary biology: the characterization of the interaction between natural and anthropogenic selection in shaping fish genotypes and phenotypes. Ecology: the demonstration of interactions between fishing-induced pace-of-life-syndrome and cascading trophic interactions, highlighting the interactions between evolutionary adaptation and environmental conditions for ecosystems functioning. Bioinformatics: a strategy for integrating scRNA-seq cellular profiles and developmental dynamics during sexual maturation. Societal impact: the results form a scientific basis for the formulation of more sustainable fishing regimes, and ultimately on ecosystem function and productivity.

Worldwide, many fish stocks are in a state of serious decline or collapse. Additionally, collapsed stocks often fail to recover, even when the fishing effort is relaxed. This chronic overexploitation incurs severe economic costs and have ramifications to ecosystem function and services. We argue that many of these problems arise because of an opposition between fisheries-induced selection, that targets fast-growing and large-sized individuals through the use of minimum-size limits, and natural selection that favours the same individuals. Instead, fisheries should act in concert with natural selection by selectively harvesting small-sized individuals through the use of maximum size limits. We predict that such a reverse-fishing regime should increase both the productivity and resilience of exploited stocks. To test this general hypothesis, REEF proposes to use an experimental approach to specifically explore (i) how the classical vs. reversed fishing regimes drive changes in phenotypes and in the underlying molecular architectures that support trait evolvability, (ii) quantify whether and how phenotypic and molecular evolution caused by fishing have cascading effects into the food-web down to algae and, from there, on water quality and the carbon biological pump, (iii) whether and how fishing may change natural selection acting on exploited fish stocks. If successful, reverse fishing regulations will ultimately foster progress towards a restoration of marine ecosystems to their historical state, when top predators were larger and more numerous than today.