Natural mortality: Its ecology, how it shapes fish life histories, and why it may be increased by fishing☆

By C. Jørgensen, R. Holt. 2013

135 citations recorded by the source corpus.

Abstract A stronger focus on natural mortality may be required to better understand contemporary changes in fish life histories and behaviour and their responses to anthropogenic drivers. Firstly, natural mortality is the selection under which fish evolved in the first place, so a theoretical understanding of effects of natural mortality alone is needed. Secondly, due to trade-offs, most organismal functions can only be achieved at some cost in terms of survival. Several trade-offs might need to be analysed simultaneously with effects on natural mortality being a common currency. Thirdly, there is scattered evidence that natural mortality has been increasing, some would say dramatically, in some fished stocks, which begs explanations. Fourthly, natural mortality most often implies transfer of mass and energy from one species to another, and therefore has foodweb and ecosystem consequences. We therefore analyse a model for evolution of fish life histories and behaviour, where state-dependent energy-allocation and growth strategies are found by optimization. Natural mortality is split into five different components, each specified as the outcome of individual traits and ecological trade-offs: a fixed baseline mortality; size-dependent predation; risk-dependent growth strategy; a fixed mortality when sexually mature; and mortality increasing with reproductive investment. The analysis is repeated with and without fishing. Each component of natural mortality has consequences for optimal life history strategies. Beyond earlier models, we show i) how the two types of reproductive mortality sometimes have similar and sometimes contrasting effects on life history evolution, ii) how ecosystem properties such as food availability and predation levels have stronger effects on optimal strategies than changing other mortality components, and iii) how expected changes in risk-dependent growth strategies are highly variable depending on the type of mortality changed.

Subfields: Aquatic Science, Global and Planetary Change, Nature and Landscape Conservation

View Paper: https://www.semanticscholar.org/paper/c328c2dcf025839ff7874612278857a3b9141837

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In Aquatic Science

In Global and Planetary Change

In Nature and Landscape Conservation

Citations in the corpus

Passive gear‐induced timidity syndrome in wild fish populations and its potential ecological and managerial implications (2017, unknown): “Increased boldness is possible too, but these effects seem to be constrained on harvesting being unrelated to size or other traits (Jørgensen and Holt 2013) or strongly focused on juveniles (K. Andersen et al. unpubl. data), both of which are rare in most wild fisheries.”
Trends and management implications of human-influenced life-history changes in marine ectotherms (2016, background): “…mortality due to reproductive changes in 145 behaviour (competition for mates, nest guarding, spawning migrations), reduced feeding, energetic 146 investment in gonads instead of somatic growth, and less energy allocation to immune functions 147 (Jørgensen and Fiksen 2010; Jørgensen and Holt 2013).”
Extreme increases in natural mortality prevent recovery of collapsed fish populations in a Northwest Atlantic ecosystem (2015, background): “The susceptibility of these fishes to predation may also have been further increased by fisheriesinduced life-history and behavioural changes (Jørgensen & Holt 2013).”