From form to function: Morphology as a proxy for life history and population performance in fish

Life history strategies emerge from trade-offs between growth, survival and reproduction and are key predictors of how populations respond to environmental disturbances. However, estimating these strategies typically requires detailed demographic data, which are unavailable for many species. Morphological traits may provide a practical proxy for life history strategies, offering a scalable approach for data-deficient populations.

We parameterised dynamic energy budget integral projection models for 290 marine and freshwater fish species to quantify life history strategies and measured nine morphological traits from lateral-view photographs for each species. We used phylogenetically corrected principal component analysis to summarise life history strategies and morphological traits, and tested whether morphology predicts life history strategies, and whether either predicts population growth rate or demographic resilience.

Lateral size morphology, comprising body elongation, relative eye size and oral gape position, predicted generation turnover depending on water column position, and predicted reproductive output depending on clade. Generation turnover, reproductive output and lateral size morphology predicted population growth rate and resilience, but population growth rate and resilience were not directly aligned, challenging common assumptions in fisheries management that treat them as interchangeable.

Our results show that morphology can reliably capture key axes of life history strategy and components of population performance. Incorporating morphological proxies into life history frameworks could enable rapid, low-cost assessments of population resilience, extending life history frameworks to species lacking demographic data, and providing actionable insights for fisheries management and conservation under increasing pressures from overfishing, habitat loss, and climate change.