Arctic fish experience lower mortality rates than tropical fish, allowing them to postpone reproduction until later in life, when they are larger and can produce more eggs, according to a study by Mariana Álvarez-Noriega of Australia’s Monash University and colleagues, published on May 25 in the open access journal PLOS Biology. This may have implications for the effects of climate change on the sustainability of fish populations.

Organisms face a trade-off when is the best time to reproduce. Fish continue to grow throughout their lives and larger fish tend to produce disproportionately more eggs than smaller fish, so it pays to reproduce later in life. However, fish that mature slowly run the risk of dying before reaching reproductive age.

Therefore, life history theory predicts that the age at which a fish starts reproducing should be influenced by the species’ growth rate and mortality risk. To test this hypothesis, researchers applied an existing mathematical model of life history evolution to published data on weight at birth, growth rate and adult mortality for 47 species of marine fish. They found that tropical fish experience 80% more mortality than arctic fish.

The model predicted that arctic fish would take advantage of their lower mortality risk to maximize the number of offspring they produce by reaching maturity later in life. Published marine fish data confirmed the model’s predictions: Arctic species tend to reproduce significantly later than tropical species, and the number of eggs they produce increases more as body size increases. As a result, arctic fish tend to produce more eggs than tropical fish.

These findings suggest that climate change could be driving shifts in marine fish growth and reproduction, with warmer oceans causing fish to reproduce earlier in life when they are smaller, and as a result produce fewer eggs. This could have a major impact on fish populations and fisheries worldwide, say the authors.

Alvarez-Noriega adds, “We tested predictions from a life-history optimization model with a global dataset of marine fish demographics and found that reductions in mortality at high latitudes result in delayed maturation and a stronger relationship between size and fecundity.”

Magazine reference

  1. Álvarez-Noriega M, White CR, Kozłowski J, Day T, Marshall DJ (2023) Life history optimization drives latitudinal gradients and responses to global marine fish changes. PLoS Biology 21(5): e3002114. DOI: 10.1371/journal.pbio.3002114