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Lookup NU author(s): Dr Ellen Barrowclift-Mahon, Emeritus Professor Per Berggren, Dr Nicholas Dulvy
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
© 2026 The Author(s). Fish and Fisheries published by John Wiley & Sons Ltd. The maximum intrinsic population growth rate, rmax, is a key determinant of sustainable fishing limits and is increasingly used in risk assessments. We previously showed how the rmax of rays and skates (subclass Batoidea) scales with adult body size, temperature (and hence depth) such that smaller-bodied species and those in warmer, shallower waters have greater rmax and, therefore, will be less sensitive to overexploitation. Paradoxically however, warm shallow-water tropical rays have lower rmax than cold deepwater temperate skates, contra to the expectation from metabolic scaling theory. To resolve this paradox, we examine how rmax is related to adult and offspring size (while accounting for temperature and depth) across 85 ray and skate species. Offspring size mediates relationships between rmax, adult body size, temperature and depth. Despite inhabiting warmer, shallower waters, tropical rays generally have larger offspring and lower rmax compared to temperate skates. Our result explains why tropical rays are less resilient to overfishing despite expectations from metabolic theory that tropical species should have faster life histories and therefore higher rmax and greater resilience than temperate species. Although the drivers of large offspring size in tropical rays remain uncertain, we use basic models of temperature- and size-dependent predation to hypothesise that this is due to greater predation risk in shallow tropical waters selecting for increased maternal investment in offspring size via evolution in viviparity and matrotrophy. Our work highlights the complex relationships among life histories and the environment and may help explain global biogeographic patterns of intrinsic sensitivity to exploitation.
Author(s): Barrowclift E, Bigman JS, Digel ED, Berggren P, Dulvy NK
Publication type: Article
Publication status: Published
Journal: Fish and Fisheries
Year: 2026
Pages: Epub ahead of print
Online publication date: 12/05/2026
Acceptance date: 16/04/2026
Date deposited: 26/05/2026
ISSN (print): 1467-2960
ISSN (electronic): 1467-2979
Publisher: John Wiley and Sons Inc.
URL: https://doi.org/10.1111/faf.70091
DOI: 10.1111/faf.70091
Data Access Statement: The datasets supporting this article are available at FigShare (DOI: https://doi.org/10.6084/m9.figshare.20182109). The R code to reproduce these analyses will be available at Github (https://github.com/EBarrowclift/batoid-rmax-offspring-scaling).
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