Cooperative Fish and Wildlife Research Units Program: Utah
Education, Research and Technical Assistance for Managing Our Natural Resources

Solokas, M., Z. Feiner, R. Al-Chokhachy, P. Budy, J. Tyrell DeWeber, J. Sarvala, G.G. Sass, S.A. Tolentino, T. Walsworth, and O.P. Jensen. 2023. Shrinking body size and climate warming: Many freshwater salmonids do not follow the rule. Global Change Biology 2023;29:2478–2492. USGS FSP under Al-Chockhachy, IP-146706.


Declining body size is believed to be a universal response to climate warming andhas been documented in numerous studies of marine and anadromous fishes. TheSalmonidae are a family of coldwater fishes considered to be among the most sensitivespecies to climate warming; however, whether the shrinking body size responseholds true for freshwater salmonids has yet to be examined at a broad spatial scale.We compiled observations of individual fish lengths from long-termsurveys acrossthe Northern Hemisphere for 12 species of freshwater salmonids and used linearmixed models to test for spatial and temporal trends in body size (fish length) spanningrecent decades. Contrary to expectations, we found a significant increase in lengthoverall but with high variability in trends among populations and species. More thantwo-thirdsof the populations we examined increased in length over time. Secondaryregressions revealed larger-bodiedpopulations are experiencing greater increases inlength than smaller-bodiedpopulations. Mean water temperature was weakly predictiveof changes in body length but overall minimal influences of environmentalvariables suggest that it is difficult to predict an organism's response to changingtemperatures by solely looking at climatic factors. Our results suggest that decliningbody size is not universal, and the response of fishes to climate change may be largelyinfluenced by local factors. It is important to know that we cannot assume the effectsof climate change are predictable and negative at a large spatial scale.