Methodological inconsistencies define thermal bottlenecks in fish life cycle: a comment on Dahlke et al. 2020

Comparative analyses require researchers to not only ensure data quality, but to also make prudent and justifiable assumptions about data comparability. A failure to do so can lead to unreliable conclusions. As a case in point, we comment on a study that estimated the vulnerability of the world’s fish species to climate change using comparisons between life stages (Dahlke et al. 2020, Science 369: 65–70). We highlight concerns with the data quality and argue that the metrics used to investigate ontogenetic differences in thermal tolerance were incomparable and confounded. Therefore, we recommend caution when interpreting their results in light of climate vulnerability. We suggest potential remedies and recommend thermal tolerance metrics that may be comparable across life stages. We also encourage the creation of guidelines to design, report, and assess comparative analyses to increase their reliability and reproducibility.