Reacción a "Marine heatwaves cause an annual decline of almost 20% in fish biomass"

I believe this is a methodologically sound and valuable study that provides valuable evidence on how different components of ocean warming affect fish biomass. The work is particularly important because it confirms a message already well supported by the literature: chronic ocean warming is associated with persistent declines in biomass.

These results are consistent with existing physiological knowledge. Rising ocean temperatures and their associated effects (such as reduced dissolved oxygen, stratification, and changes in productivity) have well-documented impacts on the metabolism, growth, and reproductive success of many marine species.

That said, there are important nuances that require further investigation. Changes in observed biomass may reflect not only actual variations in abundance, but also spatial redistributions of populations across their range, a process widely documented in warming marine systems. Distinguishing between displacement and net changes in biomass will remain a key scientific challenge, and I believe the spatial modelling tools exist to attempt to predict these distributional shifts.

It is positive and rigorous that the authors themselves acknowledge that ‘fully disentangling the impacts of fishing from those of climate drivers is beyond the scope of this study.’ At the same time, it underscores the need to avoid a simplistic narrative that attributes biomass changes exclusively to climate change. Although this is not the authors' objective, there is a risk, in my opinion, that climate change will become the main explanation for changes in marine species biomass, leaving aside overfishing. Historically, overfishing has been the main determinant of biomass declines in many fisheries around the world. According to the FAO, the proportion of overexploited stocks globally continues to increase, indicating that fishing pressure remains a dominant risk factor. The current challenge is that this overfishing crisis is being further exacerbated by ocean warming and deoxygenation.

In terms of public policy, the study is highly relevant because it emphasises that fisheries management systems must become more climate-adaptive. I agree with the authors that there is a real risk of overexploiting temporary increases in biomass associated with warm events if catch limits do not explicitly incorporate climate variability. However, any management reform must simultaneously address both drivers of change: climate and fisheries. Adjusting quotas solely on the basis of climate without reducing overcapacity and the impact of high-impact gear, such as bottom trawling, is likely to be insufficient to recover stocks.

In conclusion, I believe this study represents an important contribution to advancing more dynamic, ecosystem-based approaches to fisheries management in a changing ocean. Its results should be interpreted within the broader context of the global overfishing crisis, which remains and will likely continue to be a determining factor in the health of marine populations in an increasingly warmer and less oxygenated ocean.