A new study reveals that booming fish stocks in cold waters are misleading, as climate change is causing significant declines in fish populations. For every 0.1°C increase in ocean temperature, fish numbers drop by over 7%. The study distinguishes between gradual warming and sudden marine heatwaves, both of which are harmful. While some fish populations may temporarily thrive during heatwaves, this creates a false sense of security for fisheries managers, who may mistakenly raise quotas. Ultimately, continued ocean warming is expected to reduce fish numbers globally, regardless of the initial gains.