Sir

Your News story “Climate findings let fishermen off the hook” (Nature 428, 4; 200410.1038/428004a) offers the view that climate warming and other environmental changes may be just as important as overfishing in driving worldwide declines of fish stocks. It also suggests that climate may be responsible when depleted stocks fail to recover, and that fishery management and climate research should be more closely tied to each other.

While it has been known for many years that climate variability can affect fish recruitment (the replenishment of stocks with juveniles), especially at the margins of species' ranges, there is at present no evidence that worldwide declines are linked in any major way to climate change. Large declines in marine fish communities have always coincided precisely with the onset of industrialized fishing (see R. A. Myers & B. Worm, Nature 423, 280–283; 2003), which occurred at different times in different regions. Likewise, historical declines of marine megafauna, such as large groundfish, turtles or mammals, have always been related to the introduction of new fishing techniques and increased exploitation by European colonists (J. B. C. Jackson et al. Science 293, 629–637; 2001), not to climate change.

Spectacular collapses such as those of Eastern Canadian cod stocks, which at first were attributed to climate change, turned out on closer analysis to be solely related to overfishing (R. A. Myers et al. Ecol. Appl. 7, 91–106; 1997).

We emphasize that heavily overfished stocks may be more sensitive to climate variability, because loss of diversity among locally adapted populations has impaired resilience. Indeed, these findings do not let fishermen (or fishery managers) “off the hook”, but underline the need for more conservative management.

The abundance of spawning and juvenile fish is estimated for most commercial fisheries each year using scientific surveys and fisheries data. This information already integrates actual climate influences and can thus be used to determine optimal fishing quotas.

The problem is that scientific recommendations are almost always exceeded, and overfishing is allowed to continue unabated, despite better knowledge. This problem is a political one. There is already sufficient information available to manage global fisheries sustainably, with or without any additional understanding of climate change.