On Friday California Superior Court Judge Robert Dondero ruled against the state’s attempt to mandate warning signs wherever canned tuna is sold. In a complete dismissal of claims by California Attorney General Bill Lockyer, the judge ruled that virtually all of the mercury traces in tuna are “naturally occurring.” He also decided that tuna cans would be mislabeled under federal law if they included a California mercury warning. The coup de grace in this common-sense victory? The court observed that the amount of mercury in tuna is actually so low that it should be exempt from California’s hyper-precautionary labeling law. We’ve been saying much the same thing on our FishScam.com website, but Judge Dondero’s sober voice is a welcome one in a debate that’s been marked more by hysterics than logical thinking. To read the court’s decision, click here. But be warned: It’s a large file.

As we told the Seattle Post-Intelligencer on Sunday:

With all the over-the-top rhetoric about mercury in fish, this common-sense ruling should finally stop most of the self-appointed food activists from frightening consumers. Scientifically challenged environmental activists and litigation-hungry attorneys have been exaggerating the impact of mercury in fish for years. It’s about time they backed off.

We’re not assuming that groups like Oceana, the Center for Science in the Public Interest, or the Sea Turtle Restoration Project will fold up their tents and abandon the mercury issue, but at least the issue of whether it makes sense to scare American grocery shoppers away from “brain food” has been decided. As the San Francisco Chronicle noted, the court wrote that “the very fact that a warning sign would be posted in stores for a healthy product that the federal government encourages people to eat makes the sign misleading.

Only hours after the verdict was unveiled on Friday, Lockyer hinted that he might file an appeal — and it’s not hard to figure out why. His office is still pursuing a similar lawsuit against grocery stores that dare to sell fresh and frozen fish without skull-and-crossbone labels. The Los Angeles Times notes that he is “evaluating whether to continue that case.” A successful appeal might also clear the way for Lockyer to bully French-fry and potato-chip makers with his pending lawsuit over insignificant amounts of a chemical called acrylamide.

The issues raised in Judge Dondero’s verdict are too rich — and the cast of characters too varied — for us to cover in one day. There’s a former U.S. Secretary of Health and Human Services who decried “misinformation” about a “healthy food” like fish. The decision includes a robust critique of government mercury regulators who based their fish-eating advice on a poorly designed study of people who eat massive amounts of whale meat. There’s even an oft-quoted “expert witness” (one of a handful who helped develop the Environmental Protection Agency’s hyper-restrictive mercury guidelines) accused by the judge of “misleading” the court about scientific studies under penalty of perjury.

Watch this space all week long as we explore how a judge saw through the mercury hype, and how a carping Attorney General ended up gutted and filleted.