The piece of evidence that BEST supports the author's claim in the article "Say No to Genetically Engineered Salmon" is:
"Genetically altered salmon is bad for human health, as it contains more chemicals than wild salmon, and it is bad for the environment, as the genetically altered fish are raised in overcrowded, netted ocean pens."
This statement directly addresses concerns regarding both human health and environmental impact, which are likely central to the author's argument against genetically engineered salmon.