Kills of adult herring occurred in 2 locations in the southwestern Bay of Fundy [Canada] in July 1979 during a bloom of the toxic dinoflagellate Gonyaulax excavata. Fish showed the same symptoms as in a herring kill linked to G. excavata toxins in 1976. Herring stomachs contained G. excavata toxins (66-245 .mu.g/100 g guts), the cladoceran Evadne nordmanni and yellow-brown material probably of algal origin. At the time of the kills the zooplankton community was overwhelmingly dominated by E. nordmanni. Bioassays showed the presence of G. excavata toxins in the zooplanktens (18 .mu.g/g wet plankton). Combined with evidence from the 1976 kill in which pteropods were vectors of the toxins and with results from recent field and laboratory studies, these new observations and results showed that G. excavata toxins caused herring kills in nature with planktonic herbivores, E. nordmanni (in this case) acting as vectors and the toxin transfer mechanism was a general phenomenon among herbivorous zooplankton. Similar food chain events may affect finfish in other areas of the world which experience blooms of toxic dinoflagellates.