Alloperla Stonefly Nymphs: Predators or Scavengers on Salmon Eggs and Alevins?

Stonefly nymphs have frequently been suspected of being predators or scavengers on salmonid eggs and alevins, and recent studies have particularly emphasized Alloperla nymphs. Live and dead salmon alevins were placed in perforated plastic boxes and buried in spawning riffles of two streams. Most dead alevins disappeared, and more than 50% of the live alevins survived. Nymphs of Alloperla (A. oregonensis and A. borealis) were the most consistently abundant benthic animal in the plastic boxes. Dead eggs and alevins disappeared more rapidly from boxes placed in an area which contained few naturally occurring dead salmon eggs than in areas which contained many. Dead eggs and alevins were eaten, and live eggs and alevins survived when placed in aquaria with Alloperla nymphs. I conclude that the Alloperla nymphs definitely were scavengers and probably not predators on pink salmon eggs and alevins.