Since crayfish eat dead perch and frogs but do not kill them they are

Crayfish are omnivores as well as detritivores which means not only do they eat both plants and consumers they also eat dead and decaying matter. This means they are on trophic level 2 which is a primary consumer which is right above autotrophs (plants) as well as trophic level 3 which are secondary consumers whose diet consists of primary consumers. Finally because its a detritivore it exists in all of the trophic levels because it eats dead matter from each level.