The biter bit; scavenging behaviour of native freshwater crayfish on the carrion of native and introduced fish predators in Aotearoa-New Zealand

Freshwater crayfish are important prey items for many fish but are themselves opportunistic scavengers of carcasses of predatory fish. In Aotearoa-New Zealand, kōura, the native freshwater crayfish Paranephrops planifrons, a culturally treasured ‘taonga’ species for indigenous Māori, suffer heavy predation from introduced fish. We investigated potential differences in kōura scavenging behaviour towards carrion of a co-evolved native predator, the long-finned eel Anguilla dieffenbachia and a non-native catfish predator, the brown bullhead Ameiurus nebulosus. Laboratory experiments showed kōura readily leave refugia to feed on dead predatory fish, with little discrimination between eel, catfish or marine (control) fish carcasses. There was no difference in kōura consumption rate of different fish and no difference in the calorific assimilation rate between eel and catfish. Our results suggest kōura will scavenge the carcasses of catfish that have died within invaded systems, even if this trophic interaction is not acknowledged in freshwater food web studies. Local catfish eradication programmes result in culls of thousands of catfish annually. These carcasses are currently wasted and we suggest they could be repurposed as a food resource for kōura, particularly in a future conservation-based aquaculture setting. This could help offset negative impacts the invader is currently having on native crayfish populations.