Socioeconomic impacts of Australian redclaw crayfish Cherax quadricarinatus in Lake Kariba

The rapidly spreading Australian red claw crayfish Cherax quadricarinatus in the Zambezi Basin is a cause for concern considering its potential impacts. The assessment of the impacts of C. quadricarinatus is critical for the prioritisation of policy and management actions in Africa where literature on impacts of C. quadricarinatus is generally scant. We quantified the socioeconomic impacts conferred by C. quadricarinatus on artisanal gillnetting fishery in Lake Kariba to validate anecdotal fisher reports regarding crayfish damage to fish catch on static gillnets. From the catch assessments with registered fishers, fish catch composition, catch per unit effort (CPUE), crayfish entangled on gillnets CPUE, damaged fish CPUE, and damaged areas of the fish were recorded. Basin 2 had significantly higher CPUE with respect to fish catch and crayfish, as well as catch damage, compared to other basins. Damage by crayfish on fish was recorded in all the basins except in Basin 5. There was no correlation between number of crayfish bycatch and fish catch damage. The most frequently affected species was Oreochromis niloticus. On all fish species, eyes, guts and the tail were the frequently damaged parts. Due to C. quadricarinatus damage, fishers are losing 212 tonnes per year which translates to US$ 512 352.92 in Lake Kariba. Damage losses are particularly high when the total income per household in the region, which is mainly contributed by fishing, is considered. The lack of damage in Basin 5 is likely due to fishers developing adaptive new techniques which are less likely to be affected by crayfish. This study is the first in Africa to quantify the socio-economic losses due to crayfish in the field, and the first globally to derive observed costs for C. quadricarinatus. Data from this study have huge conservation and management implications, as crayfish threaten food security as well as incur personal losses to fishers via damage-related costs.