Spatial and temporal distribution of an invasive crayfish (Cherax quadricarinatus) in Lake Kariba, Zimbabwe

Abstract

AbstractDetermining the extent of invasion by an aquatic invasive species is the first step to informing effective management strategies. The spatial and temporal distribution of an introduced invasive crayfish (Cherax quadricarinatus) in Lake Kariba, Zimbabwe was investigated to determine the extent of the invasion. Five lakewide surveys across the five basins of the lake (Sanyati; Bumi; Sengwa; Mlibizi; Binga) were conducted between March 2014 and July 2016. Monthly sampling for crayfish and physico‐chemical parameters was done in the Sanyati basin from January to December 2013. Presence/absence data from the lakewide surveys indicated that the crayfish had spread to three of the five basins by July 2016; namely, the Sanyati, Bubi and Sengwa basins. There was a general decrease in the total and average number of crayfish caught with each consecutive lakewide survey. Out of 19 sampled sites in the Sanyati basin, crayfish were found to be present at 16 sites, including both protected and unprotected areas, and in all substrate types (muddy, sandy and rocky substrates). Crayfish catches differed significantly over time (months), with a general increase from January and peaking in July, after which a decrease was observed until September before it steadily increased again in December. Crayfish catches differed significantly among the sites in the Sanyati basin. Temperature and electrical conductivity significantly affected the CPUE of C. quadricarinatus, with an increase in both parameters being associated with a decreased CPUE (p < 0.05; Generalized Linear Mixed Models). The results of the current study indicate C. quadricarinatus is now in the spread stage of the invasion process and is making use of all habitats in the lake. Increased trapping and containment to prevent further spread should be considered as management options.