The population dynamics of a recently introduced crayfish, <i>Cherax quadricarinatus</i> (von Martens, 1868), in the Sanyati Basin of Lake Kariba, Zimbabwe

Abstract

The redclaw crayfish Cherax quadricarinatus is a recent introduction into Lake Kariba, Zimbabwe where it is rapidly spreading. There are, however, no studies that have investigated the population dynamics and possible ecological impacts of the crayfish in the lake. This study investigated aspects of the population biology of C. quadricarinatus in the lake. These included sex distribution, population growth and mortality parameters, probability of capture, recruitment and length at age of ge at maturity. Crayfish were captured monthly between January and December 2013 from 13 sites using opera house bait traps. Aspects of the species population biology were estimated using a fish stock assessment tool, FISAT II. A total of 3 205 crayfish were captured, of which 44% were male, 49% female and 7% intersex individuals. The asymptotic length (L_∞ = 112.88 mm), curvature parameter (k = 0.72), longevity (t_max = 4.17 years), growth performance index (φ = 3.96), total mortality (Z = 2.06 y⁻¹), fishing mortality (F = 1.07 y⁻¹), natural mortality (M = 0.99 y⁻¹), rate of exploitation (E = 0.52) and length-at first capture (L_c = 44.48 mm) were estimated. Fecundity averaged 503 ± 229 eggs female⁻¹ and increased with size (weight and carapace length). Gravid females were found throughout the year but the highest proportion of females with eggs (4–10%) were found in the first quarter, whereas recruitment peaked in May and June. The smallest crayfish with eggs (48.75 mm CL) was estimated to be 1.02 years and the largest (94.82 mm CL) 2.85 years. Cherax quadricarinatus exhibited an r strategy life-history pattern due to continuous reproduction and high fecundity. In Lake Kariba, C. quadricarinatus is now well into the establishment stage of the Introduction–naturalisation–invasion continuum and spreading in the lake. Management options should thus aim at preventing further spread and reducing the population size and the potential negative impacts of this species.

Keywords: fecundity, mortality, recruitment, reproduction, sex distribution