Impacts of artisanal fishing on the reproductive biology and population structure of tigerfish (Hydrocynus vittatus) in the Ume Basin of Lake Kariba, Zimbabwe

Abstract

Fisheries studies concerning the related impacts of fishing on the aquatic environment have mostly dealt with industrial fisheries. Concerted large-scale exploitation can lead to stock declines and potentially species extinction. Hydrocynus vittatus is a piscivore and popular recreational fish species that can grow up to 70 cm fork length and weigh up to 15 kg. Hydrocynus vittatus is also a fish of importance in Lake Kariba as local communities along lake shorelines depend on it for both income and food. There is an insufficient understanding of the impacts of artisanal fishing on tigerfish, H. vittatus population parameters and reproductive biology in Lake Kariba. Hence, this study investigated life history traits and population dynamics of H. vittatus in the Ume Basin of Lake Kariba, north-eastern Zimbabwe. Scales were used to estimate the age of tigerfish and the Bertalanffy growth curve used to estimate the growth parameters. A gonadal reproductive stage determination index was used to determine sexual maturity and the logistic growth curve was used to estimate size at 50% sexual maturity (L₅₀). Using the gonadal maturation index, the L₅₀ for males was estimated ranging between 120 and 149 mm. On the other hand, L₅₀ reached between 250 and 299 mm in females. Females had a higher average mean length (335 mm), compared to that of males (289 mm). The length-at-age data from scales had relatively few outliers and moderate scatter. Parameters for the von Bertalanffy growth curve were (L-infinity = 641.5, k = 0.517, t₀ = 3.07). This study highlighted the negative impacts (male-biased sex ratio and small size at maturity) that artisanal gillnet fishing has on the population structure and reproductive potential of tigerfish in the Ume Basin of Lake Kariba. These impacts are a direct result of both legal and illegal fishing activities of the fishers operating in the Ume Basin and based at Musamba Fishing Camp. There is, therefore, an urgent need for the regulatory authority, the Matusadona Conservation Trust, to engage the fishers in developing long-term strategies to reverse the observed unhealthy population status and allow the tigerfish stock to replenish itself.