Dynamics of the floodplain fisheries of the Zambezi and Chobe floodplain, Zambezi region, Namibia
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Date
2019
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University of Namibia
Abstract
Floodplain fisheries are typically multi-species and in most cases harvested with a variety of gears. In the upper- Zambezi, artisanal gillnet fishers mainly target three cichlids: Oreochromis andersonii, Oreochromis macrochir and Coptodon rendalli. However, their abundance is declining because of increased fishing pressure and their stocks are becoming vulnerable to overfishing. The principal aim of this PhD thesis was to assess the fish population dynamics in a highly variable system and the implications of these dynamics to fisheries management by investigating the response of floodplain fisheries to water flow and to determine fish harvesting patterns and catch rates on the Zambezi/Chobe floodplain. The specific objectives of this study were: (1) to link littoral fish colonization rates with water quality and water level in floodplain littoral habitats; (2) to determine the feeding ecology of Hydrocynus vittatus (Tigerfish) in the Zambezi/Chobe floodplain (3) to assess the fishing patterns and harvesting rates of the gillnet fishery on the Zambezi/Chobe floodplain; (4) determine the volume and turnover of fish exports from the Zambezi/Chobe floodplain and finally (5) to assess the significance of fish protected areas in protecting the fish stocks of the Zambezi/Chobe floodplains. Seine net surveys showed that the marginal zone of the Zambezi/Chobe floodplain were dominated by fishes of the fish families Cichlidae, Cyprinidae and Characidae. Individual fish densities of small fishes showed spatiotemporal variations among the different stages of flooding with a marked increase in juvenile cichlids during the peak flooding phase while cyprinids were most abundant during the receding (fall) phase. Among other environmental filters, dissolved oxygen and water level had a marked influence on the distribution and abundance of the littoral fish species. The feeding ecology of Hydrocynus vittatus (Tigerfish) (Characidae), in the Zambezi River was investigated between February - December 2016. The findings indicated that large size classes of H. vittatus (>176mm) were largely piscivorous, and showed a diet shift with change in size. The small size classes (<140mm) consumed mainly aquatic insects (21.1%), Synodontis spp. (17.8%), and Micralestes acutidens (12.1%). They later shifted to a diet in which Synodontis spp. (26.1%), Brycinus lateralis (15.2%) and M. acutidens (13.0%) dominated. The study showed that H. vittatus plays an ecological role with the ability of converting un-exploitable non-commercial species such as B. lateralis (15.2%) M. acutidens and Synodontis spp. into exploitable protein. Hence, the population of Hydrocynus vittatus must be of conservation priority to sustain a balanced fishery in the Zambezi River. The fishery on the Zambezi/Chobe floodplain was investigated by means of Catch Assessment Surveys (CAS) from 2010 to 2017. The fishery is dominated by gillnets in the form of monofilament net types. The principal species in gillnet catches were three cichlids: O. andersonii, O. macrochir and C. rendalli. Length at maximum selectivity for the three cichlids showed that they were caught at a length close to their reported length at 50% maturity, raising the fear, risk of growth overfishing. Analysis of annual catch rates of the three commercially important species; O. andesonii, O. macrochir and C. rendalli showed a significant decline from 2010 to 2017. Annual production from the 1700 km2 of the Zambezi/Chobe floodplain was estimated at 2248 t/yr in 2010 dropping to 939 t/yr in 2017. A survey on the floodplain fish processing and exports was conducted at Wenela Border Post, north of Katima Mulilo. Daily fish loads destined for exports were weighed and recorded using a hanging scale at Wenela Border. The study showed that women are the key players in the fish processing and preservation on the Zambezi/Chobe floodplain. The major processing techniques employed by the fish vendors were sun drying and smoking. Approximately 1575.8 t/yr of fish products worth N$22 million were exported to foreign markets in Zambia between June 2015 and December 2016. The active involvement of women in the fish processing and export on the Zambezi/Chobe floodplain as well as the large markets available (both local and foreign) suggest that this sector has the potential to contribute immensely to improving the economic and livelihood of the Zambezi Region. However, the fish vendors faced challenges of inadequate cold storage facilities, poor weather and packaging. Thus, the study recommended private and government’s intervention in the provision of storage facilities and training programs for the fish processors in hygienic handling of fish products, quality control and packaging of processed fish products to conform to human health standards. The fisheries of the Zambezi/Chobe River and its associated floodplains are currently threatened by an increase in fishing pressure. With increasing fishing pressure, fish populations may undergo a series of changes in size, species composition and abundance. As a result, two Fish Protected Areas (FPA) on the Zambezi/Chobe River (Kalimbeza Channel and Kasaya Channel) were recently established to protect and conserve the fish stocks of the Zambezi/Chobe River. However, accrued benefits from these FPAs have not been assessed. Comparative experiments using gillnets of a graded set of mesh sizes (12 mm -150 mm) were conducted between FPA (Kalimbeza channel) and non-FPA (Hippo channel) between March and December 2016 to test the hypothesis that FPA yield high fish abundance (CPUE) than non- FPA. Experimental fishing trials showed higher CPUE by weight and number (p < 0.05) of the five dominant species (H. vittatus, Schilbe intermedius, Pharyngochromis acuticeps, M. acutidens and B. lateralis) in the FPA than non-FPA. The study confirmed the importance of the protected areas in conserving fish resources in the Zambezi/Chobe River. Recommendations were made to manage the fish stocks of the Zambezi/Chobe Rivers by imposing restrictions on gear type, establish more fish reserves and advocate for community engagement in managing their own resources under strict guidance from government.
Description
A dissertation submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy in Science (Biological Sciences)
Keywords
Floodplain fisheries, Zambezi river, Chobe river