Fishery Characteristics and Management in the Floodplain Lakes of Tana River delta, Kenya

Tana River delta floodplain is maintained through a dynamic balance revolving around frequency, extent, and flooding duration. These seasonal and annual flooding variations strongly affect the floodplain communities' fisheries and livelihoods. In the delta, fishing is an important traditional source of livelihood, practiced alongside local agrarian livelihoods such as shifting cultivation and livestock keeping. Fishery utilization and management characteristics in the Tana River delta floodplain lakes are not well documented. This study investigated the characteristics and management of small-scale fisheries in the Tana River delta floodplain lakes. Information relating to past flooding events, fishery characteristics, prevailing regulatory regimes, and the impacts of seasonal flooding were collected using field observations. We collected the information at awareness workshops and key informant interviews between June and September 2018, which covers a significant flooding period of that year, and August 2021, a relatively dry period in the delta. We collected the information from communities living around floodplain lakes in Tarassa and Ngao in the southern part of the delta and Tamaso and Lango la Simba areas in the eastern part of the delta. Results indicate that fishery resources are more diverse during flooding (new species recruitment, presence of spawning, breeding, and foraging sites). The community does fishing all year round, and some part-time practice fishing to supplement shifting cultivation and dry season grazing that are greatly affected by periodic flooding. Floods were crucial in enriching floodplain lakes with diverse fish species. Women are involved in fish trading, acquiring fish primarily within their lineage. Fish is mainly sold in local markets due to poor preservation leading to low-value addition. This study recommends a comprehensive value chain analysis to improve it. Fishing communities around the villages are also most vulnerable to climate change because fishery resource governance needs strengthening, and most households are not involved in resource management. Besides, fishers have limited livelihood options due to lacking skills, technologies, and knowledge to undertake climate adaptation-related decisions. We recommend desilting floodplain lakes and improving connectivity with the main river channel. Additionally, an urgent need is to institute a co-management system to bring together different user groups around these floodplain lakes. Keywords: Fisheries, Flooding, Livelihoods, Floodplain lakes, Governance, Tana River delta DOI: 10.7176/JEES/13-2-02 Publication date:March 31st 202

Sympatric and allopatric Alcolapia soda lake cichlid species show similar levels of assortative mating

Characterizing reproductive barriers such as mating preferences within rapid evolutionary radiations is crucial for understanding the early stages of speciation. Cichlid fishes are well-known for their adaptive radiations and capacity for rapid speciation and as such we investigate assortative mating among Alcolapia species; a recent (<10,000 years), small adaptive radiation, endemic to the extreme soda lakes, Magadi (one species) and Natron (three species), in East Africa. In seminatural aquarium conditions, we observed both courtship and mate choice (tested by microsatellite paternity analysis) to be significantly assortative among the three sympatric Natron species in a three-way choice experiment. This was also the case between allopatric species from Natron and Magadi, as found in a two-way choice experiment. However, the proportion of disassortative matings was substantial in both of these experiments, with hybrids comprising 29% of offspring in sympatric species and 11.4% in allopatric species comparisons. Previous work suggests that the Natron/Magadi split might not be much older than the radiation within Natron, so the similar rate of hybridization in the allopatric comparison is surprising and inconsistent with predictions of reinforcement theory, which predicts a faster rate of accumulation of premating isolation in sympatry. The relatively weak assortative mating in sympatry suggests that additional reproductive barriers, such as microhabitat preferences or spatial structuring may contribute to genetic isolation in nature

Guest Editorial: Contemporary Evolution of African Floodplains and Deltas

International audienc

Molecular phylogenetic analysis of the catfish species Auchenoglanis occidentalis (Valenciennes, 1840) (Pisces: Claroteidae) from Lake Turkana in East Africa: taxonomic implications

Cytochrome c oxidase subunit I (COI) gene sequences of two specimens here recognized as Auchenoglanis occidentalis from Lake Turkana in the Ethiopian section were determined. A COI gene-based phylogenetic analysis was performed for these along with sequences of African catfish species from the family Clarotidae available in GenBank. Based on results of this analysis, it is concluded that (1) the currently identified A. occidentalis is a species complex that includes several distinct species; (2) the Niger River basin harbors two distinct species of Auchenoglanis, one of which occurs in Lake Turkana, as well as A. biscutatus; and (3) A. sacchii is likely a valid species, but it is not the endemic species of Lake Turkana. It is suggested here that species diversity of Auchenoglanis requires further study based on molecular and morphological evidence

Seasonality in diet and feeding habits of the endemic Chala tilapia (Oreochromis hunteri) and two introduced tilapiine cichlids in Lake Chala, East Africa

Oreochromiscf.korogweandCoptodon rendalli, two tilapiine fishes introduced to Lake Chala (Kenya/Tanzania) similar to 40 years ago, may negatively affect the endemic Chala tilapia (Oreochromis hunteri) by competition for food. However, the actual threat posed by the introduced cichlids cannot be assessed without data on the local feeding habits of all three species. This paper describes the diet of O. hunteri and both introduced species, focusing on seasonal changes in food-source availability. Microscopic analysis of gut content in 35 fishes collected over a 20-month period was compared with the composition of littoral food sources and seasonal variation in the limnetic phytoplankton and complemented with exploratory stable-isotope analysis of fish tissue. We found that all three tilapiines in Lake Chala are herbivorous, and during most of the year, they feed on algae and organic detritus on and between rocks in the littoral zone. However, in July-September they migrate to open water to feed on blooming phytoplankton. Interspecific differences in gut content and stable-isotope composition suggest that O. hunteri may have a competitive advantage over the two newcomers by making better use of this seasonal extra food resource. However, this advantage may erode when continuing climate change starts affecting the bloom's predictability

Species integrity and origin of Oreochromis hunteri (Pisces: Cichlidae), endemic to crater Lake Chala (Kenya–Tanzania)

Extensive transfer of tilapia between lakes throughout East Africa has often led to hybridisation with indigenous fish populations. The endemic Oreochromis hunteri of Lake Chala, an isolated crater lake near Mount Kilimanjaro, is potentially susceptible to introgression from a species formerly identified as Oreochromis korogwe, introduced ~ 30 years ago. We combined whole-body geometric morphometry on 104 specimens of both taxa with molecular phylogenetic analysis of mitochondrial loci from 15 O. hunteri and 9 O. cf. korogwe specimens to assess whether hybridisation has occurred. Using fishes from Lake Jipe and Nyumba ya Mungu reservoir, we expanded our analysis to all four Oreochromis species currently inhabiting the Upper Pangani River system to determine the closest relative of O. hunteri, and hence the possible source population of the ancestral species that colonised Lake Chala. Our results indicate no interbreeding occurs between O. hunteri and O. cf. korogwe, and suggest O. jipe to be the closest living relative of O. hunteri. The introduced O. cf. korogwe is a phenotypically uniform but genetically variable population, the identity of which remains unknown. The high haplotype diversity of O. hunteri is consistent with fossil evidence indicating that its ancestor colonised Lake Chala at least 25,000 years ago

Fish-based farming systems: maintaining ecosystem health and flexible livelihood portfolios (chapitre 11)

International audienceThe fish-based farming system encompasses mixed fishing/farming households that derive from 30 to 50 per cent of their income from fisheries and engage in a wider livelihood portfolio including forestry, livestock production, hunting and gathering. It covers a range of ecosystems, climatic zones and sociopolitical contexts. The majority of rural households in the system engage in small-scale fishing, especially young men using canoes and gill nets, but women and children also operate on foot. Fisheries can still be regulated by traditional institutions, but the trends are towards ineffective, state-based regulation or free-for-all situations. Externally financed, larger-scale operations at greater distances from the farm are on the rise.Fishery productivity is largely dependent on the flood pulse linked to seasonal rainfall patterns. Deforestation, land degradation and weather extremes are creating unfavourable, sharper and shorter flood peaks. River regulation by dams decreases system extent and productivity. Trends are towards declining recession agriculture, pasture production and fish reproduction. Large-scale irrigation systems tend to replace the system and exclude its original beneficiaries.Understanding of the system’s functional requirements and its wide-ranging benefits is scanty in both government and development agencies, and thus some pessimism about its future is justified. Emphasis has been on extracting more from the system through industrialisation and upscaling, including for export, but failures are rife. Less attention has been directed to maintaining and enhancing system productivity through ecosystem management interventions, and facilitating the small-scale fisher-farmer’s operations through co-management. The absence of an enabling environment and heavy local taxation favours self-sufficiency rather than marketing.Maintenance of the structural and functional integrity of the wetland ecosystems should be a key focus, especially maintaining the flood pulse, including through managed flood releases from dams. Co-management, based on traditional governance systems, has a better chance of effectively banning destructive techniques and safeguarding nursery areas and reproductive seasons. There is a need for jointly analysed and agreed interventions, more flexible mesh-size regulations suited to local conditions, irrigation systems designed to add to the natural system, and maintenance of input-effective recession agriculture and other flood-based biodiversity, ecosystems and livelihoods. Given climate change uncertainties, planning must include wide error margins for floodplain infrastructure.Aquaculture production is rapidly expanding. The introduction of inappropriate species should be avoided. Emphasis should be on fish that are low in the food chain (e.g. tilapia) and also on the preservation of the natural systems and existing water bodies. Small-scale testing, incremental technological improvements and household level roll-out may be the more sustainable and equitable approach. Culture of the ubiquitous, oil-rich and nutritious catfish Clarias gariepinus, which survives in almost any habitat and is the perfect fish to be smoked, offers opportunities using simple village ponds seeded from the wild.Much can be learned from projects initiated by non-governmental organisations, but interventions should preferably be embedded in local government and operate over medium-scale timeframes. Support through holistic (non-sectoral) and non-dogmatic rural extension workers with a thorough understanding of the local context should be prioritised. Options for governance reform determined via multi-stakeholder dialogue and considering evidence, livelihood security, human rights and cross-sectoral and cross-scale interactions need to be explored

Recurrent changes in cichlid dentition linked to climate‐driven lake‐level fluctuations

International audienc

Morphological variations of wild populations of Nile tilapia (Oreochromis niloticus) living in extreme environmental conditions in the Kenyan Rift-Valley

International audienc