32 research outputs found
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
Chiloglanis brevibarbis Boulenger 1902
<i>Chiloglanis brevibarbis</i> Boulenger 1902 <p> Described from the Tana River basin, <i>Chiloglanis brevibarbis</i> occurs throughout the Athi and Tana River basins in Central Kenya (Fig. 1). This species in found in a variety of habitat types, although it is usually associated with or near flowing water. Most commonly utilized habitats are rocks and small boulders in flowing water, this species is also found near woody debris or exposed roots along the river bank. In the Athi River at Kibwesi, 141 specimens were collected in emergent stands of vegetation in the middle of the sandy channel.</p> <p> <i>Chiloglanis brevibarbis</i> is the only species of <i>Chiloglanis</i> throughout its range except in the Tsavo River and potentially in other streams of the middle Athi. In the Tsavo River this species is sympatric with an undescribed <i>Chiloglanis sp.</i> that is sister to <i>C. deckenii</i> from the Pangani River. <i>Chiloglanis brevibarbis</i> is distinguished from other Kenyan species in having fewer mandibular teeth, exposed length of mandibular teeth greater than row width, and in possessing 4–5 rows of well-developed premaxillary teeth in large ovoid tooth pads (Fig. 6). Morphological variation is observed between Athi and Tana River populations (Fig. 2, also noted in Whitehead 1958) though biotic dispersal events in the upper reaches of the drainages have likely contributed to admixture between the populations resulting in incomplete lineage sorting (Schmidt <i>et al</i>. 2014). Little is known of ecology and life history of this species. Morphometric measurements and meristic counts of <i>C. brevibarbis</i> populations are found in Table 4.</p>Published as part of <i>Schmidt, Ray C., Bart Jr, Henry L. & Nyingi, Wanja Dorothy, 2015, Two new species of African suckermouth catfishes, genus Chiloglanis (Siluriformes: Mochokidae), from Kenya with remarks on other taxa from the area, pp. 45-64 in Zootaxa 4044 (1)</i> on page 60, DOI: 10.11646/zootaxa.4044.1.2, <a href="http://zenodo.org/record/290006">http://zenodo.org/record/290006</a>
Chiloglanis kerioensis Schmidt, Jr & Nyingi, 2015, sp. nov.
<i>Chiloglanis kerioensis</i> sp. nov. <p>Figs. 1, 3; Table 1</p> <p> <i>Chiloglanis</i> spec. “Kerio”— Seegers <i>et al.</i> 2003: 38.</p> <p> <i>Chiloglanis</i> sp. “Kerio River”— Schmidt <i>et al.</i> 2014: 416, 419.</p> <p> <b>Holotype.</b> NMK FW/3959/1, male ALC, 40.3 mm SL; Kenya, Rift Valley Province, Barwessa River (Barwessa Village) near Lake Kamnarok, Georeferenced: 00.63505° N, 35.618126° E; L. De Vos, 4 January 1999.</p> <p> <b>Paratypes.</b> NMK FW/599/1-13, 9 ALC, 32.1–37.6 mm SL; same collection data as holotype.— NMK FW/ 2794/1-6, 6 ALC, 27.4–38.4 mm SL; same collection data as holotype.—TU 204096, 3 ALC, 32.6–35.9 mm SL; same collection data as holotype.— NMK FW/2243/1-24, 21 ALC, 27.6–32.9 mm SL; tissue vouchers: IRES 1514— IRES 1517; Kenya, Rift Valley Province, Kerio Rift near Chebloch Gorge, off Kabernet—Tambach Rd. (C51), 00.45017° N, 35.64670° E, 2011 IRES team, 23 June 2011.—TU 204094, 3 ALC, 29.7–31.1 mm SL; same collection data as NMK FW/2243/1-24.</p> <p> <b>Diagnosis.</b> <i>Chiloglanis kerioensis</i> is distinguished from <i>C. somereni</i> and <i>C. devosi</i> in having fewer mandibular teeth (eight or fewer versus eight or more) and a larger orbit (>4% SL versus <4% SL). <i>Chiloglanis kerioensis</i> is distinguished from <i>C. brevibarbis</i> by longer barbels (maxillary barbels usually>30% HL versus <30% HL, medial mandibular barbels>10% HL versus <9% HL, and lateral mandibular barbels>17% HL versus <15% HL) and in the arrangement of the mandibular teeth (exposed length of teeth not equal to row width versus exposed portion equal or greater than row width in <i>C. brevibarbis</i> populations). <i>Chiloglanis kerioensis</i> differs from <i>C. deckenii</i> in having a longer premaxillary tooth pad (>3% SL versus <3% SL) and longer lower lip (>60% HL versus <55% HL). The species is distinguished from <i>Chiloglanis</i> sp. aff <i>deckenii</i> by the following combination of characters: <i>C. kerioensis</i> has a longer postcleithral process (>9% SL versus <9% SL) and longer lateral mandibular barbels (>15% HL versus>15% HL).</p> <p> <b>Description.</b> Morphometric measurements and meristics for holotype and paratypes of <i>C. kerioensis</i> are summarized in Table 1. Dorsal, lateral, and ventral views (Fig. 3) illustrate body shape, fin shape and placement, oral disc shape and size, and barbel length.</p> <p> A small, relatively deep-bodied <i>Chiloglanis,</i> maximum standard length observed 40.3 mm. Body dorsally depressed anteriorly and laterally compressed posteriorly. Predorsal angled towards snout. Pre-orbital convex. Postdorsal body angled ventrally towards caudal fin. Preanal profile horizontal; postanal sloping dorsally towards caudal fin. Skin with numerous small unculiferous (horny unicellular projections) tubercles, body uniformly covered with higher concentrations of more pronounced tubercles in the head region. Lateral line complete, arising slightly above horizontal to orbit and sloping ventrally to midlateral alongside of body. Urogenital papillae elongate in males; reduced and separated from anus by shallow invagination in females.</p> <p>Head broadly depressed. Gill openings restricted, from level of pectoral fin attachment to middle of eye. Gill membranes broadly united. Occipital-nuchal shield covered and visible through skin. Eyes small, horizontal axis longest, orbit without free margin. Anterior and posterior nares positioned mid-snout length and equidistant. Nares with raised rim, posterior nares with elongated anterior and medial flaps. Mouth inferior, upper and lower lips united to form sucking disc. Oral disc moderate in size, wider than long and covered in papillae. Barbels in three pairs; maxillary barbel originating from posterolateral region of the disc, unbranched, long, reaching 45% of head length. Lateral and medial mandibular barbels moderate, lateral barbels twice the length of medial barbels, incorporated into lower lip and positioned on both sides of prominent midline cleft on the posterior margin of disc.</p> <p>Primary maxillary teeth numerous (36–80), “S” shaped with exposed tips light brown in color, arranged in three rows on oval shaped tooth. Secondary premaxillary teeth fewer in number and scattered on posterior surface of premaxillae. Tertiary teeth small and needle-like, inserted near midline on dorsal edge of toothplate. Mandibular teeth arranged in one to two rows, “S” shaped, grouped near midline. The anterior row (functional row) supporting 6–8 brown tipped sharp teeth.</p> <p>Dorsal fin originates in anterior third of body. Dorsal fin with small spinelet, spine and 6 rays. Dorsal spine short, anterior margins of spine marked with 2 small notches distally, posterior margins smooth. Adipose fin moderate in length, length into SL four to five times; margin convex with a small incision posteriorly. Caudal fin forked with gently pointed lobes, lower lobe slightly longer than upper lobe, count i, 7, 8, i. Anal fin extending beyond adipose fin terminus, count iii, 8. Pelvic fin origin at vertical between dorsal and adipose fin, margins convex, count i, 6. Pectoral fin with slightly curved smooth spine, moderate in length, five to six times into standard length, count i, 8–9. Post cleithral process going into standard length nine to ten times, buried under the skin. No apparent sexual dimorphism in shape or size of fins. Dimorphism of body size apparent with females being the largest specimens collected.</p> <p> <b>Coloration.</b> Live coloration: Body with yellowish-brown ground color with overlying melanophores and gold iridescent flecks alongside of body. Fins yellow to orange. Typical coloration of preserved specimens is shown in Figure 3. In dorsal view, specimens appear medium brown with three light bands. The first lies anterior to the dorsal fin; second and third bands are anterior and posterior to the adipose fin. Lighter spots visible along sides above lateral line. Head uniformly medium brown.</p> <p>In lateral view, specimens have cream-buff ground color with overlying medium brown above lateral line and cream to yellow from lateral line to belly. Three light bands observed from above extend beyond midline. Light spots on sides above and below lateral line, light areas on lateral line extending dorsally. Numerous small black melanophores scattered across sides, more concentrated below lateral line.</p> <p>Ventral surface yellow to cream colored. Small melanophores near origin of pelvic fins and around anal fin. Oral disc and barbels yellow to cream colored.</p> <p> <b>Etymology.</b> The specific epithet refers to the Kerio River, Lake Turkana basin, where the species is believed to be endemic.</p> <p> <b>Distribution.</b> This species is known from two localities in the upper Kerio River system (the type locality on Barwessa River (asterisk, Fig. 1) and in the Kerio River at Chebloch Gorge (cross, Fig. 1)) and is likely endemic to the system. This species was abundant in the medium rapids upstream from the road crossing (Chebloch Gorge) and were aggregated near the larger boulders. It is likely that further sampling efforts within the upper Kerio River system will reveal addition populations.</p> <p>MORPHOMETRICS Holotype Range Mean±%SD Standard length (mm) 40.3 27.4–40.3</p> <p>Head length 29.5 27.6–33.1 30.6±1.3 Head depth (maximum) 18.4 13.8–19.6 16.3±1.5 Body depth at anus 15.4 12.1–19.1 14.4±1.6 Occipital shield width (minimum) 3.6 3.6–4.7 4.2±1.3 Prepectoral length 29.6 28.5–34.1 31.2±1.3 Predorsal length 42.0 40.2–44.5 42.0±1.1 Prepelvic length 56.5 53.3–57.3 55.7±1.4 Preanal length 70.8 67.2–74.9 71.1±1.6 Eye diameter (horizontal) 4.3 3.9–5.3 4.5±0.3 Orbital interspace 7.6 6.9–8.8 7.7±0.5 Snout length 18.9 15.8–20.1 18.4±0.9 Premaxillary tooth-patch width 13.2 12.4–16.0 14.0±0.9 Premaxillary tooth-patch length 3.5 3.0–4.3 3.6±0.3 Mandibular tooth row width 2.1 1.3–2.7 2.4±0.3 Anterior nares interspace 4.5 3.8–5.3 4.7±0.3 Posterior nares interspace 4.4 3.8–5.4 4.7±0.4 Maxillary barbel length 9.8 8.5–13.4 11.7±1.1 Medial mandibular barbel length 3.2 2.5–4.2 3.3±0.4 Lateral mandibular barbel length 6.0 4.5–7.1 5.9±0.5 Mouth width 9.1 8.3–10.3 9.2±0.5 Oral disc width 19.0 18.1–23.0 20.3±1.1 Oral disc length 18.2 17.4–21.4 19.4±1.0 Upper lip length 4.1 3.1–5.2 4.0±0.4 Lower lip length 7.6 6.1–8.7 7.7±0.6 Pectoral-spine length 16.6 16.4–21.4 18.7±1.2 Pectoral-fin length 22.0 19.3–24.7 21.9±1.5 Width at pectoral-fin insertion 24.0 23.0–28.2 25.0±1.0 Length of postcleithral process 11.9 9.3–13.3 10.9±0.9 Pelvic-fin length 14.9 12.4–16.8 14.5±1.0 Depth at dorsal-fin insertion 20.9 14.6–25.0 18.9±2.3 Dorsal-spine length 12.7 12.2–16.1 14.5±1.1 Dorsal-fin length (longest ray) 17.7 16.3–20.4 18.1±1.0 Dorsal-fin base length 10.1 9.9–13.9 11.9±1.0</p> <p> <i>......continued on the next page</i> Meristics</p> <p>Mandibular tooth rows 1,2</p> <p>Mandibular tooth count (total) 6–16; 8* Mandibular tooth count (functional anterior row) 6–8; 8* Mandibular tooth count (posterior replacement row) 1–8; Primary premaxillary teeth (total) 36–80; 56* Pectoral-fin count I, 8*(37); I, 9(6) Pelvic-fin count i, 6*(43) Dorsal-fin count II, 6 (43) Anal-fin count iii, 7(1); iii, 8*(10) Caudal-fin count i, 7, 8, i* (43)</p>Published as part of <i>Schmidt, Ray C., Bart Jr, Henry L. & Nyingi, Wanja Dorothy, 2015, Two new species of African suckermouth catfishes, genus Chiloglanis (Siluriformes: Mochokidae), from Kenya with remarks on other taxa from the area, pp. 45-64 in Zootaxa 4044 (1)</i> on pages 47-51, DOI: 10.11646/zootaxa.4044.1.2, <a href="http://zenodo.org/record/290006">http://zenodo.org/record/290006</a>