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Igulu M.M.,Radboud University Nijmegen | Igulu M.M.,Tanzania Fisheries Research Institute | Nagelkerken I.,Radboud University Nijmegen | Nagelkerken I.,University of Adelaide | And 3 more authors.
Ecosystems | Year: 2013

Coastal ecosystems are energetically connected through passive transport of nutrients but also by migrations of motile organisms. Mangroves are highly productive tropical ecosystems that replenish offshore populations of many species, but we know little about the degree to which this production is fuelled by prey from mangroves, especially in the cases in which mangroves are only accessible at high tide. Different results have been obtained on the importance of mangroves as feeding habitats, confounded by differences in species composition, seascape configuration, and methodology. In the present study, we took a more holistic approach by exploring reliance by fishes on mangroves as a feeding habitat at multiple ecological levels: from individuals to species to communities in mangrove ecosystems from across the globe, using a stable isotope approach. A two end-member mixing model showed a wide range (12-72%) in degree of reliance on mangrove food sources by fishes from different studies across the globe. However, analyzed at the levels of individual fish and species, reliance was low (for example, <25% for 55% of the species worldwide, or <50% for 85% of species, respectively) even though they were collected from sites that differed in geographical location, tidal regime, seascape structure, and species composition. The high fisheries productivity of mangroves appears to be energetically supported largely by food sources from adjacent habitats. In light of the ongoing rapid demise and fragmentation of mangrove and adjacent ecosystems, loss of ecosystem connectivity is likely to affect the productivity and functioning of tropical coastal ecosystems and the services they provide. © 2013 Springer Science+Business Media New York.


Ngatunga B.P.,Tanzania Fisheries Research Institute
Freshwater Biology | Year: 2016

Genetic differences among freshwater fish populations are dependent on life-history characteristics of the species, including the range of adult dispersal and the extent of homing to natal breeding grounds. However, the effects of variation in such characteristics on population genetic connectivity are rarely studied comparatively among closely related species. We studied population genetic structure within three congeneric cyprinid species from the Lake Malawi catchment that differ substantially in life-history traits and conservation status, using a combination of microsatellite and mitochondrial DNA markers. Mpasa (Opsaridium microlepis) is a large (70 cm total length) migratory species that spawns in rivers, but as an adult is exclusively known from the main lake body. Sanjika (Opsaridium microcephalum), is a medium size (30 cm total length) species that exists in lake breeding, river-lake migratory and apparently landlocked populations. Dwarf sanjika (Opsaridium tweddleorum) is a small non-migratory species (15 cm total length) that persists in small tributaries surrounding the main lake and adjoining rivers. The results revealed striking differences among the three species in spatial genetic structuring. The river-lake migratory mpasa showed only weak yet significant population genetic structure within the main Lake Malawi catchment, suggesting that there is no strong natal homing. The habitat-generalist sanjika showed only weak spatial genetic differentiation at microsatellite loci within the Lake Malawi catchment, but moderate structure in mitochondrial DNA, potentially reflecting male-biased dispersal. The river-restricted dwarf sanjika showed strong genetic structure in both microsatellite and mitochondrial DNA, suggesting strictly limited dispersal at both adult and juvenile stages. We conclude that contrasting migration life histories have resulted in dramatically different patterns of population genetic structure among these congeneric species. The observed patterns demonstrate how divergent life-history evolution may strongly influence broader patterns of population genetic connectivity in freshwater fish, with consequences for management and conservation. Specifically the results suggesting gene flow among Lake Malawi populations of mpasa, an IUCN red-listed 'Endangered' species endemic to the lake catchment, imply that conservation initiatives operating at both local and catchment scales are needed to reverse local population decline. Copyright © 2016 John Wiley & Sons Ltd.


Kimirei I.A.,Radboud University Nijmegen | Kimirei I.A.,Tanzania Fisheries Research Institute | Nagelkerken I.,Radboud University Nijmegen | Nagelkerken I.,University of Adelaide | And 3 more authors.
PLoS ONE | Year: 2013

Mangroves and seagrass beds have long been perceived as important nurseries for many fish species. While there is growing evidence from the Western Atlantic that mangrove habitats are intricately connected to coral reefs through ontogenetic fish migrations, there is an ongoing debate of the value of these coastal ecosystems in the Indo-Pacific. The present study used natural tags, viz. otolith stable carbon and oxygen isotopes, to investigate for the first time the degree to which multiple tropical juvenile habitats subsidize coral reef fish populations in the Indo Pacific (Tanzania). Otoliths of three reef fish species (Lethrinus harak, L. lentjan and Lutjanus fulviflamma) were collected in mangrove, seagrass and coral reef habitats and analyzed for stable isotope ratios in the juvenile and adult otolith zones. δ13C signatures were significantly depleted in the juvenile compared to the adult zones, indicative of different habitat use through ontogeny. Maximum likelihood analysis identified that 82% of adult reef L. harak had resided in either mangrove (29%) or seagrass (53%) or reef (18%) habitats as juveniles. Of adult L. fulviflamma caught from offshore reefs, 99% had passed through mangroves habitats as juveniles. In contrast, L. lentjan adults originated predominantly from coral reefs (65-72%) as opposed to inshore vegetated habitats (28-35%). This study presents conclusive evidence for a nursery role of Indo-Pacific mangrove habitats for reef fish populations. It shows that intertidal habitats that are only temporarily available can form an important juvenile habitat for some species, and that reef fish populations are often replenished by multiple coastal habitats. Maintaining connectivity between inshore vegetated habitats and coral reefs, and conserving habitat mosaics rather than single nursery habitats, is a major priority for the sustainability of various Indo Pacific fish populations. © 2013 Kimirei et al.


Grant
Agency: GTR | Branch: NERC | Program: | Phase: Research Grant | Award Amount: 1.10M | Year: 2015

East Africa (EA) has one of the worlds fastest growing populations, with maxima around water-bodies and rapid urbanisation. Climate change is adding to existing problems increasing vulnerability of the poorest. HyCRISTAL is driven by EA priorities. EA communities rely on rainfall for food via agriculture. EAs inland lakes are rain-fed and provide water, power and fisheries. For EAs growing cities, climate impacts on water resources will affect water supply & treatment. HyCRISTAL will therefore operate in both urban & rural contexts. Change in water availability will be critical for climate-change impacts in EA, but projections are highly uncertain for rain, lakes, rivers and groundwater, and for extremes. EA Long-Rains are observed to be decreasing; while models tend to predict an increase (the EA Climate paradox) although predictions are not consistent. This uncertainty provides a fundamental limit on the utility of climate information to inform policy. HyCRISTAL will therefore make best use of current projections to quantify uncertainty in user-relevant quantities and provide ground-breaking research to understand and reduce the uncertainty that currently limits decision making. HyCRISTAL will work with users to deliver world-leading climate research quantifying uncertainty from natural variability, uncertainty from climate forcings including those previously unassessed, and uncertainty in response to these forcings; including uncertainties from key processes such as convection and land-atmopshere coupling that are misrepresented in global models. Research will deliver new understanding of the mechanisms that drive the uncertainty in projections. HyCRISTAL will use this information to understand trends, when climate-change signals will emerge and provide a process-based expert judgement on projections. Working with policy makers, inter-disciplinary research (hydrology, economics, engineering, social science, ecology and decision-making) will quantify risks for rural & urban livelihoods, quantify climate impacts and provide the necessary tools to use climate information for decision making. HyCRISTAL will work with partners to co-produce research for decision-making on a 5-40 year timescale, demonstrated in 2 main pilots for urban water and policies to enable adaptive climate-smart rural livelihoods. These cover two of three areas of need from the African Ministerial Council on Environments Comprehensive Framework of African Climate Change Programmes. HyCRISTAL has already engaged 12 partners from across EA. HyCRISTALs Advisory Board will provide a mechanism for further growing stakeholder engagement. HyCRISTAL will work with the FCFA global & regional projects and CCKE, sharing methods, tools, user needs, expertise & communication. Uniquely, HyCRISTAL will capitalise on the new LVB-HyNEWS, an African-led consortium, governed by the East African Community, the Lake Victoria Basin Commission and National Meteorological and Hydrological agencies, with the African Ministerial Conference on Meteorology as an observer. HyCRISTAL will build EA capacity directly via collaboration (11 of 25 HyCRISTAL Co-Is are African, with 9 full-time in Africa), including data collection and via targeted workshops and teaching. HyCRISTAL will deliver evidence of impact, with new and deep climate science insights that will far outlast its duration. It will support decisions for climate-resilient infrastructure and livelihoods through application of new understanding in its pilots, with common methodological and infrastructure lessons to promote policy and enable transformational change for impact-at-scale. Using a combination of user-led and science-based management tools, HyCRISTAL will ensure the latest physical science, engineering and social-science yield maximum impacts. HyCRISTAL will deliver outstanding outputs across FCFAs aims; synergies with LVB-HyNEWS will add to these and ensure longevity beyond HyCRISTAL.


Everson I.,Anglia Ruskin University | Taabu-Munyaho A.,National Fisheries Resources Research Institute NaFIRRI | Kayanda R.,Tanzania Fisheries Research Institute
Fisheries Research | Year: 2013

Data from the first series of lakewide fisheries acoustic surveys of Lake Victoria, East Africa, have been re-analysed according to current protocols. Surveys took place in February and August each year between 1999 and 2002. The primary aim has been to estimate the standing stock of Nile perch and dagaa, the main species taken in commercial fisheries on the lake. The results show that over the period of the surveys from 1999 to 2002 there was no significant trend in the standing stock of either species with time although there was a significant seasonal effect higher values in February as compared to August. Information from bottom trawls during the surveys supports these conclusions. The results have been considered in the context of a food web from which it is concluded that in order for sufficient food to be present for the Nile perch there must be a significant proportion of the decapod crustacean Caridina present. It is noted that this species can be estimated acoustically using multifrequency echosounders but is very difficult with the single frequency system used on the 1999-2002 surveys. Refinements in the methodology will permit the simultaneous assessment of several key components in the food web and open the way to effective ecosystem-based fisheries management. © 2012.


Grant
Agency: European Commission | Branch: FP7 | Program: CSA-CA | Phase: KBBE-2007-1-2-11 | Award Amount: 1.07M | Year: 2008

It is widely recognised that scientific efforts need to be coordinated to strengthen the knowledge base in support of policy-making in a global context. This is a complicated task that requires effective coordination and cooperation among States, RFOs and other agencies. States with an obligation to ensure sustainability of the resources they exploit should seek (i) to promote responsible fisheries and (ii) to promote good, coordinated scientific research. In the case of the EU, actions should be consistent with major international agreements (UNCLOS, CCRF, UNIA, WSSD) and contribute to improving coherence between different EU Policies. The purpose of this Coordination Action is to facilitate a coherent approach towards research directed at the assessment and management of fish resources. The targets are particularly those areas where the European fleet is fishing in international or third country waters, or where the EU has important development goals. Thus, the principal objectives of TXOTX are: To collate information from all RFMO/RFOs and Fisheries Partnership Agreements as well as selected additional regions of special interest (with emphasis on CPA areas) on the extent of scientific research programmes being undertaken by the various actors. To analyse the data available and methodologies applied in assessment and management procedures regionally, in order to identify data and research gaps and opportunities for greater research coordination that may be promoted by the EU in support to scientific advice to fisheries management. To develop recommendations on how to improve cooperation with third parties in order to enhance research and resource status The TXOTX consortium proposes to build a network of scientists in countries with a strategic geographical distribution to produce a synthesis of data collection standards, assessment methods, management procedures that will be disseminated among participants, stakeholders and public in general


Okuku E.O.,Kenya Marine and Fisheries Research Institute | Okuku E.O.,Catholic University of Leuven | Peter H.K.,Tanzania Fisheries Research Institute
International Journal of Environmental Research | Year: 2012

The study aimed to come up with a list of specific macroalgae species, which could be used to biomonitor specific metal elements in the coastal waters of East Africa. Water extraction, EDTA, aqua regia extraction and optimized BCR 3-step sequential extracts were used to mimic bioavailable metals under various environmental conditions. The results indicated that Ulva lactuca could be used as a biomonitor to predict BCR 3-step sequential bioavailable Al, Cd, Co, Fe, Mn, Zn and Ni whereas Sargassum species could be used as a biomonitor for BCR 3-step sequential bioavailable Co, Cu, Fe, Mn and Zn. In Sargassum spp. only Co showed significant correlation with concentration in sediment's aqua regia extracted metals whereas in Ulva lactuca only Al, Co, Cu and Fe showed significant correlation with total metals extracted through aqua regia procedure. This study therefore recommends the use of Ulva lactuca and Sargassum for biomonitoring of Al, Cd, Co, Fe, Mn, Zn, Ni and Co, Cu, Fe, Mn, Zn respectively. The study recommends the use of labile fraction of BCR sequential extraction for screening of macroalgae to be used for heavy metal pollution monitoring in East Africa region.


Kimirei I.A.,Radboud University Nijmegen | Kimirei I.A.,Tanzania Fisheries Research Institute | Nagelkerken I.,Radboud University Nijmegen | Griffioen B.,Radboud University Nijmegen | And 2 more authors.
Estuarine, Coastal and Shelf Science | Year: 2011

Tropical shallow-water habitats such as mangroves and seagrass beds are widely acknowledged as important juvenile habitats for various coral reef fish species, most of which are commercially important to fisheries. Spatio-temporal variability in ontogenetic habitat use by fish among these tropical coastal ecosystems has rarely been investigated, yet there are sufficient reasons to believe that this plays an important role. In the present study, we test the spatio-temporal variability in patterns of ontogenetic habitat use by some mangrove/seagrass-associated coral reef fishes (Lethrinus harak, Lethrinus lentjan, Lutjanus fulviflamma and Siganus sutor). Abundances of these four species were investigated during two years in Tanzanian coastal waters, using underwater visual census in mangrove, seagrass, shallow and deep mudflat, and shallow and deep coral reef habitats. The study covered four distinct seasons of the year and was done at two spatially separated (>40. km) locations. Averaged across locations, seasons and years, juveniles (≤10. cm length) of the four study species had significantly higher relative densities in shallow-water (mangroves and seagrass beds) than in deep-water habitats (deep mudflats or coral reefs), whereas the opposite pattern was found for the adults (>15. cm). These findings suggest a strong and general pattern of ontogenetic habitat shifts from shallow- to deep-water habitats. However, specific habitat-use patterns of juveniles as well as adults differed significantly in time and space. Various species showed subtle to considerable flexibility in juvenile as well as adult habitat use across seasons, years, or at different locations. Furthermore, for some species the data suggest presence of ontogenetic habitat shifts at one location but lack thereof at the other location. In summary, ontogenetic habitat use needs to be considered at various spatial and temporal scales for the interpretation of habitat utilization by fish during different life stages. This is important for conservation and management of these habitats, as essential habitats or seasons may be ignored or over-emphasized with respect to their importance for fish during different parts of their life cycle. © 2010 Elsevier Ltd.


Ngupula G.W.,Tanzania Fisheries Research Institute | Mlaponi E.,Tanzania Fisheries Research Institute
Aquatic Ecosystem Health and Management | Year: 2010

The abundance of Nile shrimp, Caridina nilotica (Roux) in Lake Victoria has fluctuated significantly over time, from the periods of 1900-1950s, 1980s-1990s and from 2000s to present day. To elucidate its current abundance, its contribution to the Rastrineobola argentea fishery catches, and its importance to the composition of the diet of Nile perch (Lates niloticus L.), and to the bottom trawl catches, were investigated. From August 2006 to January 2007, the mean C. nilotica CPUE was 1.68 ± 1.20 kg boat-1 day-1 at Kijiweni and Igombe, and its 0.37% contribution to the R. argentea total catches was insignificant. Of the 230 Nile perch stomachs containing prey items, C. nilotica comprised 54% by volume of the diet of fish <50 cm TL; while haplochromines contributed 41% to the diet of fish >50 cm TL. Mean catch rates of C. nilotica in bottom trawls in 8 months between 2005 and 2008 ranged between 0 and 2.45 ± 2.50 kg hr-1. Low catches of the C. nilotica in the R. argentea fishery, and the dietary shift of Nile perch of >50 cm TL to once again include haplochromines, may indicate a decrease in C. nilotica's abundance in the lake, and vice versa. Overfishing and the selectivity of the fishery to take only large Nile perch for fish filleting factories, have resulted in reduced stocks and dominance of juveniles in the perch's populations. The highly reduced Nile perch stocks are currently leading to an apparent reversal of the 1980s regime with a shift to a new cichlid-dominated and C. nilotica low abundance state. Increase in predation on juvenile C. nilotica by the recovering haplochromines, and juvenile perches, as well as environmental degradation, especially eutrophication and pollution, along with the effects of global warming impacts, account for the observed decline in C. nilotica. © 2010 AEHMS.


Ngupula G.W.,Tanzania Fisheries Research Institute | Kayanda R.,Tanzania Fisheries Research Institute
African Journal of Aquatic Science | Year: 2010

Benthic macroinvertebrate community composition was investigated in 2008 at 55 stations at various depths in the nearshore and offshore waters of Lake Victoria, in relation to dissolved oxygen, pH, temperature, chlorophyll a and conductivity. Macroinvertebrate abundance was higher in the shallow nearshore waters than in the deep offshore waters. The communities of the shallow, intermediate and deep environments were composed mainly of molluscs, worms and insects. Gastropods (52.68%) and bivalves (40.18%) constituted the major part of the benthic community. Bellamya unicolor, Melanoides tuberculata and Coelatura spp. were the most abundant molluscs. Various macroinvertebrates showed depth preferences, with gastropods having a strong preference for shallow waters and bivalves a weak preference for deep waters. The present findings contrast with those of most studies done before 1984, but agree with many done after that period. The presence of macrophytes and abundant detritus, a food resource for macroinvertebrates, account for their high abundance in shallow waters. © NISC (Pty) Ltd.

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