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  • 1. Eriksson, Lars-Ove
    et al.
    Alanärä, Anders
    Andersson, Staffan
    Myter och sanningar om svensk fiskodling2003In: Torskar torsken? Forskare och fiskare om fisk och fiske / [ed] Birgitta Johansson, Stockholm: Formas , 2003, p. 103-111Chapter in book (Other academic)
  • 2.
    Mirera, David Oersted
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Capture-based mud crab (Scylla serrata) aquaculture and artisanal fishery in East Africa- Practical and ecological perspectives: Mud crab ecology and aquaculture2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Mud crab Scylla serrata is a crustacean that spends most of its life cycle in the mangrove environment throughout its range. Fishery and aquaculture of this crab are significant economic activities in coastal areas in the tropics and sub-tropics because of the meat quality and nutritional value. However there is a significant shortage of information on the ecology, fishery and aquaculture of these crabs in sub-Saharan Africa. This impacts the development of a sustainable aquaculture and fishery for the benefit of coastal communities. The present study analyses various aspects of mud crab ecology, fishery, aquaculture and social economics in East Africa using multidisciplinary approaches. The results are given in seven papers based on field and laboratory studies. The study established for the first time that high intertidal mangrove back-flats constitute a key habitat for the earliest instars of S. serrata (4 -30 mm CW). It also showed that diurnal tidal migration behaviour occurs in small juveniles that migrate to sub-tidal habitats during the day, possibly due to variable predation risks. Monthly sampling of juveniles in Kenya and Tanzania indicated continuous recruitment throughout the year. The large numbers of juvenile crabs along mangrove fringes indicate that these habitats could serve as sites suitable for collection of juvenile crabs for aquaculture. However, these areas must also be managed and protected to support the recruitment to the wild crab populations. An assessment of the crab fishery indicated that artisanal crab fishers possess significant traditional knowledge mainly inherited from their parents that enabled them to exploit the resource. Such knowledge could be useful for the development of the aquaculture and in management of the fishery. Mud crab fishing was found to be a male dominated activity, and fishers on foot practiced fishing in burrows at spring low tides. Interviews indicated that the average size of marketable crabs has declined over the years and a weak management system was observed with most fishers operating without a license. Due to the knowledge required regarding the local conditions, fishers are unable to shift to new areas. Furthermore fishers and could not fish at neap tides. Such limitations provide a “natural closure” of the fishery. Also foot fishers cover fairly limited distances in their daily operations, an aspect that can be utilized to effect site-specific management for the fishery if necessary. Laboratory and field experiments indicated that cannibalistic interactions are heavily influenced both by size differences of crabs and the availability of shelter but no significant effect was found for different stocking densities. Such information is of direct importance for crab farmers in East Africa, where seed from the wild are of multiple sizes and there is a need to grade juvenile crabs and provide shelter at stocking to ensure maximum survival. Experimental studies in earthen pond and mangrove pen cultures indicated high mortality rates. Comparing growth in earthen pond and mangrove pen systems indicated that growth rates were generally high in both systems, but significantly lower in pen systems without shelter, suggesting that shelter may have a stronger effect on growth than has been previously thought. Similar to artisanal mud crab fishery, an assessment of small-scale mud crab farming by organized community groups in Kenya indicated low level of women participation. A good knowledge of the market existed among the mud crab farming groups where hotels and exporters offered the highest prices. However there is a need for national policies to be directed to support small-scale aquaculture development by ensuring training and capacity building for women, operation and management of groups, data management and provision of user rights for communities working in the mangrove environment. Market analyses showed that the common market size of crabs in East Africa ranged between 500-1000 g and are thus larger than in Southeast Asia where the average size is reported at 300 g. Prices for mud crabs were over 50 % lower in Tanzania than in other East African countries and most of the profit was earned by middlemen and exporters. Cost revenue analysis showed that it would be more profitable to farm smaller commercial crabs, and develop a market for 300 g crabs to increase the profitability of crab farming in East Africa. Also, the same analyses found that farming large crabs in individual cages, which is the dominant culture form in East Africa today, had very low profitability due to high labor costs and low growth rates. Using a step-wise function of natural growth it was shown that growth rates of S. serrata cultured in cages was 40 % of the growth rates obtained in experimental pond and pen cultures, which were similar to natural growth. Therefore the good performance of grow-out cultures of juvenile mud crabs in earthen ponds and mangrove pens showed a potential to develop into a profitable and sustainable intervention. However, more work is needed to improve survival in culture systems and address the identified limitations of crab seeds and feed to enable development of sustainable mud crab aquaculture in East Africa.

  • 3.
    Mirera, David Oersted
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. Kenya Marine & Fisheries Res Inst KMFRI, Mombasa, Kenya.
    Moksnes, Per-Olav
    Gothenburg Univ.
    Comparative performance of wild juvenile mud crab (Scylla serrata) in different culture systems in East Africa: effect of shelter, crab size and stocking density2015In: Aquaculture International, ISSN 0967-6120, E-ISSN 1573-143X, Vol. 23, no 1, p. 155-173Article in journal (Refereed)
    Abstract [en]

    Grow-out culture of mud crabs Scylla serrata in East Africa is at an earlier development phase and is dependent on wild seed crabs. We assessed three different culture systems (net cages, ponds and pens) in three treatments (shelter, size and density) to evaluate survival and growth in small-scale culture of mud crabs in Kenya. In small nursery cages, we assessed how availability of shelter, stocking density and size-class separation affected cannibalistic rates in small juveniles (20-80 mm internal carapace width) in 7-day experiments. The result indicated that shelter and size-class separation decreased cannibalism and mortality with 26 and 31 %, respectively, whereas no significant effect was found for different stocking densities. Earthen ponds and mangrove pens were used to compare growth and survival in long-term studies (2-4 months) in the presence and absence of shelter. Treatments with and without shelter yielded low overall recovery of crabs (4-26 %) indicating high mortality rates, and there was no significant effect of shelter or culture system on survival. In contrast, growth rate was high in both pens and ponds, but significantly lower in pen systems without shelter. Generally, the results indicated that cannibalism is the largest source of mortality in different culture systems (net cages, ponds and pens), and use of shelter and size grading of crabs improved survival significantly. In contrast, growth rates were high and comparable to natural growth in both pond and pen culture when shelter was provided. Using growth models to compare growth and survival in mud crabs from aquaculture studies in the literature, we show that shelter may have a stronger effect on growth than has been previously thought, whereas crab density appears to impact more on crab survival. Thus, improving survival in grow-out culture systems is a challenge that remains to be solved for small-scale mud crab culture in East Africa.

  • 4.
    Moksnes, Per-Olav
    et al.
    University of Gothenburg.
    Mirera, David Oersted
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. Kenya Marine & Fisheries Res Inst, Kenya.
    Björkvik, Emma
    University of Gothenburg.
    Hamad, Muumin Iddi
    Univ Dar Es Salaam, Tanzania.
    Mahudi, Humphrey Matalu
    Mafia Isl Marine Pk, Tanzania.
    Nyqvist, Daniel
    University of Gothenburg.
    Jiddawi, Narriman
    Univ Dar Es Salaam, Tanzania.
    Troell, Max
    Stockholm University.
    Stepwise function of natural growth for Scylla serrata in East Africa: a valuable tool for assessing growth of mud crabs in aquaculture2015In: Aquaculture Research, ISSN 1355-557X, E-ISSN 1365-2109, Vol. 46, no 12, p. 2938-2953Article in journal (Refereed)
    Abstract [en]

    Predicting growth is critical in aquaculture, but models of growth are largely missing for mud crab species. Here, we present the first model of natural growth in juvenile and adult mud crabs Scylla serrata from East Africa using a stepwise growth function based on data on intermoult periods and growth at moult from field mark-recapture, pond and laboratory studies. The results showed a sigmoid growth pattern in carapace width and suggest that S.serrata in East Africa will reach 300g and sexual maturity similar to 9.9months after settlement, and a commercial size of 500g after 12.4months. Analyses of the literature identified several issues with the common praxis to compare standard growth measures between aquaculture studies with different initial size or growing periods. Using the new growth function to estimate the proportional difference between modelled and obtained growth as an alternative method, we show that growth rates of S.serrata cultured in cage systems, which are dominant in East Africa, was <40% of the estimated natural growth and growth obtained in pond systems. The analysis also indicated that growth rates of S.serrata in Southeast Asia was over 50% higher compared with similar culture systems in East Africa, and that different species of mud crabs had large differences in growth rates. This study shows that growth in the present mud crab aquaculture systems in East Africa is below their expected potential. Further work is needed to identify the factors behind this observation.

  • 5.
    Wamukota, Andrew
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Brewer, T. D.
    Charles Darwin University, Australia ; Arafura Timor Research Facility, Australia.
    Crona, B.
    Stockholm University ; The Royal Swedish Academy of Sciences.
    Market integration and its relation to income distribution and inequality among fishers and traders: The case of two small-scale Kenyan reef fisheries2014In: Marine Policy, ISSN 0308-597X, E-ISSN 1872-9460, Vol. 48, p. 93-101Article in journal (Refereed)
    Abstract [en]

    This study, carried out in five fishing communities along the Kenyan coast, examined fisheries-derived income of fishers and traders in two different invertebrate fisheries (octopus and sea cucumber) and tested if differences in global market integration of these two products could explain differences in income inequalities among actors involved in the two fisheries. The structure of the value chains was mapped, differences in income between fishers and traders tested, and income inequalities among actors in each fishery examined. Although the octopus fishery included a greater diversity of actors and thereby provides income to a larger group of people, income inequality in this fishery was higher among fishers and traders than in the sea cucumber fishery. Thus, the often cited relationship between increasing market integration and income inequality may require a re-evaluation and a more nuanced treatment.

  • 6.
    Wamukota, Andrew
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. Wildlife Conservation Society - Coral Reef Conservation Project, Kenya ; Pwani University, Kenya.
    McClanahan, T. R.
    Wildlife Conservation Society - Marine Program, USA.
    Global Fish Trade, Prices, and Food Security in an African Coral Reef Fishery2017In: Coastal Management, ISSN 0892-0753, E-ISSN 1521-0421, Vol. 45, no 2, p. 143-160Article in journal (Refereed)
    Abstract [en]

    This study evaluated the potential impact of global fish trade on local food prices by analyzing a 16-year locally collected time series of disaggregated coral reef fish products and prices that differed in their market chain linkages-ranging from local to international markets. We were primarily interested in evaluating how local and global markets interacted with the local prices of beef, fish, and maize. There was no cointegration between the prices of exported octopus and that of maize and beef over this study period. Further, the three types of fish and associated markets responded in different ways to various price changes. For internationally traded octopus, we found a positive association between price and catch rates but no evidence that the global trade in octopus markets created local inflation, particularly the prices of the fish eaten by the poor. In general, there was no evidence for price transmission from export to nonexport fish products even though fishers appeared to focus on octopus when prices were high. Consequently, fishers' behaviors and trade policies that promote adjusting fishing effort to internationally traded fish did not appear to promote poverty or food insecurity in this fishery.

  • 7.
    Wanyonyi, Innocent Ngao
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. CORDIO EA, Kenya.
    Wamukota, Andrew
    Pwani Univ, Kenya.
    Mesaki, Simeon
    Univ Dar Es Salaam, Tanzania.
    Guissamulo, Almeida Tomas
    Univ Eduardo Mondlane, Mozambique.
    Ochiewo, Jacob
    Kenya Marine & Fisheries Res Inst, Kenya.
    Artisanal fisher migration patterns in coastal East Africa2016In: Ocean and Coastal Management, ISSN 0964-5691, E-ISSN 1873-524X, Vol. 119, p. 93-108Article in journal (Refereed)
    Abstract [en]

    Migration is a feature of most small-scale fisheries across the world and has previously been described in spatial and temporal terms. This study assessed spatial and temporal migration patterns of fishers in Kenya, Tanzania, and Mozambique from October 2009 to March 2010 covering important migrant fishers destinations on the coast The concentrations, fishing destinations, routes, frequency as well as seasonality of migrant fishers in each of the countries were assessed using 192 surveys at 9 sites and 127 semi-structured interviews at 25 sites. Migrations in Kenya and Tanzania were mainly seasonal while in Mozambique circular migrations were common and lasted far longer. Fishers from Pemba, Unguja and Nampula were the most experienced migrant fishers in terms of the numbers involved and their ability to migrate to distant destinations. The region is likely to experience increasing influxes of migrant fishers due to increasing fisher numbers, fisheries governance, and other factors that provide an environment conducive to migration. The small scales of operation of the local co-management structures, the lack of monitoring ability and the limited knowledge about activities of migrant fishers requires a shared regional approach in terms of fisheries management with specific attention to issues concerning migrant fishers. (C) 2015 Elsevier Ltd. All rights reserved.

  • 8.
    Wanyonyi, Innocent Ngao
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Wamukota, Andrew
    Pwani University, Kenya.
    Tuda, Paul
    Leibniz Centre for Tropical Marine Ecology (ZMT), Germany.
    Mwakha, Victor Alati
    Kenya Marine and Research Institute, Kenya.
    Nguti, Lydia Mukii
    CDC-Kenya Medical Research Institute, Kenya.
    Migrant fishers of Pemba: Drivers, impacts and mediating factors2016In: Marine Policy, ISSN 0308-597X, E-ISSN 1872-9460, Vol. 71, p. 242-255Article in journal (Refereed)
    Abstract [en]

    Most of the fishers of coastal East Africa particularly among the Bajuni, Kojani, Macua and Vezo ethnic communities have historically practiced migration. This study explores the strategies used by migrant fishers' of Pemba in the Western Indian Ocean region. By adopting a modified sustainable livelihoods framework (SLF), the study uses in-depth interviews and questionnaires to explore the life histories of the fishers in migrant communities, their motivations to migrate, and their associated socioeconomic and ecological implications. Results point out to a complexity of factors contributing to migration including natural, to economic and social factors. Interaction of such factors is instrumental in shaping fisher migration as an activity into an important livelihood strategy. The study concludes that SLF provides holistic understanding of migration. However the incorporation of the 'livelihood spaces' extends this knowledge by integrating the spectrum of spatial aspects. This understanding is critical in the design of policies and interventions necessary to ensure resource sustainability and secure fishers livelihoods. This multi-method approach is critical in empirical study of fisher migration.

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