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- Krause, Gesche, et al.
(författare)
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Prospects of Low Trophic Marine Aquaculture Contributing to Food Security in a Net Zero-Carbon World
- 2022
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Ingår i: Frontiers in Sustainable Food Systems. - : Frontiers Media SA. - 2571-581X. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- To limit compromising the integrity of the planet, a shift is needed towards food production with low environmental impacts and low carbon footprint. How to put such transformative change towards sustainable food production whilst ensuring food security into practice remains a challenge and will require transdisciplinary approaches. Combining expertise from natural- and social sciences as well as industry perspectives, an alternative vision for the future in the marine realm is proposed. This vision includes moving towards aquaculture mainly of low trophic marine (LTM) species. Such shift may enable a blue transformation that can support a sustainable blue economy. It includes a whole new perspective and proactive development of policy-making which considers, among others, the context-specific nature of allocation of marine space and societal acceptance of new developments, over and above the decarbonization of food production, vis a vis reducing regulatory barriers for the industry for LTM whilst acknowledging the complexities of upscaling and outscaling. This needs to be supported by transdisciplinary research co-produced with consumers and wider public, as a blue transformation towards accelerating LTM aquaculture opportunities in a net zero-carbon world can only occur by considering the demands of society.
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| 2. |
- Mirera, David Oersted, 1975-
(författare)
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Capture-based mud crab (Scylla serrata) aquaculture and artisanal fishery in East Africa- Practical and ecological perspectives : Mud crab ecology and aquaculture
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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