Lakes, rivers and oceans provide unique resources and support fisheries and aquaculture worldwide. The fisheries and aquaculture sector of Kenya contributes approximately 0.8% to the country’s GDP. Marine production is about 9 000 tonnes per year. Marine finfish form the bulk of the marine production, while shellfish (e.g. prawns, lobsters and crabs), molluscs (e.g. octopi and squids) are underexploited. The Fishery sector has the potential of about USD 5 billion for the Blue Economy in Kenya. Crab fishery in Kenya is active in some areas of the south and north coast. The crab resources along the Kenyan waters are diverse and a variety of species are edible. The most commonly fished crab by artisanal fishers is the Mangrove Mud Crab Scylla serrata. Semi-commercial and industrial fishers usually have portunid and other deep sea crabs as by-catch in trawl and longline fisheries, which in many cases are unutilized. Exports of live crabs have increased over the years, with exports mainly to Asian countries. Export of frozen crabs started recently. The need to sustainably utilize lake, river and ocean resources is recognized and important in promoting Blue Economy. Sustainable development of crab fishery provides a potential area for the Blue Economy development in Kenya. Research is essential to crab fishery development.
All waterbodies, including lakes, rivers, and underground water, in addition to seas and the coast, are unique resources. Lakes, rivers and extensive oceans form the base of Blue Economy. The biotic resources of these water bodies allow for expansion in fishing, aquaculture, mariculture sectors and foster the emergency of vibrant pharmaceutical, chemical and cosmetics industries in many developing nations (ECA, 2016). The extraction of mineral resources and the generation of new energy resources provide the feedstock to resource-based industrialization.
Oceans and freshwater sources provide livelihood and employment to millions of people. The Great Lakes, for example, offer the world’s most abundant surface fresh water reserve, holding 20% of world’s fresh water (Campbell et al, 2015). The growing water resource scarcity globally is creating pressure on water‐intensive human activities, making the potential for utilization of Lakes important for economic benefit and Blue Growth (Mayer et al., 2016).
It is estimated that fish provide more than 4.2 billion people with more than 15 percent of their animal protein intake (FAO, 2014). Kenya’s fisheries and aquaculture sector contributes approximately 0.8 % to the country’s GDP (FAO, 2015). With an EEZ of 142 400 km2, Kenya’s marine capture fisheries produce about 9 000 tonnes per year valued at USD 12 million. Marine finfish are highly exploited and form the bulk of the marine production, while shellfish (e.g. prawns, lobsters and crabs), molluscs (e.g. octopi and squid) are underexploited. The Fishery sector has much more potential (estimated to be about USD 5 billion) for the Blue Economy in Kenya; it is also crucial in contributing towards achieving the Sustainable Development Goals such as providing food and ending poverty.
Seafood plays a key role in fighting hunger and malnutrition worldwide. It provides a good source of proteins, healthy fats and essential nutrients. Over 10 million people in Kenya currently suffer from chronic food insecurity and poor nutrition. In Kenya, consumption rate of fish is 4.1 kg of fish per year, excessively low compared to the global average rate of 20 kg (Obiero et al., 2019). In addition, the demand for fish and fish products is increasing, yet many marine fisheries resources such as crabs remain unexploited. Exploitation of such resources can reduce the pressure on fish and promote sustainable utilization of fishery resources.
Despite the ecological and economic importance of crabs, few studies on crab fishery and sustainability have been performed in East Africa. In Kenya, the crab fishery is focused mainly on one species, the Mangrove Mud Crab Scylla serrata and to a lesser extent the Blue Swimming Crab Portunus pelagicus. There is lack of information on other edible species of crabs that can be fished. The aim of this study was to review the status of crab fishery in Kenya and identify unexploited crab resources. This information is important for sustainable development of fisheries and promoting Blue Economy in Kenya.
A review of crab fishery in Kenya was done by searching literature from publications and reports on crabs from the Kenya Marine and Fisheries Research Institute Library and the internet. The study covered the Kenya coast with major crab fishery areas in Lamu, Mida creek, Kilifi in the North coast and Vanga, Majoreni and Gazi in the South coast. An analysis of potential underutilized crab resources of Kenya was done from survey and reports from commercial fishers of Kenya. The species of crabs with potential for crab fishery and promotion of Blue Economy were listed and described.
Results and Discussion
Crab fishery in Kenya
Crab fishery in Kenya is active in some areas of the south coast (e.g. Vanga, Majoreni and Gazi) and north coast (e.g. Lamu, Mida Creek and Mtwapa) (Mirera, 2017). The crab resources along the Kenyan waters are diverse, and a variety of species are edible including those of the families Lithodidae, Macidae, Caneridae, Portunidae, Xanthidae, Potamidae and others (Muthiga, 1986). However, very few of these species form important food source for the local communities. Mangrove Mud Crab Scylla serrata is the most commonly caught by artisanal fishers (Fondo et al., 2010; Onyango, 2002). Commercial fishers usually have portunid and other deep sea crabs as by-catch; which in many cases are unutilized.
Globally, the demand for seafood is increasing as human population increases. The high quality and value of Mud Crab meat makes it an important source of income and its fishery is a significant economic activity in coastal Kenya. Crabmeat is popular in tourist hotels and crabs enter the export market along East Africa (Muthiga, 1986; Barnes et al., 2002). In Kenya, Mud Crab (S. serrata) has been harvested for a long time, from mangrove holes during daytime low spring tides by expert fishers (Fondo et al., 2010; Mirera, 2011). Mud Crab fisheries in Kenya are traditional in nature, using simple fishing gear such as poles, sticks and poles (Fondo et al., 2010). The fishery is dominated by men (90.3 %) aged between 23 and 55 years (Fulanda et al., 2009). A number of Fishing communities are involved in Mud Crab fisheries; however, due to the nature of the fishery, it is difficult to collect representative data to provide information on the trends of catch rates of the fishery.
The sizes of crabs and type of market determine prices. Crabs of less than 500 g are sold at US $8 kg-1 and those more than 1 000 g at US $15 kg-1. Crab for local consumption are sold from USD 0.2-0.5 kg-1 ; those sold to private homes and tourist hotels go for USD 2-5 kg-1 and US $8-15 kg-1 for export markets (Mirera et al., 2013). However, the revenue accrued from the fishery is poorly represented in national production statistics, because the market is not well defined and poorly monitored. Fishing for sub-adult and juvenile crabs is mainly done by women and children who collect them in order to meet subsistence needs. Recent surveys show that the individual weight of crabs caught currently range between 0.25-0.9 kg, which is a marked decline from 0.5-1.5 kg recorded 2-3 decades ago (Fondo et al., 2010; Muthiga, 1986; Onyango, 2002). A study on the crab size frequency showed normal distribution with female crabs being markedly smaller than male crabs (Fondo et al., 2010).
In the 1980s, crab production was approximately 20 tonnes in Kenya (Mutagyera, 1981). Mud Crab fisheries production has generally increased from 90Mt in 1990 to more than 250Mt in 2013 (Figure 1), with a corresponding increase in value and diversified market outlets. The main rich areas along the Kenyan coast include Vanga, Shimoni, Majoreni, Ngomeni, Gongoni and Karawa. Small landings also occur at Malindi, Kilifi and Lamu (Fisheries Bulletin, 2013). Lamu County is ranked the highest producer of Mud Crabs at 49.7% followed by Kwale 26.9%, Mombasa 11.2%, Kilifi 11.9% and Tana River 0.3%. The Mud Crab catch per unit effort has been estimated at 0.25-1.7 kg hr-1 and with a fisher spending between 2.5-5.0 hours fishing in a day (Mirera et al., 2013).
In recent years, increased interest has been demonstrated in Mud Crab farming in Kenya. However, hatcheries providing seed for the industry are lacking (Mwaluma, 2002; Mirera, 2011). In most of the crab farming ventures, crabs are collected from the wild for fattening (Mirera and Mtile, 2009). Studies have shown that juvenile crabs are collected in intertidal zones that are accessible to a wide range of crab collectors who cannot enter the mangrove forests to get bigger crabs (Mirera et al., 2013). The increasing demand for crabmeat creates a need to develop the aquaculture, targeting all stages. Crab aquaculture has a great potential in boosting the Blue Economy in Kenya. However, for sustainable Blue Growth, policies and regulations on crab fishery and culture need to be developed.
Mud Crab in Kenya are exported mostly as live crabs to several destinations including: China, Hong Kong, South Korea, Lebanon, Nigeria, Qatar, Singapore, Sri Lanka, Taiwan, Tanzania, Thailand, United Arab Emirates (UAE) and Vietnam. The most common destinations are Singapore, UAE, China and Thailand. Markets for frozen crabs include Belgium, China, Italy, South Korea, Netherlands, South Africa and Spain.
Several companies (establishments) have engaged in Mud Crab exportation. Between 2005 and present, about 39 establishments exported live mud crabs at some point; with Freshery Incorporation, Indian Ocean Marine Aquarium and Zero Degree Seafood exporting most of the crabs. Currently, there are about 14 establishments exporting live crabs, with Tsavo Aquarium (23.5 tonnes) and Blue Union Company Limited (15 tonnes) dominating in exports. One establishment, Zero Degree Seafood, exports live deep sea crabs.
Figure 2 shows the live exports from Kenya in quantity and value from 2004 to 2019. Mud Crab exports showed peaks in 2007 (48.21 tonnes), 2010 (43.83 tonnes) and in 2018- 2019 (approximately 60 tonnes). Exports declined between 2011 and 2016, with quantities ranging between 17 and 23 tonnes. Presently crab exports have reached approximately 58 tonnes. The value of exported live crabs followed a similar trend as that of the exported quantities, with peaks in 2007 (USD 72 000), 2010 (USD 103 000) and 2019 (upto October USD 246 000).
Exports of the live deep sea crab Pink Geryon started recently in 2018, with about 1.2 tonnes exported valued at USD 4 840. Until October 2019, about 3.7 tonnes of live Pink Geryon were exported with a value of USD 148 000. Markets for frozen crabs are mainly Spain, South Africa and Italy, ranging from 12 to 50 tonnes.
Unutilized crab resources in Kenya
Deep sea crab
Deep sea crab resources in Kenya are unutilized. Emerging crab fishery in the northern coast of Kenya, (Fig. 3) is the long line trap fishery, targeting the deep water crab, Pink Geryon (Chaceon macphersoni). A deep water crab that feeds on macrofauna, and occurrs at depths of 200 to 1025 m (Groeneveld et al., 2013). They have high variations in abundance and size over depth, substratum type and season within space and time (Groeneveld et al., 2013). In Kenya, Chaceon macphersoni) contributes 19% (by weight) of deep sea catches third after fish and prawns (Everett et al., 2015). It is a species of commercial importance in the South Western Indian Ocean region. The size ranges from 3.5 to 19.4 cm carapace length. These crabs are for export and the price is USD 1.5/ kg. Commercial fishing for Chaceon macphersoni has started in Kenya, using long line beehive fishing traps. Live deep sea crabs are exported to Asian countries particularly China and South Korea. This is a potential area for investment and can boost the Blue Economy of Kenya. There are currently four (4) licensed commercial fishing vessels targeting live deep sea crabs primarily for export.
Shallow water crabs
Some shallow water edible crabs found in Kenya include the Blue Swimming Crab Portunus pelagicus, Crenate Swimming Crab Thalamita crenata, Yellow Moon Crab Ashtoret lunaris, Spanner Crab Ranina ranina and many others. Portunus pelagicus occur in the subtidal area to a depth of 40 m, on sandy to sandy-muddy substrates in areas near reefs, mangroves, and sea grass and algal beds (Carpenter et al., 1997). It is mostly caught as by-catch in commercial prawn trawlers and artisanal fishers using nets, but is hardly fished in Kenya. The market size ranges from 14 to 20 cm (CL), with price ranges of USD 8 to 15 kg-1. Thalamita crenata inhabits shallow non-reef habitat with soft substrates, prefers areas near mangroves, on mangrove swamps or with muddy-rocky substrates in intertidal platforms (Carpenter and Niem, 1998). The market size is about 8 cm (CL). Ashtoret lunaris is nocturnal and occurs from intertidal zone to a depth of 50 m, on muddy sand or broken shells bottoms (Saher et al., 2017; Carpenter and Niem, 1998). They feed on small shellfish, worms and other small crabs at night (Saher et al., 2017). They are commercially important and are a food source in many tropical and subtropical countries. The sizes range from 4.2 to 4.5 cm (CW) and weight between 11.6 and 14.8 g; with males being larger than females (Saher et al., 2017). Ranina ranina is found at depths more than 100 m in open sandy areas in which they bury (Carpenter and Niem, 1998). The market size is about 15 cm (CL) with a weight of up to 900 g.
Crab fishing in the Kenyan coast has been practiced for decades. Local communities are dependent on crab fishery of food and income. The most commonly fished crabs are the Mangrove Mud Crab and the Blue Swimming Crab and production has increased over the years. Other edible crab resources are unexploited. Sustainable development of crab fishery provides a potential area for the Blue Economy development. However, little is known about these rich resources of Kenya. Research into the abundance, biology, ecology and distribution of crab species is essential to crab fishery development. This is particularly in reference to the emerging deep sea crab fishery, which has elicited a lot of interest by commercial fishing investors, though its biological information is limited.
We wish to acknowledge the Kenya Marine and Fisheries Research Institute and all organizers of the GLOW 9 Conference, where this work was presented.
Funding for this study came from the Kenya Marine and Fisheries Research Institute.