Saturday, 10 June 2017 12:47

Dugongs: The gem of the Western Indian Ocean

By Kenneth Esau Oduol

[Kisite Mpunguti Bay, Kenya] In the past Dugong were widely distributed along the southern coast of Kenya. However, over the years a decline in the index of species abundance and extent of occurrence has been reported. Kenyan Marine expert suspect that without targeted species conservation efforts in the immediate and longer term these numbers will reduce further. Sightings of the Dugong have also reduced when compared to the last ten years.

 

The mighty Dugong, a gem of the Indian Ocean [Image: CC-GBR]

The importance of the conservation challenges facing this species is increasingly recognized in Kenyan and global conservation circles. However, few solutions have been developed, and management policies are poor, weak or lacking in the vast majority of the affected regions, Kenya included. Conservationists have recognized this urgent need to resolve these problems. In response, efforts at enhancing research and advice, among other issues, on the development and implementation of a suite of national and local area conservation and management strategies for Dugong conservation have been initiated. The enhanced education and awareness campaign on Dugong conservation will contribute to these efforts to conserve these species in the short and long term.

Background

Dugongs form a vital component of Kenya’s natural ecosystem and play a critical role in Kenya’s conservation and tourism industry.  In recognition of this, marine experts, conservationists and stakeholders in Kenya have directed their efforts in a bid to conserve the remaining Dugong populations. Some of the efforts currently being implemented include; enhanced research about species in Kenya, increased surveillance and protection, education, awareness and sensitization of the coastal communities on the status of the species including threats to their survival among others.

Nguva as it is known in Swahili is currently under threat. It has played a role in legends and traditional stories in Kenya where the coastal communities of the Miji Kenda have known the animal as the "Queen of the Sea". 

Biology& Conservation Needs of the Dugong

The Dugong is a herbivorous medium sized marine mammal that resembles the Manatees in bodily characteristics. It belongs to the order Sirenia and can be found in areas that largely support the growth of sea grass. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative,  Steller's sea cow (Hydrodamalis gigas). The IUCN lists this species of marine creature as a vulnerable species-high risk and endangered in the wild. 

 The Dugong is a herbivore with seagrass as its main staple [CC-GBR]

The dugong has a fusiform body with no dorsal fin or hind limbs. The forelimbs or flippers are paddle-like. The dugong is easily distinguished from the manatees by its fluked, dolphin-like tail, but also possesses a unique skull and teeth. Its snout is sharply downturned, an adaptation for feeding in benthic sea-grass communities. The molar teeth are simple and peg-like unlike the more elaborate molar dentition of manatees.

Dugongs have few natural predators and are social animals. When sighted in the wild they are usually two due to the carry capacity of the habitats.

Current Distribution and Geographical Range

The Dugong has a large range that spans at least 37 countries and territories and includes tropical and subtropical coastal and island waters from east Africa to Vanuatu, between about 26° and 27° north and south of the equator.

The dugong is largely dependent on seagrass communities for subsistence and is thus restricted to the coastal habitats which support seagrass meadows, with the largest dugong concentrations typically occurring in wide, shallow, protected areas such as; bays, mangrove channels, the waters of large inshore islands and inter-reefal waters.

Dugongs are typically benthic marine species and exist in tropical waters of East Africa. The species has also been occasional sighted in deeper water where the continental shelf is broad neritic and sheltered. Since their primary source of nourishment is the sea grass, they have a broad but fragmented habitat that supports the growth of sea grass. Dugongs have previously been spotted off the coast of Kenya in Kiunga Marine Park (270 square kilometres in size) Msambweni and off Kisite Mpunguti Marine National Park. In the past they were known to occur off Somalia, Kenya, Tanzania, Mozambique, Comoros, Madagascar, and Mauritius. Current scientific research indicates that there appears to be very few individuals remaining along the coasts of Somalia, Kenya, Tanzania, Mayotte in the Comoros Archipelago, Madagascar and in Aldabra Atoll in the Seychelles Archipelago. Different habitats are utilized variedly for a myriad of activities by the Dugong’s. Tidal sand banks and estuaries are used for calving and other specialized habitats are used for mating seasons. 

Distribution and abundance of Dugong population in Kenya. Inset top Left: Lamu Archipelago

Status

The last major worldwide study, made in 2002, concluded that the dugong was declining and possibly extinct in a third of its range, with unknown status in another half. This was based on anecdotal and research data that indicates the species has been extirpated from at least 30% of their historical range in Eastern Africa- Dutton 1998. As often is the case in conservation, there is limited time series data on population status and trend of the Dugong.

Further, the IUCN currently classifies the species as vulnerable to extinction. This is largely as a result to anthropogenic factors that have continued to affect the quality of their habitat. Data indicates that the recruitment rate has been less that the requisite 5% p.a. as about 95% of the adult population does not survive the illegal human activities apart from the reduction of traditional grazing areas. This decline has been reported in the area of; abundance, occupancy, the extent of occurrence and/or quality of their habitat. In recent years Dugong numbers around the coast of Kenya in terms of abundance have greatly reduced despite Kenya having large areas of marine parks and reserves. The general impression that emerges from aerial surveys conducted in Kenya in 1973, 1975, 1980, 1994 and 1996, is that the dugong population is declining rapidly. In 1967, one herd of approximately 500 individuals was reported off Kenya's south coast. Pre-1961, ‘large’ isolated populations of dugongs were sighted at both Mombasa Marine Park and Natural Reserve and Malindi Marine National Park; however low numbers have been recorded after this date. In 1994, a maximum of 16 dugongs was sighted during aerial surveys, all within Ungwana and Malindi Bays.

Based on the aerial survey data and anecdotal information, it is estimated that Kenyan waters now contain a population of approximately 50 dugongs. In 1996, six dugongs were sighted: a herd of four individuals including one calf in the Siyu channel, and two lone animals near Manda Toto Island. However, no dugongs were seen in the most recent aerial surveys in this area. Anecdotal information suggests that a group of dugongs may migrate between Somalia and Lamu. The most recent population of the species in Kenya was reported at being between 180 and 250.

Threats to Dugongs

Dugongs along the Kenyan coast continue to be threatened by a myriad of human activities including; direct human exploitation, habitat loss and destruction, and incidental capture during fishing operations. The rate of population change is most sensitive to changes in adult survivorship. Experts view that even a slight reduction in adult survivorship as a result of habitat loss, disease, hunting or incidental drowning in nets, can cause a chronic decline in a dugong population.

The Kenya coast is characterized by high population growth rates, high reliance on natural resource exploitation for livelihood support and unplanned socio-economic activities. Thus environmental conservation has not been undertaken effectively or in some cases and locations is not ranked highly as people are pre-occupied with livelihood issues. Some of the most significant and studied threats to the species in Kenya include;

Habitat loss and degradation:  The Kenyan coast, is experiencing massive population increases and demographic changes which are resulting in environmental degradation. This degradation results from poor farming practices such as overgrazing on coastal dunes; the clearing of coastal and inland forests including the clearing of wetland vegetation (for salt pan and shrimp farm construction), and mangrove stands (for firewood and building material); and sand-mining. The result has been a massive increase in soil erosion and inshore silt loads. These activities cause increases in sedimentation and turbidity in the inshore waters resulting in degradation through smothering, lack of light and increased epiphytic growth caused by nutrient enrichment in the sea grass beds. In addition, herbicide runoff from agricultural lands also presents a potential risk to sea-grass beds functioning along the coast especially in areas adjacent to sugarcane production such as Msambweni in Kwale. 

Further, human induced processes are degrading estuarine and coastal habitats through habitat loss and sea-grass dieback affecting critical inshore dugong feeding areas. Poor land use practices are causing increased sedimentation in Malindi and Watamu areas. The increases in the silt load through erosion have affected the nutrient quality of available sea-grass while in some cases the sea-grass beds are also being destroyed by trawl nets.

Further, intensive exploitation of the marine biological resources in Kenya’s inshore waters is apparently causing changes to food web structures as indicated by an abundance of the sea urchin Diadema in areas such as Diani, on the southern beaches of Mombasa. Runoff also has bio-accumulative impacts on dugongs and other marine organisms. The above changes are decreasing the suitability of these areas as Dugong habitats and are thus believed to be altering distribution and abundance along the Kenyan coast. 

Fishing Pressure and Hunting: Evidence exists indicating that fishing pressure has major influence on marine mammal abundance and distribution. The Dugong is subject to indirect fishing mortality throughout most of its range. The fishery industry in Kenya is mostly subsistence and artisanal in nature. Artisanal fisheries mostly operate in inshore waters along the coast where it involves the use of seine or drift and bottom set gill nets from small traditional boats. Further, fishing pressure is particularly high in times of drought, when agriculture is abandoned in favour of food collection from the inshore zone. 

Dugong hunting sites marked in red [CC-STD]

The density of gill nets along the coast, particularly along the central coast is high. It is the same areas that Dugongs use as feeding grounds. To note, during these fishing operations, nets of over 100m in length are stretched across sea-grass beds in the evening. The indiscriminate spread of these nets impacts negatively on the large marine mammals such as the Dugong by entangling and ultimately drowning them. There have been reports, particularly from the Lamu Archipelago, Kenya that dugongs commonly drown in set nets along this coast. Additionally, the fishing operations also enhance the risk to the animals as they can be ambushed by boats as they move onto or off the shallow sea-grass beds. Illegal fishing activities such as use of dynamite by fishermen to exploit resources associated with the fringing coral reef also kill Dugongs contributing to further loss of the species.

According to surveys, including interviews with fishers on by-catch on most Beach Management Units- BMU along the coast there are revelations that Dugongs are taken in the drift gill net fishery. However, there are no records of the numbers of dugongs taken through these by-catches. 

Hunting is also considered to be one of the factors causing the decline in Dugong numbers along the south coast of Kenya. Traditional hunting of dugongs in Kenya involved the use of harpoons. Kenyan coastal communities traditionally use different parts of the dugong for food, medicinal and ornamental purposes. Dugong oil is also used as fuel for lamps, and together with powdered bones and the inhalation of smoke from burning bones, is believed to cure a variety of ailments from tooth aches to labour pains. Pieces of tusk and bone are also worn by children as charms to ward off evil spirits. 

Additionally, Dugong meat is very popular among the coastal inhabitants in Kenya. Communities such as the Bajuni tribe who live between Lamu and the Somali border, preferred it to veal or pork as they are predominantly Muslims. Currently, legislation bans the hunting of dugongs.

Vessel strikes and traffic; The near shore areas where dugongs occur have become an easy and convenient source of food and income. Fishing activities often makes Dugongs vulnerable to ambush by boats as they move onto or off the shallow sea-grass beds. Increased vessel traffic in the Dugong’s range increases the likelihood of strikes apart from scarring of sea grass beds by boats propellers in shallow waters. Additionally, the tourism activities such as diving and snorkeling bring boats close to these areas further threatening their populations from boat accidents and acoustic disturbances and impacts due to boat traffic. Presumably, high levels of vessel traffic in such areas could prevent Dugongs from using available intertidal sea-grass meadows. 

Some of acoustic effects might include;  interference with the animal’s natural acoustic communication signals ; damage to their hearing systems, and behavioural changes including disturbance reactions, ranging from brief alterations in behaviour to short- or long-term effects on individuals or populations.

Tourism: The expansion of ecotourism has resulted in the establishment of tourism operations associated with Dugong-watching cruises at several locations along the coast. This activity contributes to Dugong mortality especially with regard to disturbance and at times illegal catch. The selling of food and items and such,  as well as fashioned ornaments and jewellery from shells, bones and tusks to tourist as rings and nose plugs also leads to capture and decline of the species.

Hotspots

To date, the approaches to sea-grass protection has largely been through marine parks and fishing industry closures to prevent structural damage to sea-grass beds through trawling. There have also been few attempts to protect sea-grass beds from adverse impacts on ecosystem processes especially those associated with land use. Some of the Dugong conservation hotspots that have been identified and there is need for increased marine parks.

Conservation Efforts

Unless human values change drastically, experts believe that it will be impossible to completely eliminate anthropogenic impacts to the Dugong populations along the Kenya coast. This then makes the objectives of maintaining dugong numbers at present and facilitating the recovery of depleted populations as a strategic action is much more realistic. This will not be achieved if the only trigger for management intervention in an area is a demonstratively declining population. Some of the management interventions that have been used to either protect or conserve the species in Kenya are;

  • Legislative through the Wildlife Conservation and Management Act and Fisheries Act; under the wildlife act Dugongs are completely protected and KWS ensures their conservation. Within the fisheries act artisanal fishing practices are defined i.e. no trawling within the 5 nautical mile range.
  • Identification of areas that still support significant numbers of dugongs especially in officially designated protected areas, community managed coastal zones and control of land use adjacent to Dugong habitats
  • Integration with extensive local involvement how impacts on dugongs can be minimised and the habitat protected in these key habitat areas.

For management interventions to be effective, some of the proposed conservation initiatives include; enhanced knowledge of the status of the species through research to estimate current distribution and relative abundance, habitat mapping and use and fishing impacts. Additionally, there is urgent need for the general public to be concerned about Dugong conservation. This can be achieved through; the development of culturally appropriate education and awareness campaigns targeting critical Dugong habitats. This sensitization can be at various levels including those that focus on children and fishermen. Education of locals about the importance of sustaining the remaining populations also needs more emphasis such as having a Dugong march and festival in Lamu and the south coast areas. Others are to provide incentives to fishers to reduce the direct and incidental capture of dugongs and active enforcement of the laws prohibiting hunting, capture and fishing in illegal species.

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