The last ones left: Mozambique's mysterious Dugongs
The question plagues me as a conservationist, again: are we too late to protect the last ones? Are Bazaruto’s dugongs soon to become a myth?
This population off Africa’s east coast is estimated at no more than 250 animals. They could all vanish in as little as 40 years according to the Convention on Migratory Species of Wild Animals (October 2010).
Unless Mozambique’s last viable Dugong population is afforded adequate protection through effective law enforcement, they have no chance of urvival.
Dugong are long-lived, slow breeding, marine herbivores, and one of the most endangered of marine mammals. Should they become accustomed to people, these animals are completely approachable, and in the most fortunate of circumstances may even be stroked by the extremely privileged diver.
Dugongs become sexually mature between 10 to 17 years, and are able to produce a single calf after a gestation of 13 to 15 months. The calf can suckle for up to 1.5 years, and the interval between calving is estimated at 3 to 6 years. Male Dugongs are able to attain a length of 3.5m and weigh up to 400kgs. The International Union for Conservation of Nature (IUCN) lists the Dugong as Vulnerable at a global scale and reports an estimated population decline of 20% in the last century.
Today, the Dugong is represented in 48 countries throughout its former range by relic populations. They are found from the coast of East Africa to Vanuatu in Oceania, along the Indo-Pacific. The global Dugong stronghold occurs in Australia where their numbers have been estimated at 50,000 individuals. The second largest population is found in the Arabian Gulf, followed by the Red Sea population, estimated at 7,000 and 4,000 animals respectively.
The Dugong’s African range formally included the coasts of Eritrea, Somalia, Kenya, Tanzania, and Mozambique, also including Madagascar and the islands of Reunion, Mayotte, the Comores and the Seychelles. Based on a rapid national assessment conducted in 2004, their numbers here have been reduced to no more than a handful. The assessment concluded that Mozambique’s Bazaruto Archipelago is host to the last viable group of Dugongs along East Africa’s coast.
Dugong distribution aligns with the presence of seagrass, their food source. These flowering marine plants are found in protected and sheltered bays and archipelagos up to depths of 58 m, but are more common in Mozambique at 5 to 15 m. Not only do seagrass meadows provide Dugongs with food, but they also rank as one of the world’s most productive ecosystems.
Dugongs are able to consume up to a tenth of their body mass in seagrass per day, and are known to select for certain species with high nitrogen content and lower fiber. If a Dugong is unable to consume the preferred quantity and quality of forage, this can delay breeding and limit lactation. To date, the Indian Ocean has lost 60% of its seagrasses as a result of human induced disturbances. These include dredging, coastal pollution, and sedimentation from over-silted river loads.
When fertilizer is deposited into the ocean via rivers that pass through agricultural lands, the result is an algal bloom on the surface of sea- grass leaves. The algae block sunlight and so inhibit the process of photosynthesis. Large scale seagrass losses have occurred as a result of these algal blooms.
The IUCN recently placed importance on seagrasses as a significant carbon sink. The grasses are able to sequester large amounts of carbon in their below-ground tissue (roots and rhizomes), and are known to store up to 15% of atmospheric carbon. Losing one hectare of seagrass is therefore almost the same as losing one hectare of tropical forest.
Up to 80% of Mozambique’s coastal human population relies on marine resources for their primary livelihood. Their main forms of harvesting are through seine and gill netting. The seine net consists of a long curtain of nylon net- ting and a hauling rope attached to each end. Fishermen normally anchor one end of the net on an exposed sandbank, and use boats to drag the opposite end of the net into and “arc”. Once both ends of the net meet, they are hauled inward. The net is dragged along the ocean floor in this process, and seagrasses are uprooted, or their leaves are torn from the rest of the plant.
The secondary effects of seining are also detrimental to seagrasses. Continuous fishing in the Bazaruto Archipelago appears to have reduced predatory fish stocks, creating an opportunity for sea urchin populations to proliferate. Urchins can consume seagrasses to a point where meadows are overgrazed and cannot recover. In spite of habitat loss, gill netting has been identified as the most significant threat to Dugongs.
When they attempt to surface for air, Dugongs regularly become entangled in unattended nets. Many marine mammals are at risk of extinction from the con- sequences offisheries bycatch. This threat appears to have increased in frequency and intensity over time as a result of human population escalation and the commercialisation of fisheries.
A marine species bycatch workshop in 2006, convened through the Western Indian Ocean Marine Science Association (WIOMSA), concluded that coastal gill net fishery poses a serious threat to Dugongs, particularly in the western reached of the Indian Ocean. The bycatch workshop acknowledged that while turtles, Dugongs, sharks and cetaceans such as the whales, dolphins and porpoises are all impacted by fishery activities, the highest priority is the Dugong, which remains severely threatened by gill netting.
There are limited measures to mitigate bycatch in the Western Indian Ocean, and currently none are enforced in Mozambique. However faint, a glimmer of hope exists. The Endangered Wildlife Trust (EWT) is in the process of lending support to the protection of this charismatic species, and is in discussion with the National Government of Mozambique.
If the EWT, its partners including the WWF and the range of government departments and institutions involved in Dugong conservation can consolidate their efforts towards effective law enforcement, Dugongs have a chance. The time to act is now, we can no longer ignore the Dugong’s precarious hold on survival.
Karen Allen is the project executant for the Endangered Wildlife Trust’s Dugong Emergency Protection Project (email@example.com.)
This article originally appeared in the Mail & Guardian newspaper as an advertorial supplement