The global status of dugongs in the context of their biology Helene Marsh

Conservation Significance of Dugongs Only member of family Dugongidae Class:Mammalia Order: Sirenia Family: Dugongidae Species: DugongDugong dugon Steller’s sea cowHydrodamalis gigas (extinct) Family:Trichechidae Species:Antillean manatee Trichechus manatus Amazonian manateeTrichechus inunguis West African manateeTrichechus senegalensis All extant sirenians vulnerable to extinction

Conservation Significance of Dugongs Only strictly marine herbivorousmammal Largest population size (>100,000) and range of extant sirenians

Seagrass Specialists Mouth specialised for bottom feeding Remove all parts of plant (leaves and rhizomes) Leave feeding trails and feeding plumes Like nutritious new growth – possibly farming large areas when in large herds

Life History Lifespan 70+ yrs Age first breeding 6-17 yrs Litter size 1 Calving interval  2.5 yrs Gestation period months Lactation ~ 1.5 yrs Adult survivorship > 95% Max rate of increase  5% Sustainable harvest ~ 2%

If Vietnamese waters support only a small population e.g. 100 dugongs then ANY mortality from human causes is potentially unsustainable

Movements Have tracked > 60 animals Most movements local Several animals made long-distance movements Longest movement ~800 km in few days

Movements of satellite- tracked dugongs –42 dugongs tracked on the east coast days –Covered over 80% of coast –1/3 moved linear distances >80km –1/6 moved >150km 1500km 280km 400km Shoalwater  Bay Cooktown  Townsville 

Preliminary information on genetics of female dugongs Genetic types of female dugongs from Southeast Asia (Indonesia, Thailand, Philippines) generally distinct from those from Australia Two partially overlapping maternal lineages in Australian coastal waters Pattern reflects ancient separation due to sea level change with modern incomplete mixing –Dugongs colonise new areas only rarely –Males only may be moving and breeding

Main Conclusions from Biology Rate of change in dugong numbers is very sensitive to changes in adult survivorship Impact of mortality (drowning in nets, boat strikes, hunting) on dugongs is serious When dugongs don’t have enough to eat because of habitat loss, they delay breeding or move - this reduces the level of mortality that is sustainable

Dugong conservation MUST address the issues of habitat conservation AND mortality reduction Dugong conservation in Vietnam should be developed in consultation with neighbouring countries - China, Thailand and Cambodia Conclusions for Vietnam

The Global Status of Dugongs UNEP status report and action plan Covers 37 countries of dugongs’ range

Methods Evaluation based on published information and expert opinions of about 100 scientists and managers regarding 37 countries and territories in dugong’s range Snowball sampling technique Informants contacted during process leading to development of global status and action plan Information reviewed by 60 in-country experts.

Evidence for Decline Numbers have declined in at least 21 countries Dugongs are extinct in 3 island groups No evidence of reduction in extent of range - reduction of area of occupancy within range Dugong catch per unit effort in shark control nets on the urban coast of Queensland

Threats to Dugongs: Overview From 37 Countries THREATNO. OF COUNTRIES Fishing mortality (gill netting)at least 35 Habitat loss / Degradationall Hunting / Poachingat least 16 (27?) Boat Impactsat least 11

Dugongs tangle in mesh nets and accidentally drown in many countries

Habitat loss, especially due to extreme weather events 1000 km 2 of seagrass habitat were lost in Hervey Bay Queensland after two floods and a cyclone (hurricane )

Hunters and poachers kill dugongs in many countries Medical use of dugong products is a major reason for poaching and for killing animals which are caught accidentally in nets or fish traps

high risk of extinction reasonable prospects for survival uncertain prospects for survival high risk of extinction uncertain – likely extinction in Japan uncertain – likely extinction in Palau secure – except urban coast of Queensland

Prospects in SE Asia uncertain: likely extinction in Japan  Populations small and fragmented but cover vast areas with potential for recruitment from other areas  Pressure from gill-netting, dynamite fishing, habitat destruction, boat impacts and hunting likely to increase  Few effective conservation initiatives

Suggested approaches to dugong conservation Identify areas that still support significant numbers of dugongs Consider with extensive local involvement how dugong mortality can be minimised and their habitat protected If possible, protect dugongs in the context of comprehensive plans for coastal zone management using the dugong as a flagship species