The global status of dugongs

Conservation significance of dugongs

• Only member of family Dugongidae

• Only strictly marine herbivorous mammal

• Largest population size (>100,000) and range of extant Sirenians

Methods

• Evaluation based on published information and expert opinions of about 100 scientists and managers regarding 37 countries in dugong’s range

• Informants contacted 1997 - 2001 during process leading to development of global status and action plan

• Information reviewed by 60 in-country experts.

Dugongs are seagrass specialists

Dugong life history

• Lifespan < 70+ yr• Age first breeding 6-17yr• Gestation period 13-15 mth• Calving interval > 2.5 yr• Lactation ~ 1.5 yr• Adult survivorship >95%• Max rate of increase < 5%• Sustainable harvest ~2%

Conclusions

• 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

Preliminary information on genetics of female dugongs

• Genetic types of female dugongs from Southeast Asia (Indonesia, Thailand, Philippines generally distinct from those from Australia) - overlap at Ashmore Reef between Australia and Timor

• Two maternal lineages in Australian coastal waters - overlap in Torres Strait between Australia and Papua New Guinea

• One Australian lineage also recorded from East Africa and the Arabian Gulf

Movements

• Dugong– >60 animals satellite tracked– most movements local– several animals made long-distance

movements– longest movement ~800 km in few days– recent Aldabra sighting confirms capacity to

cross ocean trenches

Dugong Movements

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Maximum movement

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Dugongs have movement capacity to colonise areas of their range where they have been extirpated but probably do so rarely

Threats to dugongs- overview from 37 countries

Threat No. of countries

Fishing mortality At least 35

Habitat loss/degradation

All

Hunting/ poaching At least 16 ?27

Boat impacts At least 11

Dugongs tangle in mesh nets and accidentally drown in many countries

Habitat loss, especially due to extreme weather events

1000 km2 of seagrass habitatwere lost in Hervey Bay Queenslandafter two floods and a cyclone

Hunting and poaching kill dugongs in many countries

Evidence for dugong decline- 37 countries

• Anecdotal evidence suggests that dugong numbers have declined in at least 21 countries and that dugongs are extinct in 3 island groups

• No evidence of reduction in extent of range - reduction of area of occupancy within range

• Quantitative evidence of decline available only for Queensland, Australia

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1970 1980 1990 2000

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The dugong by-catch declined at 8.7% p.a. for 40 years

Urban coast of Queensland Australia - dugong CPUE in shark nets.

High risk of extinction

Populations apparently small and fragmentedPressure from gill-netting, shark meshing and habitat destructionFew effective conservation initiatives

Likely that region supports significant numbers of dugongsHuman population density and coastal impacts low on Saudi coast

Reasonable prospects for survival

Second largest dugong population in the world (7307+ s.e. 1302) Habitat threatened by coastal development and oil spillFew effective conservation initiatives

Uncertain prospects for survival

High risk of extinction

Populations apparently small, fragmented and isolatedPressure from gill-netting, dynamite fishing, habitat destruction and hunting likely to increaseFew effective conservation initiatives

Uncertain: likely extinction in Japan

Populations apparently small and fragmented. but cover vast areas with potential for recruitment from other areasJapanese population extremely small and isolated and subject to habitat loss and fishing impactsPressure from gill-netting, dynamite fishing, habitat destruction, boat impacts and hunting likely to increaseFew effective conservation initiatives

Uncertain: likely extinction in Palau

Populations apparently small and fragmented. Potential for recruitment from other areas uncertainPalau population extremely small and isolatedPressure from gill-netting, dynamite fishing, habitat destruction and hunting likely to increaseFew conservation initiatives

Secure except for urban coast of Qld

Region supports large numbers of dugongs (estimated population 85,000) Human population density and coastal impacts low except on urban coast of QueenslandPopulation changes confounded by large-scale movementsActive conservation initiatives, including dugong-specific actions along east coast of Queensland.

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