The dugong: a conservation challenge

Helene Marsh and associates

The modern sirenia (seacows)- dugongs and manatees

Biodiversity importance of Order Sirenia

• 2 families– Trichechidae

• Antillean manatee Trichechus manatus• Amazonian manatee Trichechus inunguis• West African manatee Trichechus senegalensis

– Dugongidae• Dugong Dugong dugon• Steller’s sea cow Hydrodamalis gigas

Global conservation status of modern sirenia

Antillean manatee vulnerableAmazonian manatee vulnerable

West African manatee vulnerableDugong vulnerableSteller’s sea cow extinct

Distribution of modern Sirenia

Conservation significance of dugongs

• One of only four members of order Sirenia

• Only member of family Dugongidae

• Only strictly marine herbivorous mammal

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

Long-lived, slow breeding

• 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%

Dugong feeding trail

Seagrass specialists- coastal distribution, pollution, fishing mortality and boat strike

Restricted coastal habitat subject to large-scale diebacks

e.g. 1000 km2 of seagrass habitatwere lost in Hervey Bay Queenslandafter two floods and a cyclone but also in several pristine and remote areas

Preliminary information on genetics of female dugongs :

mitochondrial DNA• Mitochondrial DNA of dugongs from Southeast Asia

generally distinct from those from Australia

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

• High haplotypic (h=0.97)and nucleotide (=2.3) diversity

• No data from Pacific Islands

Australian lineages reflect sea level changes

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NTTS

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26ĮS

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123ĮE 153ĮE

Movements–>60 animals satellite tracked–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

• 5-551 days• Individual movements

variable even for animals caught together

– Covered over 80% of coast

– 1/3 moved linear distances >80km

– 1/6 moved >150km

1500km

280km

400km

Shoalwater Bay

Cooktown

Townsville

Dugongs visible from aircraft

Objective of aerial surveys: To monitor dugong distribution &

relative abundance over large spatial and temporal scales

Standardised technique

– Corrections for bias– Strict ceiling on weather– Conducted over large spatial scales

(30,000 km2) every 5 years since mid 1980s

– Different survey regions surveyed in different years

Time series since mid 1980s

Water turbidity affects dugong sightability

Models fitted with timed depth recorders were raised from the bottom until they become visible from a helicopter at aerial survey height

Correction for animals which can’t be seen in turbid water

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Zone of non-availability

Dugong dive profiles

~40,000 dives from 15 dugongsEstimation of the proportion of dugongs

missed in water of varying turbidity:estimates of absolute abundance

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1986 1990 1994 1998 Location of blocks and transects in Hervey Bay

Changes in dugong numbers in Hervey Bay Queensland

~2000 dugongs

Similar patterns of large scale movement

• Torres Strait• Cape York coast of Great Barrier Reef • Urban coast of Great Barrier Reef• Shark Bay – Exmouth Gulf in Western

Australia

Conclusion:

Aerial surveys are excellent for:determining dugong distribution and

relative abundance

But not for monitoring population change in Australia ? New Caledonia

Monitoring change over 40 years using CPUE

•In 1962, the Queensland government beganthe Shark Control Program aimed at reducing shark numbers at popular bathing beaches

•Nets used to catch sharks also catch marine mammals including dugongs

•Analysed temporal changes in the dugong catch per beach from 1962-99 as an index of changes in dugong abundance (in response to ALL influences)

Location of shark meshingcontract areas

Assumptions•Netting practice did not change

•Catch rate of dugongs was proportional •to population size ?

•Dugongs did not learn to avoid nets ?

•Dugongs were not alienated from netted beaches by human use ???

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

If assumptions are correct, dugongs numbers on the urban coast of Qld in the local regions of the shark nets have declined to about 3% of their 1960 value

Conclusion

Response to dugong decline in Queensland

• Moratorium on hunting on urban coast

• 16 Dugong Protection Areas (6353 km2)– no gill-netting (red)– gill-netting with

restrictions (yellow)• Restructuring of

fishing industry - buyout of fishers

Dugong behaviour from a blimp-mounted video camera

• THE BLIMP-CAM

• Tethered helium filled blimp/balloon

• Mounted remote control video camera

• Monitor on boat to view video image

• Digital video recorder on boat

BEHAVIOURAL DATA

Individual behaviour & herd behaviour

- ethogram and time budget

- dive and surfacing times

- mother/calf interactions

- herd size, composition, relative orientation & effects of habitat

OBJECTIVE

To determine the effects of boat noise on dugong behaviour

•opportunistically

•controlled experiments

PRELIMINARY RESULTS:

•Response is slow, particularly to boats going fast - may be run over before having time to move

• Dugongs usually move up to 3-400 m away and resume their original activity

Global Status: 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.

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

Multiple impacts

Boat strikes

Net entanglementsHabitat loss from terrestrial runoff

Threats to dugongs- overview from 37 countriesThreat No. of countries Fishing mortality At least 34 Habitat loss /degradation

At least 36

Hunting/poaching (Chinese medicine)

At least 26

Boat impacts At least 13

High risk of extinction

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

Significant numbers of dugongsHuman population density and coastal impacts low in some areas

Reasonable prospects for survival

Uncertain: likely extinction in Japan

Populations small and fragmented. Japanese 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

Probably secure except for urban coast and some heavily hunted areas

Region supports large numbers of dugongs (estimated 85,000) Remote: human population density and coastal impacts generally low Population changes confounded by large-scale movementsActive conservation initiatives, including dugong-specific actions in Great Barrier Reef region

Pacific Islands: Uncertain future

Populations apparently mostly small and fragmented. Potential for recruitment from other areas uncertainPressures likely to increaseFew conservation initiativesNew Caledonia very important

Conclusions• Total global population ~ 100,000 dugongs• Long-lived slow breeding • Seagrass specialist• Declines in most parts of range – multiple impacts• New Caledonia with significant, relatively

undisturbed lagoonal seagrass habitats and no gill netting - important for dugong conservation near eastern limit of range

• New Caledonia dugongs special -use reefal habitats, including outer edge of barrier reef

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 (hunting/poaching in New Caledonia) 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