the dugong: a conservation challenge
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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 - PowerPoint PPT PresentationTRANSCRIPT
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The dugong: a conservation challenge
Helene Marsh and associates
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The modern sirenia (seacows)- dugongs and manatees
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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
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Global conservation status of modern sirenia
Antillean manatee vulnerableAmazonian manatee vulnerable
West African manatee vulnerableDugong vulnerableSteller’s sea cow extinct
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Distribution of modern Sirenia
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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
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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%
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Dugong feeding trail
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Seagrass specialists- coastal distribution, pollution, fishing mortality and boat strike
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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
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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
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Australian lineages reflect sea level changes
1
2
3
4
5
WA
NTTS
NQ
SQ
26ĮS
10ĮS
123ĮE 153ĮE
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Movements–>60 animals satellite tracked–most movements local–several animals made long-distance movements–longest movement ~800 km in few days
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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
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Dugongs visible from aircraft
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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
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Water turbidity affects dugong sightability
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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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-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
00 50 100 150 200 250 300
-10
-9
-8
-7
-6-5
-4
-3
-2
-1
00 20 40 60 80
-10
-9
-8
-7
-6-5
-4
-3
-2
-1
00 50 100 150 200
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
00 50 100 150
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
00 50 100 150 200 250 300
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
00 50 100 150 200
A B D
C2 C1 C
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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Block 1
0
500
1000
1500
2000
Block 2
0
500
1000
1500
2000
Block 3
0
500
1000
1500
2000
1986 1990 1994 1998
Block 4
0
500
1000
1500
2000
1986 1990 1994 1998
Total
0
500
1000
1500
2000
2500
1986 1990 1994 1998 Location of blocks and transects in Hervey Bay
Changes in dugong numbers in Hervey Bay Queensland
~2000 dugongs
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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
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Conclusion:
Aerial surveys are excellent for:determining dugong distribution and
relative abundance
But not for monitoring population change in Australia ? New Caledonia
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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)
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Location of shark meshingcontract areas
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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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••
••
•••
•
•
••
•••••
•••
••••••••••
•••••••••
1970 1980 1990 2000
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1960
Dug
ongs
cau
ght p
er m
onth
/ be
ach
The dugong by-catch declined at 8.7% p.a.
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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
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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
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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
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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
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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.
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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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Multiple impacts
Boat strikes
Net entanglementsHabitat loss from terrestrial runoff
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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
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High risk of extinction
Populations apparently small and fragmentedPressure from gill-netting, shark meshing, dynamite fishing and habitat destructionFew effective conservation initiatives
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Significant numbers of dugongsHuman population density and coastal impacts low in some areas
Reasonable prospects for survival
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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
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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
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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
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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
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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