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Dugong biology: the case for a CMS

agreement

Dugong biology: the case for a CMS

agreementHelene Marsh

James Cook University AustraliaHelene Marsh

James Cook University Australia

Conservation significance of dugongs

• Only member of family Dugongidae

• Only strictly marine herbivorous mammal

• Largest population size and range of extant Sirenia(dugong and manatees)

• Currently classified as vulnerable at global scale by IUCN

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• High cultural value in many parts of range

• Valued source of food, medicine and artefacts in many countries

• Flagship species for coastal peoples

Cultural importance of dugongs

Convention for conservation of migratory species

• Objective:– To conserve terrestrial, avian and marine

species over the whole of their migratory range.

• Recognition of the need for countries to cooperate in conserving animals which migrate across national boundaries or between national territorial waters and the high seas.

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Extent of occurrence : 140,000 km of coastline across 48 countries

Still present at extreme ends of range but reduction in area of occupancy within range

from World Resource Institute

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Dive computers show dugongs spend most of their time feeding in shallow water < 10m,

72% dives< 3m

Seagrass specialist

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Area of occupancy: shallow coastal waters

potentially > 125,800 km2

Area of occupancy: shallow coastal waters

potentially > 125,800 km2

Critical habitat seagrass beds < 10mespecially <3m

Critical habitat seagrass beds < 10mespecially <3m

Dugongs farm seagrass – when dugongs are lost from an area it

may decline in habitat quality

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Space age technology to study dugong movements and diving

Acknowledgment James Sheppard

Small-scale commuting movements

Each colour an individual dugong

Each dot a location fix

Dugongs target specific areas with high biomass of preferred seagrass species

Acknowledgment James Sheppard

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Long distance movements:

Moves common yet unpredictable 44/72 >30km; 14>100kmAll size/age/sex classes make large-scale movesMoves up to 500km in 12 daysSome make return trips

Deep dives while traveling

Acknowledgment James Sheppard

Thermoregulatory movements at high latitude limits to range

Acknowledgment James Sheppard

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Occasionally cross ocean trenches

Maximum age > 70 years

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First breeds at age 6-17 years suckles young for up to 18 months

Acknowledgment Amanda Hodgson

One calf every 2.5 to 7 years depending on food supply

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If food supply is damaged dugongs postpone breeding and/or move

0

5

10

15

20

25

0 - 5 6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-50 51-55 >55

Age Class (years)

Num

ber o

f dug

ongs

Impact of seagrass dieback 20- 25 years previous in age structure of sample

Pregnancy Rate

1978-79 0.091979-80 0.191980-81 0.241998-99 0.38

Acknowledgment Donna Kwan

Cause of 1992 decline (emigration + mortality): Habitat loss, due to

extreme weather

1000 km2 of seagrass habitatwere lost in Hervey Bay in 1992after two floods and a cyclone

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After large scale seagrass loss dugongs move or delay breeding

Recovery of dugong carcasses after Hervey Bay seagrassloss

?

Acknowledgment Alana Grech

Habitat extends across international boundaries

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Biological scale? Clues from mTDNA

Restricted lineage

Widespread lineage

Outside Australia

Acknowledgment to Brenda McDonald

Biological scale? Clues from mTDNA but uncertainty remains

Widespread lineage

Restricted lineage

Acknowledgment to Brenda McDonald

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• Preliminary data from markers inherited from both parents consistent with isolation by distance at scale of hundreds of km

Microsatelitte markers

Scale Mismatches• Occur if mismatch between geo-political scale(s)

at which resource managed and biological scale at which resource functions

• Major impediment to successful management

Dugong with a range of 140,000 km of coastline

across 48 countries is at high

risk of scale mismatch

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Question?Is there a scale mismatch between the scale at which risks to dugongs from anthropogenic impacts are managed in the Great Barrier Reef region and the scale at which dugong populations function?

GBRWHA 348,000 km2

ecosystem level planning

5 scales in Great Barrier Reef World Heritage Area

Geo-political Biological 1 Biological 2 Biological 3 Local

GBRWHA (community)

uncertainty

Acknowledgment Alana Grech

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Spatial model of dugong distribution and abundance based on 20 years of aerial surveys

2.0 0.5 2.5 1.5 1.0 0.0

200

1000

800

600

400

Density of dugongs/km2

Freq

uenc

y (n

umbe

r of D

MU

s)

Acknowledgment Alana Grech

Two major sources of anthropogenic mortality

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Layers in 2x2 km grid

MPA Zoning Gillnetting Hunting

Dugong conservationvalue Total area of

GBRWHA348,000 km 2

Acknowledgment Alana Grech

Netting Conducted

Hunting Conducted

Acknowledgment Alana Grech

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38Local

38Biological 3

33Biological 2

41Biological 1

44Geo-political

Netting AllowedScale

100

100

100

100

100

Hunting Allowed

23

20

27

28

30

Hunting Conducted

38

38

33

41

44

Netting and unting

Allowed

1

0

0

4

4

Netting and Hunting

Conducted

% of area of high and medium Dugong Conservation Value

No evidence of scale mismatch because environmental planning in Great Barrier Reef region done at ecosystem scale

Acknowledgment Alana Grech

9

4

1

6

7

Netting Conducted

Conclusions• Dugongs need to be managed at

biological scales of hundreds of km• Most geo-political scales are much smaller

than this• Spatial scale mismatch is a serious

impediment to successful management • Spatial scale mismatch can be prevented

by ecosystem scale management planning• CMS MOU is significant advance

Thanks to:

Amanda HodgsonDonna Kwan

Brenda McDonaldAlana GrechRob Coles

James Sheppard