Cockcroft, V.,Guissamulo, A.,Findlay, K.
Dugongs (Dugong dugon) of the Bazaruto Archipelago, Mozambique Technical Report
no. 72, 2008, ISBN: Final Report to SASOL Mozambique.
Abstract | BibTeX | Tags: abundance, Distribution, dugong, East Africa, Mozambique
@techreport{,
title = {Dugongs (Dugong dugon) of the Bazaruto Archipelago, Mozambique},
author = {Cockcroft, V.,Guissamulo, A.,Findlay, K.},
issn = {Final Report to SASOL Mozambique},
year = {2008},
date = {2008-01-01},
number = {72},
pages = {1-84},
abstract = {Historically, dugongs occurred in almost all coastal areas from southern Mozambique in the
west to Australia in the east, including many of the island States in the Indian and Pacific
Oceans between. However, through much of this range, dugongs have all but disappeared
and where they occur, are represented by relict populations. This is especially true for
Eastern Africa and the Indian Ocean and Mascerine Islands. In most areas dugongs have
been extirpated and only in southern, central Mozambique, the Bazaruto Archipelago, does a
relatively large number still survive.
Between April 2006 and December 2007 a series of 27 aerial surveys was flown over the
Bazaruto Bay region, from Cabo Sao Sebastio in the south to north of the Save River Mouth
in the north and between the coast and the 30 m isobath (extending to eastwards of the
Bazaruto Archipelago islands in the south). A total of 9052 nautical miles of survey was flown
during the 27 surveys. During these, 355 sightings of an estimated 760 dugongs were made.
Two core areas of distribution were apparent; a northern core region, between the Save River
Mouth and 21°24’ S, and a southern core region aligned with the shallow sandbanks to the
north and south of Santa Carolina Island. The mean group size of dugongs encountered was
2.22 and comparable to mean group sizes observed elsewhere. However, the maximum
group size observed was considerably smaller than those observed in other areas of dugong
abundance. Likewise, calculated dugong densities were substantially lower in the Bazaruto
area than they are in the Arabian Gulf or Australia. There was no evidence of any seasonal
variation in occurrence, group size, density or proportion of calves. The proportion of calves
was similar to that in other areas surveyed for dugongs.
Statistical manipulation of the data from aerial surveys suggests that the dugong population
inhabiting the area surveyed is around 250 animals.
The extent of dugong habitat was gauged by mapping seagrass occurrence, diversity and
distribution. Mapping was accomplished through extensive dive sampling of 982 stations
within the surveyed area, within 5m to about 25 m depth. Five species of seagrass were
identified within the area. These covered some 4.68 % of the area and occurred generally in
the north and close to the shore in waters less than 8 m deep. In the north, the areas of
greatest seagrass abundance and diversity coincide with the areas of greatest dugong
abundance. However, in the area to the north and south of Santa Carolina, seagresses were
almost absent, suggesting that this area is used by dugongs for reasons other than feeding.
Population Viability Analysis (PVA) modelling was used to assess the viability of the dugong
population in the Bazaruto Archipelago under various scenarios. PVA is a statistical method
of understanding the influence of a species’ natural history, in combination with demographic,
environmental, and random genetic (stochastic) events, on the dynamics of its future. The
species’ population dynamics is modelled as a set of discrete, sequential events (e.g., births,
deaths, catastrophes, etc.), which occur according to defined probabilities. Population
dynamics models provide a predictive tool, where the impacts of variables (threats), in this
instance – environmental threats (cyclones, floods); hydrocarbon exploration and incidental
fishing catch, can be theoretically modelled.
Overall, the PVA models suggest strongly that the dugongs inhabiting Bazaruto Bay are in a
precarious position and face extirpation. The models suggest that dugongs are particularly
susceptible to long term stressors that might reduce overall reproductive success. Further, the
analyses clearly show that regular deaths, from anthropogenic sources, are the major cause
of dugong decline.
A number of scenarios, covering options for hydrocarbon exploration and exploitation, are
presented and discussed, in terms of their potential impacts on the dugongs inhabiting the
Bazaruto area.},
keywords = {abundance, Distribution, dugong, East Africa, Mozambique},
pubstate = {published},
tppubtype = {techreport}
}
Historically, dugongs occurred in almost all coastal areas from southern Mozambique in the
west to Australia in the east, including many of the island States in the Indian and Pacific
Oceans between. However, through much of this range, dugongs have all but disappeared
and where they occur, are represented by relict populations. This is especially true for
Eastern Africa and the Indian Ocean and Mascerine Islands. In most areas dugongs have
been extirpated and only in southern, central Mozambique, the Bazaruto Archipelago, does a
relatively large number still survive.
Between April 2006 and December 2007 a series of 27 aerial surveys was flown over the
Bazaruto Bay region, from Cabo Sao Sebastio in the south to north of the Save River Mouth
in the north and between the coast and the 30 m isobath (extending to eastwards of the
Bazaruto Archipelago islands in the south). A total of 9052 nautical miles of survey was flown
during the 27 surveys. During these, 355 sightings of an estimated 760 dugongs were made.
Two core areas of distribution were apparent; a northern core region, between the Save River
Mouth and 21°24’ S, and a southern core region aligned with the shallow sandbanks to the
north and south of Santa Carolina Island. The mean group size of dugongs encountered was
2.22 and comparable to mean group sizes observed elsewhere. However, the maximum
group size observed was considerably smaller than those observed in other areas of dugong
abundance. Likewise, calculated dugong densities were substantially lower in the Bazaruto
area than they are in the Arabian Gulf or Australia. There was no evidence of any seasonal
variation in occurrence, group size, density or proportion of calves. The proportion of calves
was similar to that in other areas surveyed for dugongs.
Statistical manipulation of the data from aerial surveys suggests that the dugong population
inhabiting the area surveyed is around 250 animals.
The extent of dugong habitat was gauged by mapping seagrass occurrence, diversity and
distribution. Mapping was accomplished through extensive dive sampling of 982 stations
within the surveyed area, within 5m to about 25 m depth. Five species of seagrass were
identified within the area. These covered some 4.68 % of the area and occurred generally in
the north and close to the shore in waters less than 8 m deep. In the north, the areas of
greatest seagrass abundance and diversity coincide with the areas of greatest dugong
abundance. However, in the area to the north and south of Santa Carolina, seagresses were
almost absent, suggesting that this area is used by dugongs for reasons other than feeding.
Population Viability Analysis (PVA) modelling was used to assess the viability of the dugong
population in the Bazaruto Archipelago under various scenarios. PVA is a statistical method
of understanding the influence of a species’ natural history, in combination with demographic,
environmental, and random genetic (stochastic) events, on the dynamics of its future. The
species’ population dynamics is modelled as a set of discrete, sequential events (e.g., births,
deaths, catastrophes, etc.), which occur according to defined probabilities. Population
dynamics models provide a predictive tool, where the impacts of variables (threats), in this
instance – environmental threats (cyclones, floods); hydrocarbon exploration and incidental
fishing catch, can be theoretically modelled.
Overall, the PVA models suggest strongly that the dugongs inhabiting Bazaruto Bay are in a
precarious position and face extirpation. The models suggest that dugongs are particularly
susceptible to long term stressors that might reduce overall reproductive success. Further, the
analyses clearly show that regular deaths, from anthropogenic sources, are the major cause
of dugong decline.
A number of scenarios, covering options for hydrocarbon exploration and exploitation, are
presented and discussed, in terms of their potential impacts on the dugongs inhabiting the
Bazaruto area.
west to Australia in the east, including many of the island States in the Indian and Pacific
Oceans between. However, through much of this range, dugongs have all but disappeared
and where they occur, are represented by relict populations. This is especially true for
Eastern Africa and the Indian Ocean and Mascerine Islands. In most areas dugongs have
been extirpated and only in southern, central Mozambique, the Bazaruto Archipelago, does a
relatively large number still survive.
Between April 2006 and December 2007 a series of 27 aerial surveys was flown over the
Bazaruto Bay region, from Cabo Sao Sebastio in the south to north of the Save River Mouth
in the north and between the coast and the 30 m isobath (extending to eastwards of the
Bazaruto Archipelago islands in the south). A total of 9052 nautical miles of survey was flown
during the 27 surveys. During these, 355 sightings of an estimated 760 dugongs were made.
Two core areas of distribution were apparent; a northern core region, between the Save River
Mouth and 21°24’ S, and a southern core region aligned with the shallow sandbanks to the
north and south of Santa Carolina Island. The mean group size of dugongs encountered was
2.22 and comparable to mean group sizes observed elsewhere. However, the maximum
group size observed was considerably smaller than those observed in other areas of dugong
abundance. Likewise, calculated dugong densities were substantially lower in the Bazaruto
area than they are in the Arabian Gulf or Australia. There was no evidence of any seasonal
variation in occurrence, group size, density or proportion of calves. The proportion of calves
was similar to that in other areas surveyed for dugongs.
Statistical manipulation of the data from aerial surveys suggests that the dugong population
inhabiting the area surveyed is around 250 animals.
The extent of dugong habitat was gauged by mapping seagrass occurrence, diversity and
distribution. Mapping was accomplished through extensive dive sampling of 982 stations
within the surveyed area, within 5m to about 25 m depth. Five species of seagrass were
identified within the area. These covered some 4.68 % of the area and occurred generally in
the north and close to the shore in waters less than 8 m deep. In the north, the areas of
greatest seagrass abundance and diversity coincide with the areas of greatest dugong
abundance. However, in the area to the north and south of Santa Carolina, seagresses were
almost absent, suggesting that this area is used by dugongs for reasons other than feeding.
Population Viability Analysis (PVA) modelling was used to assess the viability of the dugong
population in the Bazaruto Archipelago under various scenarios. PVA is a statistical method
of understanding the influence of a species’ natural history, in combination with demographic,
environmental, and random genetic (stochastic) events, on the dynamics of its future. The
species’ population dynamics is modelled as a set of discrete, sequential events (e.g., births,
deaths, catastrophes, etc.), which occur according to defined probabilities. Population
dynamics models provide a predictive tool, where the impacts of variables (threats), in this
instance – environmental threats (cyclones, floods); hydrocarbon exploration and incidental
fishing catch, can be theoretically modelled.
Overall, the PVA models suggest strongly that the dugongs inhabiting Bazaruto Bay are in a
precarious position and face extirpation. The models suggest that dugongs are particularly
susceptible to long term stressors that might reduce overall reproductive success. Further, the
analyses clearly show that regular deaths, from anthropogenic sources, are the major cause
of dugong decline.
A number of scenarios, covering options for hydrocarbon exploration and exploitation, are
presented and discussed, in terms of their potential impacts on the dugongs inhabiting the
Bazaruto area.
Wilson,S.C.,Klaus,R.
The Gulf of Aden Book
Pergamon, Elsevier Science, 2000.
Abstract | BibTeX | Tags: Arabian Sea, conservation, coral, dolphin, dolphins, East Africa, enforcement, Fisheries, Gulf of Aden, Indian Ocean, management, marine, mortality, oceanography, Oman, pollution, productivity, Red Sea, turtles
@book{,
title = {The Gulf of Aden},
author = {Wilson,S.C.,Klaus,R.},
year = {2000},
date = {2000-01-01},
journal = {Seas at the Millennium: an Environmental Evaluation: Volume II Regional Chapters: The Indian Ocean to the Pacific},
number = {510},
pages = {47-61},
publisher = {Pergamon, Elsevier Science},
abstract = {The Gulf of Aden lies between southern Arabia and the Horn of Africa and connects with the Red Sea and Indian Ocean. The Socotra Archipelago lies at its entrance, off the Horn of Africa. The largest influence comes from the reversing monsoon system with strong and persistent winds that blow from the southwest in summer, and from the northeast in winter. These also cause a reversal in the direction of surface currents. Associated with the summer monsoon are upwelling areas along the eastern coast of Yemen, and one centred on the Somali coast southwest of Socotra. Both have a profound effect on coastal habitats and stimulate high marine productivity which supports a rich fishery. Marine biodiversity is relatively high since the area is a transition zone between the Red Sea, Southern Arabia and East Africa. Terrestrial diversity, particularly in the flora of Socotra, is also elevated by high levels of endemism. Coasts are mainly exposed sandy beaches separated by rocky headlands. Coral communities and reefs have developed most notably in Djibouti and offshore islands of Somalia. Seagrasses are relatively uncommon, and mangrove stands are most abundant to the west and southwest. A striking feature of rocky shores is the abundant macroalgae that appears following the onset of the Southwest Monsoon in particular. Green turtles nest in tens of thousands, and thousands of dolphins have also recently been observed. Perhaps the most serious single threat to sustainable use of marine resources comes from overfishing, particularly by industrial fleets that operate with or without licenses. Some stocks have collapsed or are showing signs of strain, including cuttlefish, shark and lobster. Wildlife species are also harvested and incidental mortality appears high. Levels of pollution are low except around larger towns where sewage and solid wastes are starting to affect resources. Chronic oil pollution originating from tankers is also cause for concern, but levels appear to be low. Harsh environmental conditions and lack of infrastructure limits exploitation of coastal resources and traditional methods of limiting exploitation are still effective. Political instability and unrest, and lack of funding have hampered coastal management, though a strategic action plan for the conservation and protection of the marine environment has recently been prepared by PERSGA as a crucial first step. There are only two small marine parks in the region, both in Djibouti.},
keywords = {Arabian Sea, conservation, coral, dolphin, dolphins, East Africa, enforcement, Fisheries, Gulf of Aden, Indian Ocean, management, marine, mortality, oceanography, Oman, pollution, productivity, Red Sea, turtles},
pubstate = {published},
tppubtype = {book}
}
The Gulf of Aden lies between southern Arabia and the Horn of Africa and connects with the Red Sea and Indian Ocean. The Socotra Archipelago lies at its entrance, off the Horn of Africa. The largest influence comes from the reversing monsoon system with strong and persistent winds that blow from the southwest in summer, and from the northeast in winter. These also cause a reversal in the direction of surface currents. Associated with the summer monsoon are upwelling areas along the eastern coast of Yemen, and one centred on the Somali coast southwest of Socotra. Both have a profound effect on coastal habitats and stimulate high marine productivity which supports a rich fishery. Marine biodiversity is relatively high since the area is a transition zone between the Red Sea, Southern Arabia and East Africa. Terrestrial diversity, particularly in the flora of Socotra, is also elevated by high levels of endemism. Coasts are mainly exposed sandy beaches separated by rocky headlands. Coral communities and reefs have developed most notably in Djibouti and offshore islands of Somalia. Seagrasses are relatively uncommon, and mangrove stands are most abundant to the west and southwest. A striking feature of rocky shores is the abundant macroalgae that appears following the onset of the Southwest Monsoon in particular. Green turtles nest in tens of thousands, and thousands of dolphins have also recently been observed. Perhaps the most serious single threat to sustainable use of marine resources comes from overfishing, particularly by industrial fleets that operate with or without licenses. Some stocks have collapsed or are showing signs of strain, including cuttlefish, shark and lobster. Wildlife species are also harvested and incidental mortality appears high. Levels of pollution are low except around larger towns where sewage and solid wastes are starting to affect resources. Chronic oil pollution originating from tankers is also cause for concern, but levels appear to be low. Harsh environmental conditions and lack of infrastructure limits exploitation of coastal resources and traditional methods of limiting exploitation are still effective. Political instability and unrest, and lack of funding have hampered coastal management, though a strategic action plan for the conservation and protection of the marine environment has recently been prepared by PERSGA as a crucial first step. There are only two small marine parks in the region, both in Djibouti.