The distribution and abundance of the dugong in Shark Bay, Western Australia

1994 ◽  
Vol 21 (2) ◽  
pp. 149 ◽  
Author(s):  
H Marsh ◽  
RIT Prince ◽  
WK Saafeld ◽  
R Shepherd
Keyword(s):  
Western Australia ◽  
Large Scale ◽  
Correction Factors ◽  
Water Turbidity ◽  
Shark Bay ◽  
Northern Half ◽  
Perception Bias ◽  
Calving Rate ◽  
Specific Correction ◽  
Eastern Half

In July 1989, dugongs were counted from the air at an overall sampling intensity of 7.9% over 14 239 km2 in Shark Bay, Western Australia. Counts were corrected for perception bias (the proportion of dugongs visible in the transect that are missed by observers), and standardised for availability bias (the proportion of animals invisible because of water turbidity) with survey-specific correction factors. The resultant minimum population estimate was 10146 � 1665 (s.e.) dugongs at an overall density of 0.71 � 0.12 (s.e.) dugongs km-2, the highest density ever recorded on a large-scale dugong survey. The proportion of calves (19%) was higher than for most other dugong surveys conducted in Shark Bay and elsewhere, suggesting an exceptionally high calving rate in 1988. Dugong density was highest (>5 km-2) in relatively deep water (12-16 m) in the eastern half of Shark Bay opposite the tip of Peron Peninsula and in the western Bay opposite the northern half of Dirk Hartog Island. Fewer than 4% of dugongs sighted in Shark Bay during the survey were in waters colder than 18�C. Results of aerial surveys over 906 km2 in the Faure Sill region of the eastern Bay in November 1990 and January 1991 suggest that between a third and a half of the dugongs in Shark Bay are located in this region during the summer. In contrast, only one dugong was sighted there during the winter survey. The survey confirms that Shark Bay is an internationally significant dugong habitat.

Distribution and abundance of dugongs in Moreton Bay, Queensland, Australia

2003 ◽  
Vol 30 (4) ◽  
pp. 397 ◽  
Author(s):  
Janet M. Lanyon
Keyword(s):  
Hot Spots ◽  
Population Estimates ◽  
Correction Factors ◽  
Water Turbidity ◽  
Mean Intensity ◽  
Moreton Bay ◽  
Perception Bias ◽  
Species Specific ◽  
High Degree ◽  
Specific Correction

Dugong abundances in Moreton Bay (south-east Queensland) were estimated during six bi-monthly aerial surveys throughout 1995. Sampling intensity ranged between 20 and 80% for different sampling zones within the Bay, with a mean intensity of 40.5%. Population estimates for dugongs were corrected for perception bias (the proportion of animals visible in the transect that were missed by observers), and standardised for availability bias (the proportion of animals that were invisible due to water turbidity) with survey and species-specific correction factors. Population estimates for dugongs in Moreton Bay ranged from 503 ± 64 (s.e.) in July to 1019 ± 166 in January. The highest uncorrected count was 857 dugongs in December. This is greater than previous population estimates, suggesting that either previous surveys have underestimated abundance and/or that this population may have increased through recruitment, immigration, or a combination of both. The high degree of variation in population estimates between surveys may be due to temporal differences in distribution and herding behaviour. In winter, dugongs were found in smaller herds and were dispersed over a wider area than in summer. The Eastern Banks region of the bay supported 80–98% of the dugong population at any one time. Within this region, there were several dugong 'hot spots' that were visited repeatedly by large herds. These 'hot spots' contained seagrass communities that were dominated by species that dugongs prefer to eat. The waters of Rous Channel, South Passage and nearby oceanic waters are also frequently inhabited by dugongs in the winter months. Dugongs in other parts of Moreton Bay were at much lower densities than on the Eastern Banks.

Distribution and Abundance of Dugongs in the Northern Great Barrier-Reef Marine Park

1989 ◽  
Vol 16 (4) ◽  
pp. 429 ◽  
Author(s):  
H Marsh ◽  
WK Saalfeld
Keyword(s):  
Great Barrier Reef ◽  
Population Estimate ◽  
Seagrass Beds ◽  
Barrier Reef ◽  
Correction Factors ◽  
Water Turbidity ◽  
Density Estimates ◽  
Marine Park ◽  
Perception Bias ◽  
Specific Correction

In 1984 and 1985, dugongs were censused from the air at an overall sampling intensity of 9% over a total area of 31 288 km2 within the northern sections of the Great Barrier Reef Marine Park. Sightings were corrected for perception bias (the proportion of animals visible in the transect which are missed by observers), and availability bias (the proportion of animals that are invisible due to water turbidity) with survey-specific correction factors. There were no significant differences between population and density estimates obtained from repeat surveys of the same areas. The resultant population estimate (�s.e.) was 8110 � 1073 dugongs at an overall density (� s.e.) of 0.26�0.03 km-2, a precision of 13%. Dugongs occurred up to 58 km offshore and in water up to 37 m deep. The highest density of animals was seen on coastal seagrass beds at depths of <5 m. Maps of density and distribution are given. The design and timing of future surveys is also discussed.

Biology of modern Fragum erugatum (Mollusca, Bivalvia, Cardiidae) in relation to deposition of the Hamelin Coquina, Shark Bay, Western Australia

1997 ◽  
Vol 48 (5) ◽  
pp. 415 ◽  
Author(s):  
P. F. Berry ◽  
P. E. Playford
Keyword(s):  
Western Australia ◽  
Large Scale ◽  
Gill Tissue ◽  
Shell Shape ◽  
Size Distributions ◽  
Storm Events ◽  
Shark Bay ◽  
Scale Deposition

Fragum erugatum populations were sampled over two consecutive years in Hamelin Pool, Lharidon Bight and Freycinet Harbour, which are representative of the hypersaline and metahaline regimes of Shark Bay. F. erugatum was widely distributed infratidally between 1.2 m and 6.5 m depth. Dense aggregations of zooxanthellae were present in mantle and gill tissue. Shell shape of the population from Hamelin Pool differs from that of the Lharidon Bight, Freycinet Harbour and Dampier Archipelago populations. F. erugatum was found to be a synchronous hermaphrodite. Settlements of juveniles, and modality of size distributions, indicate a single annual spawning. Production estimates of dry flesh and shell (CaCO3 inclusive) were much lower in Hamelin Pool than in Lharidon Bight, largely because of the lower density of F. erugatum recorded in Hamelin Pool. Although shells are washed ashore continuously, large-scale deposition of the accumulated infratidal coquinas, largely composed of F. erugatum shells, probably occurs periodically in major storm events, thereby forming the Hamelin Coquina.

scholarly journals Large‐scale eDNA metabarcoding survey reveals marine biogeographic break and transitions over tropical north‐western Australia

2021 ◽  
Author(s):  
Katrina West ◽  
Michael J. Travers ◽  
Michael Stat ◽  
Euan S. Harvey ◽  
Zoe T. Richards ◽  
...  
Keyword(s):  
Western Australia ◽  
Large Scale ◽  
North Western

Integration of Cretaceous Morro do Chaves rock properties (NE Brazil) with the Holocene Hamelin Coquina architecture (Shark Bay, Western Australia) to model effective permeability

2016 ◽  
Vol 22 (2) ◽  
pp. 105-122 ◽  
Author(s):  
Patrick W. M. Corbett ◽  
Rayana Estrella ◽  
Andrea Morales Rodriguez ◽  
Ahmed Shoeir ◽  
Leonardo Borghi ◽  
...  
Keyword(s):  
Western Australia ◽  
Effective Permeability ◽  
Rock Properties ◽  
The Holocene ◽  
Shark Bay

Change in abundance of dugongs in Shark Bay, Ningaloo and Exmouth Gulf, Western Australia: evidence for large-scale migration

2004 ◽  
Vol 31 (3) ◽  
pp. 283 ◽  
Author(s):  
Nick Gales ◽  
Robert D. McCauley ◽  
Janet Lanyon ◽  
Dave Holley
Keyword(s):  
Marine Protected Areas ◽  
Large Scale ◽  
Population Demographics ◽  
Shark Bay ◽  
Ningaloo Reef ◽  
Aerial Surveys ◽  
Large Numbers ◽  
Plausible Hypothesis ◽  
Exmouth Gulf ◽  
Regional Abundance

The third in a series of five-yearly aerial surveys for dugongs in Shark Bay, Ningaloo Reef and Exmouth Gulf was conducted in July 1999. The first two surveys provided evidence of an apparently stable population of dugongs, with ~1000 animals in each of Exmouth Gulf and Ningaloo Reef, and 10 000 in Shark Bay. We report estimates of less than 200 for each of Exmouth Gulf and Ningaloo Reef and ~14 000 for Shark Bay. This is an apparent overall increase in the dugong population over this whole region, but with a distributional shift of animals to the south. The most plausible hypothesis to account for a large component of this apparent population shift is that animals in Exmouth Gulf and Ningaloo Reef moved to Shark Bay, most likely after Tropical Cyclone Vance impacted available dugong forage in the northern habitat. Bias associated with survey estimate methodology, and normal changes in population demographics may also have contributed to the change. The movement of large numbers of dugongs over the scale we suggest has important management implications. First, such habitat-driven shifts in regional abundance will need to be incorporated in assessing the effectiveness of marine protected areas that aim to protect dugongs and their habitat. Second, in circumstances where aerial surveys are used to estimate relative trends in abundance of dugongs, animal movements of the type we propose could lead to errors in interpretation.

Aerial Surveys of Sea Turtles in the Northern Great Barrier-Reef Marine Park

1989 ◽  
Vol 16 (3) ◽  
pp. 239 ◽  
Author(s):  
H Marsh ◽  
WK Saalfeld
Keyword(s):  
Great Barrier Reef ◽  
Sea Turtles ◽  
Analysis Of Covariance ◽  
Seagrass Beds ◽  
Barrier Reef ◽  
Sea State ◽  
Water Turbidity ◽  
Density Estimates ◽  
Marine Park ◽  
Specific Correction

In 1984 and 1985, during surveys designed primarily to census dugongs, six species of sea turtles were counted from the air at an overall sampling intensity of 9% over a total area of 31 288 km2 within the northern sections of the Great Barrier Reef Marine Park. The sea turtles were not identified to species. We attempted to correct sightings for perception bias (the proportion of animals visible in the transect which are missed by observers), and to standardise for availability bias (the.proportion of animals that are invisible due to water turbidity) with survey-specific correction factors. The resultant minimum population estimate in November 1985 was (mean � s.e.) 32 187 � 2532 sea turtles at an overall density of 1.03 � 0.08 km-2, a precision of 8%. We consider this to be a gross underestimate of numbers present. Significant differences between population and density estimates obtained from repeat surveys of the same areas were accounted for by differences in Beaufort sea state and cloud cover. The analysis of covariance data suggested that we had not been successful in standardising all biases. Turtles were widely distributed throughout the Great Barrier Reef lagoon from inshore seagrass beds to mid- and outer-shelf reefs. Highest densities were observed on inshore seagrass beds and on mid-shelf reefs, particularly between Murdoch Island and Cape Melville, and in Princess Charlotte Bay. Maps of density and distribution are given. We discuss the value and limitations of this survey regime for censusing sea turtles.

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