Shark Control Records Hindcast Serious Decline in Dugong Numbers off the Urban Coast of Queensland

Helene Marsh, Glenn De'ath, Neil Gribble and Baden Lane

FOREWORD [Adobe Acrobat Format 10.65KB]

PREFACE [Adobe Acrobat Format 12.57KB]

SUMMARY [Adobe Acrobat Format 10.35KB]

INTRODUCTION [Adobe Acrobat Format 28.01KB]

METHODS [Adobe Acrobat Format 20.40KB]

• Preparation of the Data for Statistical Modelling
• Statistical Analysis.

RESULTS [Adobe Acrobat Format 81.56KB]

• Temporal Changes in the Shark Control Program
• Factors with the Potential to Affect the Capture Rate of Dugongs
• The Profiles for Contract Areas
• The Overall Profile.

DISCUSSION [Adobe Acrobat Format 25.23KB]

• Explanations for the Decline in Dugong Catches in Shark Nets
  • Changes in the Practice of Shark Meshing?
  • Changes in the Behaviour of Dugongs in the Areas Fished by the Nets?
  • Catch Rates do not reflect Dugong Population Density?
• Is the Decline Plausible?
• Additional Evidence for a Decline in Dugong Numbers Along the Urban Coast of Queensland
• Implications for Management of the Dugong in Queensland
• Implications for Determining the Status of Other Long-lived Species.

ACKNOWLEDGMENTS [Adobe Acrobat Format 4.08KB]

REFERENCES [Adobe Acrobat Format 14.10KB]

FIGURES (Note: Access to figures is available through the Adobe Acrobat documents above)

1. Map showing the deployment of shark control nets along the eastern coast of Queensland
2. Sampling times for the 47 beaches within the eight contract areas used in the analyses
3. Temporal changes in the number of nets deployed by the Queensland Shark Safety Program
4. Partial effects plots for month adjusted for year, beach, number of nets and number of days fished on the number of dugongs caught in the Shark Control Program
5. Profiles of the annual estimated mean numbers of dugongs caught at each beach for each of six contract areas for the period 1962–1999 based on the reduced data set 
6. Profiles of the annual estimated mean numbers of dugongs caught per beach in each of the six contract areas for the period 1962–1999 for the reduced data set
7. Profile of the annual estimated mean numbers of dugongs caught for the period 1962–1999 for the reduced data set showing a strong overall decline in the number of dugongs caught per month per beach
8. Profiles of the annual estimated mean number of dugongs 
   1. Caught for the period 1962–1999 for the full data set with 95 per cent confidence bands, and the reduced data set Proportional rates of decline for the period 1962–1999 
   2. For all data and the reduced data set.

Dugong Distribution and Abundance in the Southern Great Barrier Reef Marine Park and Hervey Bay: Results of an Aerial Survey in October–December 1999

Helene Marsh and Ivan Lawler

SUMMARY [Adobe Acrobat Format 13.81KB]

INTRODUCTION [Adobe Acrobat Format 9.13KB]

METHODS [Adobe Acrobat Format 597.82KB]

• Survey Methodology
• Correction Factors
• Population Estimation
• Statistical Analysis.

RESULTS [Adobe Acrobat Format 1426.13KB]

• Group Size and Composition
  • Southern Great Barrier Reef
  • Hervey Bay
  • Moreton Bay
• Dugong Abundance
  • Southern Great Barrier Reef
  • Hervey Bay
  • Moreton Bay
• Dugong Protection Areas (DPAs)
  • Other Protection of Dugongs.

DISCUSSION [Adobe Acrobat Format 26.93KB]

• Temporal Changes in Dugong Distribution and Abundance
• An Evaluation of Explanations for the Observed Changes in Dugong Distribution and Abundance
  • Sighting Conditions
  • Experience of Observers
  • Changes in Dugong Fecundity
  • Dugong Movements
    • Within Surveys
    • Between Surveys
• Implications for Dugong Management: the Effectiveness of DPAs
• Implications for the Future of Dugong Surveys.

ACKNOWLEDGMENTS [Adobe Acrobat Format 4.00KB]

REFERENCES [Adobe Acrobat Format 11.32KB]

APPENDIX [Adobe Acrobat Format 36.32KB]

• Appendix Table 1. Beaufort sea state and glare for each transect
• Appendix Table 2. Raw data for sightings of dugong groups for each transect in each block used for population estimates
• Appendix Table 3. Raw data used for calculation of correction factors for dugongs for the survey

FIGURES (Note: Access to figures is available through the Adobe Acrobat documents above)

1a. Positions of blocks C9 to C12, and transects contained within, in the Central Section of the Great Barrier Reef region, from Innisfail to Magnetic Island

1b. Positions of blocks C1to C8, and transects contained within, in the Central Section of the Great Barrier Reef region, from Cleveland Bay to Repulse Bay

1c. Positions of blocks S6 to S8, and transects contained within, in the southern section of the Great Barrier Reef region, from the Newry Region to Clairview

1d. Positions of blocks S4 and S5, and transects contained within, in the southern section of the Great Barrier Reef region, from Shoalwater Bay to the northern end of Curtis Island

1e. Positions of blocks S1 to S3, and transects contained within, in the Southern Section of the Great Barrier Reef region, from Curtis Island to Baffle Creek

1f. Positions of blocks H1 to H5, and transects contained within, in the HerveyBay/Great Sandy Straits region 

1g. Positions of blocks M1-M6, and transects contained within, in Moreton Bay

2a. Estimated dugong abundance for the Central Section of the Great Barrier Reef region for four consecutive surveys in 1986–1987, 1992, 1994 and 1999

2b. Estimated dugong abundance for the Southern Section of the Great Barrier Reef region for four consecutive surveys in 1986–1987, 1992, 1994 and 1999

2c. Estimated dugong abundance for the Hervey Bay/Great Sandy Straits region for four consecutive surveys in 1992, 1993, 1994 and 1999

3a. Positions of dugong sightings in blocks C9 to C12 relative to Dugong Protection Areas and region zoning in the Central Section of the Great Barrier Reef region, from Innisfail to Magnetic Island

3b. Positions of dugong sightings in blocks C1 to C8 relative to Dugong Protection Areas and region zoning in the Central Section of the Great Barrier Reef region, from Cleveland Bay to Repulse Bay 

3c. Positions of dugong sightings in blocks S6 to S8 relative to Dugong Protection Areas and region zoning in the Southern Section of the Great Barrier Reef region, from the Newry Region to Clairview 

3d. Positions of dugong sightings in blocks S4 and S5 relative to Dugong Protection Areas and region zoning in the Southern Section of the Great Barrier Reef region, from Shoalwater Bay to the northern end of Curtis Island

3e. Positions of dugong sightings in blocks S1 to S3 relative to Dugong Protection Areas and region zoning in the Southern Section of the Great Barrier Reef region, from Curtis Island to Baffle Creek 

3f. Positions of dugong sightings in blocks H1 to H5 relative to Dugong Protection Areas and Marine Park zoning in the Hervey Bay/Great Sandy Straits region

3g. Positions of dugong sightings in blocks M1–M6 in Moreton Bay

TABLES

1. Modification of the survey design from previous surveys, mainly as a result of poor weather conditions encountered during the surveys 
2. Weather conditions encountered during the survey in comparison to previous surveys of the same areas
3. Areas of survey blocks and sampling intensities 
4. Details of groups size estimates and correction factors used in the population estimates for dugongs in the 1999 survey of the southern Great Barrier Reef region and Hervey Bay
5. Estimate of dugong numbers for each survey block in the region between Innisfail and Moreton Bay
6. Sumary of Restricted Maximum Likelihood analyses comparing dugong densities across consecutive surveys
7. Percentages of dugongs in southern Great Barrier Reef region and Hervey Bay region found in Dugong Protection Areas (DPAS) in 1999 based on mean population estimates
8. The estimated proportion of dugongs occurring in DPAs in the southern Great Barrier Reef on the basis of the large-scale surveys conducted in 1992, 1994 and 1999 based on mean population estimates.
    

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