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Shark control records hindcast serious decline in dugong numbers off the urban coast of Queensland

Shark control records hindcast serious decline in dugong numbers off the urban coast of Queensland. Helene Marsh, Glenn De'ath, JCU Neil Gribble and Baden Lane, QDPI. “ Of all the resources of Queensland waters, none is so extensive or valuable as its flocks of dugong”

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Shark control records hindcast serious decline in dugong numbers off the urban coast of Queensland

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  1. Shark control records hindcast serious decline in dugong numbers off the urban coast of Queensland Helene Marsh, Glenn De'ath, JCU Neil Gribble and Baden Lane, QDPI.

  2. “Of all the resources of Queensland waters, none is so extensive or valuable as its flocks of dugong” Thorne (1876) The queen of the colonies- early history of Queensland Australia

  3. Background • In 1962, the Qld government introduced the • Shark Control Program aimed at reducing • shark numbers at popular bathing beaches • Nets used to catch sharks also catch marine • mammals including dugongs • We 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)

  4. Location of shark meshing contract areas

  5. 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 ???

  6. Methods • General Linear Models analysed data from: • 47 beaches from 8 contract areas (full data set) • 31 beaches from the 6 areas where nets were • deployed for at least 8 years (reduced data set)

  7. Sampling times for beaches used in analyses. The reduced data set was based on beaches represented by solid lines.

  8. Temporal changes in dugong by-catch at six locations

  9. The dugong by-catch declined at 8.7% p.a. (reduced data set) The decline for the full data set was 8.2% p.a.

  10. Conclusion If our 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 values Is this decline plausible? Anecdotal information says yes at least in some areas

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