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Sea mullet:

year-to-year changes in abundance

in the lower Hastings River

High flows Hastings from 1997.png
Sea mullet hastings.png
Low flows-96-onwards.png

 What is likely to explain these year-to-year changes (up to 2018)?

For Sea mullet of all sizes:

  • negative role of the duration of high flows in the previous month (see correlations below)

  • positive role of the duration of high flows in the previous year (see correlations below),

  • negative role of the duration of moderate flows in the previous year (see correlations below)

For adult Sea mullet:

  • positive role of the duration of high flows in the previous year (see correlations below),

  • negative role of the duration of very low flows in the previous year (see correlations below)

  • positive role of El nino tending conditions (see correlations below)

For juvenile Sea mullet:

  • positive role of the duration of high flows in the previous year (see correlations below),

  • negative role of the duration of moderate flows in the previous year (see correlations below)

  • positive role of flood flows in the pre-spawning migration period in the same year, and  two years before (see correlations below)

Hastings Sea mullet correlations.png
Flow data
Note that in the early stages of this investigation reliance was placed on Koree Island flow data provided by Port Macquarie and Hastings Council, data they are required to gather so to effectively provide environmental flows (EF) and to inform their own EF investigations.  The Council's last revision of the  flow rating curve for the site was in late 2015 and so data gathered subsequently, particularly after a major flood that occurred in March 2017, has questionable reliability due to possible channel-form changes. Accordingly,  additional reliance has been placed on flow data gathered further upstream at the Ellenborough gauging site. It is recognised that this data too has dubious reliability for understanding flow conditions in the lower river as  approximately 500 square kilometers of catchment is present between the Ellenborough gauging site and Koree Island near the tidal limit.

Abundance patterns within the lower river:

hastings-within-all-seamullet.png
Hastings-within-juv-seamullet.png
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