Freshwater mullet:
year-to-year changes in abundance
in the lower Hastings River
What is likely to explain these year-to-year changes (up to 2018)?
For Freshwater mullet of all sizes:
-
positive role of the duration of higher flows in the previous month (see correlations below)
-
negative role of the duration of moderate flows in the previous month (see correlations below)
-
positive role of the duration of low flows in the previous year (see correlations below)
-
negative role of the duration of moderate-high flows in the previous year (see correlations below)
For adult Freshwater mullet:
-
positive role of the duration of lower flows in the previous month (see correlations below)
-
negative role of the duration of moderate-high flows in the previous month (see correlations below)
-
positive role of El nino tending conditions (see correlations below)
For juvenile Freshwater mullet:
-
positive role of the duration of higher flows in the previous month (see correlations below)
-
negative role of the duration of moderate flows in the previous month (see correlations below)
-
positive role of the duration of lower flows in the previous year (see correlations below)
-
negative role of the duration of moderate-high flows in the previous year (see correlations below)
-
(Surprisingly!) negative role of flood flows in the breeding season (December-April) in the year before (see correlations below)
-
(Surprisingly!) negative role of flood flows in the pre-spawning migration period (February-March) in the year before and the year before that (see correlations below)
-
positive role of El nino tending conditions (see correlations below)
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:
