Moresby Estuary

The area of the Moresby estuary reporting zone can be defined by the pre-cleared extent of mangrove and saltmarsh remnant vegetation which is characterised by species that require periodic inundation of sea water.

This area extends approximately 3.3 km north and 2 km south of the river mouth along the coastline and extends approximately 12 km inland. The area includes numerous tributaries that drain into the main river channel.

Land use within the Moresby estuary area is dominated by cropping and pond aquaculture with some residential development. The Moresby locality is on the western fringe of the estuary area. The Port of Mourilyan is located near the mouth of the estuary and exports raw sugar and molasses from a loader, wharf and handling facility.

The Moresby estuary grade has remained ‘good’ in 2019-20  with the score increasing slightly from 66 to 70. 

The diagram below shows the detailed results for each indicator by year. Click on the timeslider to see data from previous years.

Water quality

The Moresby estuary water quality improved to ‘very good’ with the score increasing slightly from 80 in 2018-19 to 83.

DIN (dissolved inorganic nitrogen) along with dissolved oxygen were the lowest scoring indicators (both 69) and were graded ‘good’, meaning monthly median values were often meeting guideline values.

Chlorophyll a, filterable reactive phosphorus (FRP) and turbidity were graded ‘very good’, with most monthly median values meeting guideline values.

Water quality grades are based on aquatic ecosystem guidelines for protection of estuarine waters and are not based on load reduction targets for the marine environment. The results are derived from a transect of five monitoring sites in the mid-estuary channels.

Pesticides are not monitored in the Moresby estuary therefore a score and grade cannot be provided.

Habitat and hydrology

The habitat and hydrology index is comprised of seagrass, which is updated annually, and three longer-term indicator categories that are updated every four years: mangrove and saltmarsh extent, riparian extent (both updated for 2018-19) and fish barriers (update due for 2020-21). The habitat and hydrology score improved from 54 in 2018-19 to 58 but remained ‘moderate’.

Mangrove and saltmarsh extent scored 79 (‘good’) with 5.9% loss from pre-clear to 2017.

Riparian extent scored 68 (‘good’) with 11.1% loss from pre-clear to 2017. There was no change to mangrove and saltmarsh extent and riparian extent between the previous assessment for 2013 and the updated assessment for 2017, however the updated Regional Ecosystem mapping (Version 5) resulted in a 2.1% reduction of the estimated loss of riparian extent from pre-clear which was set at 13.2% for 2013 .

Estuary fish barriers for the Moresby estuary scored 61 (‘good’) and were graded 'poor’ for barrier density, ‘good’ for percentage of stream length to the first barrier, and there was an absence of low passability barriers (graded ‘very good’).

The seagrass at the Moresby River improved from ‘very poor’ to ‘poor’ condition and the score increased from 8 in 2018-19 to 25. Seagrass was present at four of the five monitoring meadows for the second year in a row, following the complete collapse of seagrass at monitoring meadows in 2017-2018. The improved condition was mainly due to large biomass increases of Halophila at two of the meadows. There continues to be absence of Zostera muelleri, which was one of the key foundation species in the area before the collapse. A small-scale pilot of transplanted seagrass fragments has recently been conducted in Mourilyan (Moresby Estuary) by JCU. This trial showed successful survival and expansion of fragments over a 5-month period. The successful approach can now be applied at a larger scale. Seagrass condition will remain poor in Moresby estuary in the absence of restoration due to the lack of local propagules.

The flow indicator could not be assessed for the Moresby estuary due to the lack of pre-development modelled flow and flow assessment sites, which are required for the analysis.
development modelled flow and flow assessment sites, which are required for the analysis.

Fish

The fish index is currently under development and will be available in future report cards.

See the detailed reports for further information on the methods used to produce the scores and grades and detailed results.