How Important Are Freshwater Flows for Gulf Estuaries?

How important are freshwater flows for Gulf estuaries? A study of the effect on food supply for migratory shorebirds Prof Michele Burford Australian Rivers Institute Griffith University Acknowledgements Water development is occurring in Gulf rivers - Flinders, Gilbert and Mitchell Rivers

• How will water development impact on the food supply for migratory shorebirds? • Can we get more recent data on shorebird numbers? Mitchell River

Gilbert River Flinders River

Watts/m Mean annual flow

Mitchell R.

d) Mitchell Flow (GL) Flow

e) Gilbert Gilbert R. Flow (GL) Flow

f) Flinders

Flow (GL) Flow Flinders R. Flow (GL) Flow

Year Year Broadley et al. Ecosphere Importance of southern Gulf for shorebirds

• 2nd most important shorebird site of International importance in Australia • 50% (ca. 2,000,000) use Gulf from Oct-March • Endangered & critically endangered species Historical knowledge

• 1998 survey including Flinders R surveys Gilbert & Mitchell R 1998-2013 areas

Driscoll 2014 Water = nutrients = food in the mud = birds

Surveys in Flinders R Surveys on Mitchell, estuary Flinders, Gilbert R estuaries Carpentaria Land Council Queensland Wader Study Group Aboriginal Corporation (CLCAC) Mar/April 2019, Dec 2019 Jan, April, Sept 2019, Apr 2020 (limited data) Mitchell Queensland Wader 1019 shorebirds (Mar2019) Study Group 7255 shorebirds (Dec 2019) March 2019 Dec 2019

Gilbert Flinders 5283 shorebirds (Mar 2019) 2244 shorebirds (Mar 2019) 3165 shorebirds (Incomplete, 851 shorebirds (incomplete, Dec Dec 2019) 2019) Gilbert & Mitchell R Low tide feeding sites

• Internationally significant (>1%) • Black-tailed Godwit • • Nationally significant (>0.1%) • Black Tailed Godwit • Red Neck Stint • Bar-Tailed Godwit • Greater Sandplover • Lesser Sandplover • Sharpe-tailed Sandpiper • Whimbrel • Eastern Curlew

Hansen et al. 2016 CLCAC – high tide Flinders counts

January 2019 15,090 March 2019 2513 September 2019 12,591 April 2020 1,130*

*COVID-19 restrictions Flinders R High tide roost sites

• Internationally significant • Great Knot • Red Knot • Black tailed Godwit • Bar Tailed Godwit • Curlew sandpiper • Eastern Curlew • Greater & Lesser Sand Plovers

Hansen et al. 2016 Bird counts over study - Flinders

16000 14000 12000 Large flood event 10000 8000 6000

Numbers of birds of Numbers 4000 2000 0 Jan Apr Sept Black tailed Godwit Great Knot Red Knot Total migratory birds

CLCAC data Flinders flood Feb/March 2019 Food for shorebirds How much mud- and sandflat habitat is in each estuary/nearshore area?

Mitchell River 7.5 km2

Gilbert River 7.5 km2

Flinders River 14.6 km2

Stephen Faggotter, Griffith U High abundance of benthic 16000 animals in Gulf rivers 14798

14000 2 12000

10016 10000 Mostly polychaetes

8000 7612

6000 5079

4000 Mean Individuals per m per Mean Individuals 1919 2000 1287 1363 1405 992

0 Bay of Rest, Roebuck Bay, Hinchinbrook Banc Haughton Gilbert River Flinders River Mitchell River CostaPunta WestOther WeststudiesChannel, (Aust, NE international)d'Arguin, estuary, NE Gilbertestuary Flindersestuary Mitchellestuary Morales, Australia Australia Australia Mauretania Australia CostaRica Rica Vikki Lowe, honours student Effect of freshwater flow

• Polychaetes • large species = long lived • Burrowing buffers low salinity • Densities do not change substantially after flooding • Longer billed birds can still access • Bivalves • Close valves, cease pumping • Densities change substantially after flooding • Favourite food of knots Nutrients stimulate algal growth on mudflats

250

200

/h)

/m 2 150

100 *** * **

Primary prod. prod. (mg Primary O 50

0 minus plus minus plus minus plus nutrients nutrients nutrients nutrients nutrients nutrients Flinders Gilbert Mitchell Floods bring nutrients & sediment which fuel productivity

Longer term Months - years

Short term Weeks - months Up to 3,500 tonnes nitrogen

Water, Nutrients & Sediment loads

Using ear bones to look at age and growth

1/3 mm thin section born 800 mm barra, 9 yrs old 1 2 3 4 4 yr old barramundi Distant between bands = annual growth

• Growth significantly & positively related 843 mm barra, 2 yrs old to flow, after accounting for age • Sequential pattern of river flow over multiple years is an important driver of barramundi population dynamics • Growth rates linked to flow. More extraction equals smaller fish J. Robins, Qld DAF

• What is the relative importance of each estuary for juvenile banana prawns?? How many prawns in each estuary in Nov 2016?

Mitchell 1.96 million Gilbert 0.64 million

Flinders 0.92/1.80 million

R. Kenyon, S. Faggotter How many prawns in each estuary in Nov 2017?

Mitchell 1.96 million Gilbert 0.75 million 0.64 million 1.55 million

Flinders 0.92/1.80 million 0.33/0.65 million Late dry season Wet season Post wet season Summary • Short term • Floods reduce food availability for birds

• Long term • Floods bring crucial nutrients to stimulate productivity • Flow is most critical in years of moderate to low flow • Flinders seems to be most productive & likely most vulnerable to development This work is supported through funding from the Australian Government’s National Environmental Science Program

For more information please contact: Name: Michele Burford Phone: 0429 199 755 Email: [email protected]