Tracking the habitat preferences, spawning locations and movements of Dusky Flathead in the Gippsland Lakes

A large research project to investigate the movement patterns of Dusky Flathead throughout Australia’s largest estuary; the Gippsland Lakes, was funded by the Recreational Fishing Licence Trust. This project was run through a partnership between the Nicholson Angling Club and Dr Jeremy Hindell, Department of Sustainability and Environment.

Acoustic telemetry was used to document patterns of movement by dusky flathead throughout the Gippsland Lakes. Forty fish were surgically implanted with acoustic transmitters and monitored over 18 months (December 2006 to June 2008).

Overall, many of the fish were largely sedentary, and remained in single regions of the Gippsland Lakes for extended periods (up to several months). This was particularly evident for fish tagged in the lower Lakes region, between Metung and Lakes Entrance. Fish appeared to spend most of their time in the Lakes, however, fish often moved into the lower and middle reaches of major tributaries such as the Tambo, Mitchell and Nicholson Rivers, and appeared to ‘reside’ in these regions for periods of up to several weeks.

Larger movements up to 30 km over two to three days were shown, but were not common. One fish moved from McLennan Strait to Lakes Entrance in December 2007, but did not leave the Lakes.

During the large flood of June 2007, fish moved in subtle ways, with several fish moving to more saline regions of the Lakes closer to the entrance (e.g. Lakes Entrance), however, no fish were recorded to exit the Gippsland Lakes during this flood.

Most tagged Dusky Flathead were detected infrequently on the array of acoustic receivers set up throughout the Gippsland Lakes. The array used for this study was an existing array established to monitor movement patterns of Black Bream, with most bream being recorded daily. Due to the much lower number of detections it was not possible to separate the extent to which Dusky Flathead were truly sedentary (i.e. remained in a single location for extended periods of time) versus highly mobile but limited in their movements (i.e. frequent excursions over scales of 100s of ms to kms).

Table 1. Summary of catch details and movements by dusky flathead throughout the Gippsland Lakes. Details shown only for those fish that were detected.

Date of release	Total Length (mm)	Weight (g)	Location of release	ExternalTag #	Summary of movements
17/01/2007	480	722	Potty Point	4823	Only detected in bottom lake around point of release.
17/01/2007	460	555	Potty Point	4820	Detected around point of release until December 2007. Then swam towards entrance via main channel. Detected at entrance for several days at end of December 2007, then swam back to original point of release via bottom channel.
17/01/2007	495	700	Potty point	4819	Only detected around point of release.
17/01/2007	435	534	Rigby Island	4818	Only detected around point of release.
17/01/2007	680	2102	Potty Point	4821	Detected around Potty Point until 4/6/2007. Moved to Lakes Entrance by 13/6/2007. Moved back to Reeve channel on 13/6/2007, and detected here until 16/8/2007. Moved back to Potty Point by 28/8/2007. Detected here until 16/3/2007.
17/01/2007	530	943	Potty Point	4822	Detected around Potty Point until 3/6/2007. Moved to Lakes Entrance and not detected again after 4/6/2007. Possibly moved out of the Gippsland Lakes.
16/03/2007	440	548	Mitchell River cut	4860	Stayed around the entrance to the Mitchell River, where it was last detected 18/5/2007.
8/04/2007	440	530	Nicholson river	4880	Stayed around the middle reaches of the Nicholson River until 11/5/2007. Then moved to the Nicholson River Entrance by 11/5/2007. Stayed in this vicinity until 13/5/2007, then returned to middle of Nicholson River by 15/5/2007. Returned to the Nicholson River entrance on 20/5/2007. Then returned to middle of Nicholson by 22/5/2007. Last detected outside Nicholson River on 22/5/2007.
2/05/2007	375	340	Hollands Landing	4900	Moved from McLennan Strait to sperm whale head between 23/9/2007 and 15/12/2007. Stayed around Sperm whale head until 23/12/2007. Then moved to Metung by 27/1/2007.
2/05/2007	440	570	Hollands Landing	4898	Only detected around McLennan Strait east.
2/05/2007	430	560	Hollands Landing	4893	Moved from the eastern end of McLennan Strait to the western end between 25/5/07 and 28/6/07. Detected around the western end of McLennan Strait until 1/12/2007. Then moved to Sperm Whale Head by 9/12/2007. Then moved to Rotamah Island on same day. Then moved to Paynesville by 14/12/2007. Then moved to Metung by 17/12/2007. Then moved to Lakes Entrance by 19/12/2007. Then moved back to Metung by 22/12/2007. Then moved back to Raymond Island by 5/1/2007. Then back to Metung and on to lakes Entrance by 4/2/2007.
2/05/2007	430	520	Hollands Landing	4895	Detected around the eastern end of McLennan Straits until 15/6/2007. Then moved to Bunga Arm by 13/12/2007. Then to Paynesville by 16/1/2008, and then to Reeve Channel by 29/1/2008.
2/05/2007	430	520	Hollands Landing	4894	Only detected around the eastern end of McLennan Straits.
2/05/2007	480	650	Hollands Landing	4899	Stayed around the eastern end of McLennan Straits for the entire period. Last detected in this area on 9/6/2008.
2/05/2007	480	640	Hollands Landing	4897	Stayed around release location until 24/6/2007. Then swam rapidly to Sperm Whale Head by 17/7/2007. Returned to release location by 24/7/2007.
6/12/2006	350	285	Mitchell river boat ramp	4831	Stayed around Mitchell River cut until 13/12/2006. Then swam to Mitchell River entrance by 17/12/2006. Stayed around the entrance until 26/12/2006. Then swam back to the Mitchell River cut by 27/12/2007. Stayed around the cut until 1/1/2007, then swam back to Mitchell River entrance by 2/1/2007. Stayed around The Mitchell River entrance until 9/1/2007, then swam to Paynesville by 22/1/2007. Stayed around Paynesville until 23/1/2007, then swam back to Mitchell River entrance by 23/2/2007. Stayed around Mitchell River entrance until 9/3/2007, then swam back to the cut by 9/3/32007. Last detected at the Mitchell River cut on 14/3/2007.
18/12/2006	470	730	Tambo river entrance	4855	Stayed around release location until 26/3/2007.
18/12/2006	435		Tambo river entrance	4858	Stayed around release location until 13/2/2007.
18/12/2006	440	480	Tambo river entrance	4856	Stayed around release location until 25/2/2007.
18/12/2006	435	450	Tambo river entrance	4852	This fish moved upstream into the Tambo River, where it was re-caught around Johnsonville. The angler kept the fish but returned the electronic tag. We re-used this tag, inserting it in a fish captured during a Nicholson Angling Club Easter Competition (see Fish 4880, above).
18/12/2006	335	320	Tambo river entrance	4851	This fish spent most time around the Tambo River entrance. Made a few brief movements to the middle of Tambo River. Not detected again after leaving the Tambo river entrance on 21/4/2007.
18/12/2006	380	350	Tambo river entrance	4853	Stayed around Tambo River entrance until 21/1/2007. Then swam to Metung by 30/1/2007. Stayed around Metung until 9/5/2007, then returned to Tambo River entrance on 14/5/2007. Moved to middle of Tambo River, then returned to Tambo River entrance. Departed Tambo River entrance on 21/5/2007, swam to Mitchell River entrance by 30/5/2007, and then moved to Metung by 9/6/2007. Last detected in the Metung area on 20/10/2007.
18/12/2006	415	450	Tambo river entrance	4854	Moved from Tambo River entrance to Mitchell River entrance on 1/2/2007, and not detected since.
18/12/2006	420	505	Tambo river entrance	4857	Only detected around Mitchell River entrance, where this fish stayed for several months up until 12/7/2007.

Recreational Fishing Grant Program - Research Report - Gippsland Lakes dusky flathead tracking project: R/05/06/01

This is the first study to evaluate the movements of dusky flathead using acoustic telemetry. The generally limited movement of fish throughout this study suggests that a more spatially focussed program, undertaken at a scale of kms rather than 10s of kms, is required to better understand details on specific habitat affinities and identify likely spawning locations. Acoustic telemetry is suitable, however, in demonstrating how far and when fish move, and the results of this study provide valuable information that can be used in assessing population structure and broad-scale affinities for this species.

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