When do adult snapper arrive to Port Phillip Bay during each year's spawning migrations?
The earliest tagged snapper arrival occurred on September 2, 2012, but overall most fish arrived in October each year.
When do adult snapper leave Port Phillip Bay after each year's spawning season?
Two periods of snapper departures were discovered, the main period was December-January, and a smaller second period occurred in April-May.
How do these migration patterns relate to the bay's water temperature?
Most snapper arrived though Port Phillip Heads when the water temperature in the bay was between 13-16°C,
The peak period of detections on the main fishing grounds occurred in November, when the water temperature was between 16-18 °C,
The migrations are cued to ensure that the egg and larval stages develop in optimal temperature conditions of 18-22°C,
As temperature reaches 19°C adult snapper disperse away from the main Carrum Bight spawning region and many leave the bay, those that remain appear to go further south and likely stay deeper off Mornington.
Do 'individual' adult snapper come and go each year?
Yes, many snapper come and go each year and they show consistent times of arrival and departure (often within days between years - see the links to example movement maps)
Repeat migrants also generally used the same areas of the bay in different years.
How do they behave once in the bay?
During October-December adult snapper move around a lot. They rarely spend any more than one day near an individual listening station, and mostly spent less than a few hours at any one time,
Adult snapper commonly move distances of up 10 km in a 24 hour period, some fish traversed the bay from north to south in 24 hours, covering a distance of 40-50 km,
Adult snapper regular used artificial reefs, particularly in November, and repeatedly moved to and from specific locations, showing exceptional navigational capabilities.
What did the Pinkies do?
Pinkies showed much longer periods of residency at specific locations, often staying putt for weeks to months at a time,
Pinkies tagged on artificial reefs typically used these habitats over spring/summer but moved to natural reefs in the north of the bay (Mordialloc-Hobsons Bay) in autumn/winter,
Pinkies tagged on natural reefs almost exclusively used natural reefs,
Some Pinkies moved large distances from the Carrum Bight to Geelong Arm, typically following the shallow reef areas to the north and west,
Pinkies that were tagged on artificial reefs in summer and moved to naturel reef in autumn/winter often homed back to artificial reefs were they were tagged the following spring,
Only two pinkies appeared to leave the bay over the 400 day period of their tag life,
Overall pinkies showed a high dependency on shallow natural and artificial reef habitat.