The Victorian Fisheries Authority revealed the mysteries of Port Phillip Bay’s pink snapper migration by using acoustic tags implanted in fish.
From November 2011, tags were surgically inserted in fish.
Acoustic tags emit acoustic signals that can be detected by listening stations, which were installed throughout the bay.
The listening stations could detect tagged fish from 300m to 400m away.
The tagging system allowed fisheries staff to log data on dates, time and unique ID of each fish.
This allowed mapping of each snapper’s movements, giving fishermen unprecedented new information on overall snapper migrations through the year.
By December 2013 about 150 snapper from 22cm to 87cm in length had been tagged in Port Phillip Bay.
The movements of the fish were monitored until January 2015.
The results showed snapper had an annual migration into and out of the bay that was subject to water temperature.
Adults schooled in November in the Carrum Bight to Hobsons Bay region near the Yarra River outflow, loitering in a large eddy.
This eddy held the snapper eggs and larvae in a good feeding environment.
Adult and juvenile snapper showed navigation talent, being able to repeatedly find artificial reefs, and could find their way in and out of the bay, arriving only days apart each year.
The earliest tagged snapper arrivals were on September 2, but most fish arrived in October each year.
Two periods of snapper departures were discovered, the main one being December-January, and a smaller one from April-May.
Most snapper arrived though Port Phillip Heads when the water was between 13-16C.
Peak detections on fishing grounds were in November, when the water temperature were between 16-18C.
As temperatures reached 19C adult snapper moved away from the Carrum Bight spawning region and many left the bay, those that stayed went south and likely stayed in deep water off Mornington.
During October-December the adult snapper were seen to move around, rarely spending any more than a day near a tag listening station.
Adult snapper commonly moved up to 10km in 24 hours, some fish moved across the bay from north to south in 24 hours, covering 50km.
Adult snapper used artificial reefs, particularly in November, and often moved to and from specific locations, showing navigational skill.
Small snapper (pinkies) stayed longer at locations, often for months at a time.
Pinkies on artificial reefs 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 long distances from Carrum Bight to Geelong Arm, following shallow reef to the north and west.
Only two pinkies left the bay over the 400 days of their tag life.
Pinkies showed dependency on shallow reef habitat.
The information proved to be invaluable for fishos, who now know when the best times are to target the bay’s snapper.
Snapper respond well to most fresh baits presented on paternoster rigs.
The turn of the tide is a fine to catch them, with high tide best on shallow reefs, and night fishing works well in busy areas.
The bay’s artificial reefs were clearly a good spot to target these fish, and given how mobile they are, yesterday’s dud spot could be firing today, and visa versa.
Here is a list of recommended tackle for Victorian waters.