The mystery of the disappearing Flathead
Sand Flathead (Platycephalus bassensis) were one of the most commonly caught fish in the Bay. But since the 1950′s, their Bay population is believed to have declined more than 90%, cause unknown. SF’s were most abundant in the Bay on the muddy bottom of central basin, where they wait, partly buried in the soft seabed, to ambush prey including small fish, crustaceans, worms and molluscs.
Spot the fish....
Fish habitats in the Bay can be affected by physical changes to the seabed due to dredging and sedimentation; chemical changes such as introduction of industrial contaminants; and biological processes such as increased population and movements of other species.
Dumping of contaminated sediments dredged from the Yarra has been ongoing since a major river widening project in the 1940-s and 50′s. This dredge disposal site, around 20km south of Williamstown, is likely to have changed the physical and chemical nature of the central basin.
Even before the recent Channel Deepening Project, contaminants such as DDT, PCB, and others, were known to have dispersed from this site. But there seems to have been no thorough investigation of possible links between Sand Flathead decline and dredge spoil dumping. If such studies are underway, Baykeeper would love to hear about them!
The North Pacific Seastar and fishing are the only factors mentioned as possibly explaining the decline in: http://www.fishingmonthly.com.au/Articles/Display/1446-Port-Phillip-Bay-sand-flathead-stock-assessment
That doesn’t rule out habitat and environment but we need a stronger continuing science commitment to the Bay to keep it healthy, especially as climate change impacts are increasing.
North Pacific Seastars arrived in the Bay about 40 years after the Flathead decline began. It’s worth noting that the sand flathead Stock Assessment Workshop at Primary industry Research Victoria’s (PIRVic) Queenscliff marine science facility didn’t consider the possible environmental impacts of dredge spoil on Sand Flathead habitat.
It sounds like we should be asking the government to undertake the necessary study. Who should we write to?
Spot on Fran. The Minister currently responsible for fisheries is Joe Helper. His Department of Primary Industries includes the Marine and Freshwater Research Institute. MAFRI would be the logical people to conduct the research if funding was made available. I understand that a portion of the money received from fishing licence fees is allocated to such projects.
If money was available the key thing would be to design the study to ensure clear conclusions can be drawn. Comparison of population trends outside the bay would be useful. But the best place to start would be to review all previous studies of toxicity in fish in the central Bay area, and design a study to answer any unresolved issues. For example, Langdon (1986) found chronic haemosiderosis in the internal organs of Sand Flathead. Lead and several other pollutants were considered the most likely cause.
An interesting announcement from the current round of the Recreational Fishing Grants Program (sourced from recreational fishing license revenue) is as follows:
“$300,000 to conduct research into improving sustainability of sand flathead stocks by assessing whether or not fishing activity is having any impact on the decline of sand flathead numbers or if the decline is due to other reasons not related to fishing”.
Thanks for letting us know Ben. This research is definitely a step in the right direction, provided the study looks closely at all possible causes of flathead decline. If it just examines whether over-fishing is the problem, at the end of the study we may still not know what the cause is. Has the scope of the study been set?