Sand flathead science

World-class research underpins our understanding of what is happening to Tasmania’s sand flathead fishery, and it will also be our guide to recovering stocks for a better flathead future.

There are multiple flathead research projects currently underway or planned that are improving our understanding of the sand flathead fishery. The Institute for Marine and Antarctic Studies (IMAS) was recently awarded a $3.3 million grant to research sand flathead recovery.

Sand flathead stock assessment

Every year, IMAS conducts stock assessments for key scalefish species in Tasmania. These stock assessments tells us whether current management is suitable for a fishery to continue to be sustainable, or whether management changes are needed.

In the most recent 2021/22 stock assessment, sand flathead was classified as ‘depleted’. This is the most serious classification for a fishery.

STOCK STATUS
DEPLETED
​ ​Recreational catches dominate landings of southern sand flathead in Tasmania. Fishery independent surveys suggest low abundances of legal sized fish in southeast and eastern Tasmania where populations are subject to heavy fishing pressure. While undersized fish appear to be abundant, newly introduced length-based assessment approaches indicate that female stock biomass is likely to be depleted in most regions. Moreover, current levels of fishing pressure are unlikely to be sustainable, specifically where stock rebuilding is likely to be most urgently needed.


Findings from the most recent stock assessment informed recent changes to sand flathead rules through the Scalefish Rules Review.

The key findings of the most recent stock assessment were that:

  • Numbers of flathead larger than 32 cm are low.
  • The average size of a flathead is getting smaller.
  • Most flathead are caught within a year of reaching legal size in heavily fished areas.
  • Large breeding females are depleted in most areas.
  • Fishing is removing faster-growing fish, leaving more genetically stunted flathead to breed.

In the southeast, biomass of flathead is less than 17% of what it would be if no fishing occurred, and fishing pressure is up to 4x to high.

 Scientific Advice on Sand Flathead Management Scenarios from IMAS

 Sand Flathead What's Happening in the Fishery


How have sand flathead become depleted?

Patterns in the numbers and size of sand flathead show that high fishing pressure has caused sand flathead stock depletion. High fishing pressure has had two main impacts on the stock: biomass depletion and genetic stunting.

Biomass depletion

Both fishers and scientists have observed that sand flathead larger than 32 cm are getting harder to catch, as most fish are quickly caught and kept once they reach 32 cm. This has had a large impact on the overall biomass of sand flathead, especially large breeding females.


Watch the video below for more information.

 


Genetic stunting

Scientists and fishers have noticed that the average size of sand flathead is getting smaller. While this is partly due to the biomass depletion of large fish, it is also from genetic stunting as a result of high fishing pressure.

Large, fast-growing fish reach the legal size sooner than their small, slow growing counterparts. This means that fast-growing fish are caught sooner and survive fewer spawning seasons to contribute to the next generation of sand flathead. The result is small, slow growing fish become increasingly common.

Watch the video below for more information.

 


How does the stock assessment work?

Most fisheries stock assessments are based on commercial catch reporting data. However, because so little sand flathead is caught by commercial fishers, IMAS does independent sampling to assess sand flathead stocks.

They do this by fishing for sand flathead in popular fishing areas around the state. From the fish they catch, they collect data like fishing effort, age, growth and fishing mortality. The places, times and methods used each year when fishing are the same to help scientists identify changes in the fish stock over time. 

If researchers changed their methodology each year (e.g. by shifting where or when they fish or using different gear) it would be difficult to know whether changes in catch were because something had changed in the fish stock, or because of the new methods being used.

Recreational Fishing Survey

Every five years, IMAS conducts a telephone survey of recreational fishing in Tasmania. They estimate information about recreational fishing statewide, including recreational catch of different species.

From this survey, we know that sand flathead is the most popular recreationally caught species, with an estimated 184 tonnes caught in 2018. Seventy percent of recreational scalefish catch is sand flathead.

IMAS conducted the most recent survey between November 2022 and October 2023, and the results, including updated information about recreational sand flathead catch, will be available in 2024.

Read more about the Recreational Fishing Survey.


    Contact

    Recreational Fishing Enquiries
    Level 3, 134 Macquarie St
    Hobart TAS 7000
    Phone: 03 6165 3233, 1300 720 647
    Email: fishing.enquiries@nre.tas.gov.au

    Hotline

    Fishwatch Report illegal fishing

    0427 655 557

    What to report? arrow button

    Contact us

    Recreational Fishing

    Level 3, 134 Macquarie St

    Hobart TAS 7000

    Phone: (03) 6165 3233, 1300 720 647

    Email: fishing.enquiries@nre.tas.gov.au

    Commercial Fisheries

    Level 3, 134 Macquarie St

    GPO Box 44

    Phone: (03) 6165 3000, 1300 368 550

    Email: commercial.fisheries@nre.tas.gov.au

    Commercial Fisheries Licensing

    Level 1, 134 Macquarie St

    GPO Box 44

    Phone: (03) 6165 3000, 1300 368 550

    Email: fishing.licensing@nre.tas.gov.au