Biomass data for Snapper in South Australia

Having an understanding of how many fish are in the sea is fundamental for effective fisheries management. Scientists estimate the size of a fish stock, or its biomass, to assist fisheries managers determine how to sustainably manage the stock. View a timeline of past South Australian fisheries management decisions and the basis for those decisions.

Research methodology

SARDI scientists are able to estimate the biomass of Snapper’s spawning population through a combination of determining how many Snapper eggs are in the water, and what proportion of the adult population are spawning.

This method is known as the daily egg production method (DEPM) and has been used for a variety of other species like Sardines. The method effectively determines how many Snapper were required to spawn the measured density of eggs.

Confidently identifying Snapper eggs has been difficult in the past. SARDI scientists have overcome this by using a DNA marker to turn all Snapper eggs a blue colour, which makes them much easier to identify in mixed plankton samples.

Learn more about the daily egg production method (PDF 2.5 MB).

Snapper DEPM survey summary

  • The Snapper Egg Survey (daily egg production method) was conducted in Spencer Gulf from 4 to 15 December 2019. All 280 stations were successfully sampled. This survey included an extra 60 stations compared with the 2018 survey.
  • The Snapper Egg Survey (daily egg production method) was conducted in Gulf St. Vincent from 13 to 19 January 2020. 264 of the planned 272 stations were sampled. The omitted 8 stations were in areas too shallow to access, of these, 4 stations have never been sampled. The impact of omitting these stations is negligible. This survey included an extra 57 stations compared with the 2018 survey.
  • So far, SARDI has collected biological data from > 1,800 snapper sampled in 2019–20, including a comprehensive sampling program to collect adult snapper using commercial fishers in Spencer Gulf and Gulf St Vincent. Further sampling in collaboration with commercial MSF fishers is occurring in waters off the West Coast and South East.

View a map of the sample stations (PDF 617.2 KB).

Research shows Snapper in decline

The latest stock assessment (PDF 8.3 MB) reveals that the biomass of Snapper in South Australia’s Spencer Gulf/West Coast and Gulf St Vincent stocks have declined significantly. The results of the stock assessment modelling (which incorporates all DEPM survey estimates) show that:

Spencer Gulf/West Coast:

  • Biomass has declined by 91% from 5,350 t (±112) in 2005 to 468 t (± 72) in 2020.

Gulf St Vincent:

  • Biomass has declined by 90% from 4,355 t (±113) in 2011 to 457 t (± 81) in 2020.

Both stocks were determined to be recruitment impaired and subsequently classified as ‘Depleted’.

*All figures in brackets ( ) represent the standard error variance around the mean.

The weight of evidence from all scientific information available on Snapper shows consistent trends of decline.

More information

Page last reviewed: 25 Sep 2020

 


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