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 shows Snapper in decline
The latest stock assessment () reveals that the biomass of Snapper in South Australia’s Spencer Gulf and Gulf St Vincent has declined significantly since the last equivalent study in 2013-14.
Spencer Gulf between 2013-14 and 2018:
- Northern Spencer Gulf biomass declined by 15.7 per cent, from 127 (+/- 53)* tonnes to 107 (+/- 58) tonnes.
- Southern Spencer Gulf biomass declined by 30.3 per cent, from 122 (+/- 40) tonnes to 85 (+/- 25) tonnes.
- Total Spencer Gulf biomass declined by 22.9 per cent, from 249 (+/- 67) tonnes to 192 (+/- 63) tonnes.
Gulf St Vincent between 2013-14 and 2018:
- Northern Gulf St Vincent biomass declined by 85.3 per cent, from 1,890 (+/- 1,039) tonnes to 277 (+/- 125) tonnes.
- Southern Gulf St Vincent biomass declined by 90.6 per cent, from 700 (+/- 322) tonnes to 66 (+/- 33) tonnes.
- Total Gulf St Vincent biomass declined by 86.8 per cent, from 2,590 (+/- 1,088) tonnes to 343 (+/- 130) tonnes.
*All figures in brackets ( ) represent the standard error variance around the mean.
Note that Spencer Gulf survey area was the northern end of the Gulf; data above reflects northern and southern data sets within that area.
The weight of evidence from all scientific information available on Snapper shows consistent trends of decline.
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.