Australian Sardine Sardinops sagax

The maximum sustainable yield for species at a low trophic levels (forage species), such as Australian Sardine, is typically achieved at a depletion level of approximately 60 per cent, equivalent to 40 per cent of unfished biomass⁵. However, harvest strategies for fisheries for these species also need to consider potential impacts on biodiversity, and ecosystem structure and function^6,7. Biomasses above 75 per cent of the unfished level have been identified as a global average for achieving a balance between protecting ecosystem function and biodiversity, and providing for food production and economic development of low–trophic level species⁵. However, the south-east Australian ecosystem, including the Great Australian Bight, has been shown to be less sensitive to harvesting of low–trophic level species than other systems worldwide⁵. A recent study using ecosystem models suggests that maintaining biomasses of small pelagic fishes above 50 per cent of the unfished level will maintain the biodiversity and health of Australia’s marine ecosystems⁸. Management strategy evaluations suggest that exploitation rates of less than about 30 per cent maintain the spawning biomass of Australian Sardine above 50 per cent of the unfished level⁸.

Low–trophic level species often undergo large fluctuations in abundance over a variety of spatial and temporal scales. For example, two mass mortality events in the 1990s, caused by Herpesvirus, each killed up to 70 per cent of the adult population of Australian Sardine^1,9,10. As well, considerable time and resources are required to develop robust estimates of biomass, and undertake the population modelling required to obtain the estimates of current and virgin biomass that are needed to estimate levels of depletion. For these reasons, performance indicators that relate to levels of depletion of unfished biomass have not been established for Commonwealth and state fisheries for Australian Sardine during their developmental phases ^11,12. Instead, exploitation rates (that is, catch as a proportion of spawning biomass), based on estimates of spawning biomass obtained using the daily egg production method (DEPM)^13–15, have been used as performance indicators for setting total allowable commercial catches. More recently in the South Australian Sardine Fishery, estimates of spawning biomass have also been used as target and limit reference points. However, in the absence of reliable estimates of virgin biomass, it is difficult to relate these indicators to levels of depletion. Ecological performance indicators monitored and modelled in relation to the South Australian Sardine Fishery, combined with recent analyses⁸, suggest that exploitation rates of up to 30 per cent are likely to maintain spawning biomass at levels that take into account the ecological importance of Australian Sardine ^5,6,11,12.

The information available to assess stock status and the frequency of formal assessments vary among jurisdictions, largely in response to recent catch levels. Catch-and-effort data are monitored annually in all jurisdictions; estimates of spawning biomass have been obtained using the DEPM for each of the four biological stocks; and population modelling has been undertaken for the southern Australian biological stock and the two western Australian biological stocks.

Eastern Australian biological stock

Estimates obtained in 1997, 1998 and 2004 using the DEPM suggest that the spawning biomass of Australian Sardine off eastern Australia is at least 25 000–30 000 tonnes (t)^16–18. Catches reached almost 5000 t in 2008–09, but declined to 1097 t in 2012–13 as a result of a reduction in fishing effort; this was partly caused by the destruction of a processing plant in Eden, New South Wales¹⁶. Catches from a vessel operating out of Lakes Entrance in Victoria have increased in recent years. The highest annual catch (approximately 5 t in 2009) was around 17 per cent of the best estimate of spawning biomass (around 29 000 t, based on samples collected in 2004). Recent catches equate to exploitation rates of less than 10 per cent¹⁶. The current level of fishing mortality is unlikely to cause the stock to become recruitment overfished¹⁹.

On the basis of the evidence provided above, the biological stock is classified as a sustainable stock.

Southern Australian biological stock

The majority of the catch from the southern Australian stock is taken from South Australia, with much smaller catches from Port Phillip Bay, Victoria. Assessment of the South Australian Sardine Fishery has involved annual and, more recently, biennial DEPM surveys, and population modelling based on spawning biomass estimates, catch and catch-at-age data^20,21. The most recent estimate of spawning biomass was around 150 000 t²⁰, which is above the limit reference point of 75 000 t identified in the management plan²¹. The stock is not considered to be recruitment overfished. The current exploitation rate is around 23 per cent (that is, 34 000 t from an estimated spawning biomass of approximately 150 000 t), which is below the upper target reference point of 30 per cent. This exploitation rate is unlikely to cause the stock to become recruitment overfished.

On the basis of the evidence provided above, the biological stock is classified as a sustainable stock.

Western Australia west coast biological stock

Population modelling, based on spawning biomass estimates (estimated using the DEPM), and catch-at-age and catch data²², suggest that exploitation rates since the late 2000s for the Western Australia west coast stock are less than 10 per cent (2328 t from an estimated spawning biomass of approximately 25 000 t)²³. The stock is not considered to be recruitment overfished. This level of fishing mortality is below the limit reference point and is unlikely to cause the stock to become recruitment overfished.

On the basis of the evidence provided above, the biological stock is classified as a sustainable stock.

Western Australia south coast biological stock

Population modelling, based on spawning biomass estimates (estimated using the DEPM), and catch-at-age and catch data²³, suggest that exploitation rates since the late 2000s for the Western Australia south coast stock are around 3 per cent (less than 3000 t from an estimated spawning biomass of approximately 97 000 t)²³. The stock is not considered to be recruitment overfished. This level of fishing mortality is below the limit reference point and is unlikely to cause the stock to become recruitment overfished.

On the basis of the evidence provided above, the biological stock is classified as a sustainable stock.