In South Australia King George Whiting is the premium species in the multispecies Marine Scalefish Fishery, attracting the highest price per unit weight for commercial fishers. Assessment of the status of the South Australian stocks uses a weight-of-evidence approach that considers commercial catch-and-effort data, recreational fishery data, biological information on population size and age structures, and output from a computer fishery model that integrates these main input datasets. The primary indicators are hand-line effort and catch per unit effort (CPUE), and exploitation rate and biomass from the assessment model. The most recent assessment was completed in July 20142.
Gulf St Vincent (South Australia) biological stock
The Gulf St Vincent biological stock is found throughout Gulf St Vincent and Investigator Strait, and around Kangaroo Island. Hand-line effort for this stock has declined since 2009, and hand-line CPUE has declined since 20072. Both of these declining trends for this species are consistent with a declining level of biomass, since, given the value of the species, it is expected that effort would remain high or consistent if biomass were available. The model-estimated biomass for this stock has been relatively flat for recent years. However, because the estimates of effort and CPUE used in the model did not take into account a likely increase in the ‘effective’ effort, and because of uncertainty in the time series of recreational catch and effort, the decline in fishable biomass is likely to have been greater than suggested by the model output. Although it is likely that the biomass of King George Whiting has declined between 2009 and 2013, the stock is not yet considered to be in a recruitment overfished state. However, the above evidence indicates that the current level of fishing pressure is likely to cause the stock to become recruitment overfished.
On the basis of the evidence provided above, the biological stock is classified as a transitional– depleting stock.
Spencer Gulf (South Australia) biological stock
The Spencer Gulf (South Australia) biological stock extends throughout the entire northern and southern regions of Spencer Gulf. Both catch and effort for this region have shown recent declining trends, culminating in the lowest recorded values for both in 20132. Furthermore, CPUE has declined for this region since 2007. As discussed above for the Gulf St Vincent stock, such trends in fishery statistics for this high-value species are consistent with a declining biomass. This is reflected in the model outputs, which indicate that there was a marginal decline in biomass between 2008 and 2013. Because the estimates of effort and CPUE used in the model did not take into account likely increases in ‘effective’ effort, and because of uncertainty in the time series of recreational catch and effort, the decline in fishable biomass may have been greater than suggested by the model output. Although declining slowly, the stock is not yet considered to be in a recruitment overfished state. However, the above evidence indicates that the current level of fishing pressure is likely to cause the stock to become recruitment overfished.
On the basis of the evidence provided above, the biological stock is classified as a transitional– depleting stock.
West coast—Eyre Peninsula (South Australia) biological stock
This biological stock extends throughout all the bays and offshore areas of the west coast of the Eyre Peninsula. Hand-line fishing effort for this stock was relatively stable in recent years. Catch increased for a number of years, and hand-line CPUE increased until 2013, reaching the highest level ever recorded2. Output from the stock assessment model showed trends of increasing recruitment rates and levels of biomass between 2004 and 2013. Furthermore, between 1984 and 2013, the exploitation rate fell considerably, relating to long-term declines in commercial and recreational fishing effort. The above evidence indicates that the biomass of this stock is unlikely to be recruitment overfished and that the current level of fishing mortality is unlikely to cause the biomass to become recruitment overfished.
On the basis of the evidence provided above, the biological stock is classified as a sustainable stock.
Western Australia
The life cycle of King George Whiting in Western Australia involves both inshore and offshore habitats; juvenile fish occupy near-shore waters in estuaries and protected coastal embayments before migrating to deeper waters as they mature (at around 40 cm), where they remain. Because of this offshore, size-related movement, it is difficult to obtain a representative sample of the age structure for the overall population to reliably estimate fishing mortality using traditional methods. A novel modelling approach was thus developed to produce estimates of fishing mortality that account for the offshore movement of this species4. These estimates were subsequently applied in a per-recruit analysis.
The status of the King George Whiting stock in Western Australia was recently assessed in 2013 using a weight-of-evidence approach that included estimates of fishing mortality and per-recruit analyses determined in the modelling approach, as well as commercial and recreational catch and catch rates, and fishery-independent juvenile recruitment indices5. Using age data collected during 2010 to 2012, fishing mortality for the King George Whiting breeding stock (offshore component) was estimated to be low (below the target fishing mortality [Ftarget]). At current estimated levels of fishing mortality for King George Whiting, the spawning potential ratio (based on the spawning biomass per recruit) was estimated to be at a sustainable level (42 per cent). Catch and catch-rate trends for the main commercial fisheries in Western Australia (South Coast Estuarine Managed Fishery and West Coast Estuarine [Interim] Managed Fishery) are confounded by environmental influences in these estuarine systems (for example, sandbar closing and opening). They are, however, within the historical range and are considered acceptable, as the data indicate no evidence of a declining stock biomass. Trends in recreational catch and catch rate are difficult to interpret because of the infrequent nature of the surveys, different designs of the surveys, and changes to size and bag limits. Annual trends in recruitment appear to correlate with trends in the recreational catch, with a time lag of 2–3 years. Annual recruitment by juvenile (age zero years) King George Whiting has been highly variable since recruitment surveys began in 1999. Recruitment levels were relatively high in 1999, 2000 and 2008 but were at more typical low levels in most other years. The high recruitment levels were observed during strong Leeuwin Current (La Niña) years. The above evidence indicates that the biomass of this stock is unlikely to be recruitment overfished.
The King George Whiting stock is exposed to relatively high fishing pressure on the inshore component of the stock, which is entirely comprised of immature fish. However, the breeding stock is offered some protection by its unidirectional offshore migration to deeper waters, where individuals tend to become more dispersed and less easily targeted. The current level of fishing mortality is unlikely to cause the stock to become recruitment overfished.
On the basis of the evidence provided above, King George Whiting in Western Australia is classified as a sustainable stock.
Victoria
Stock status assessment of King George Whiting in Victoria uses a weight-of-evidence approach that considers CPUE from both the commercial and recreational sectors, fishery-independent annual surveys of pre-recruit (post-larval) catch rates in Port Phillip Bay, and age–length composition of the catch. Importantly, the indicator data are derived from bay and estuary fisheries that only target juvenile King George Whiting.
When describing the status of the Victorian King George Whiting stock, it is important to consider how life history characteristics influence the above indicators. The dynamics of King George Whiting populations and fisheries in Victorian bays and estuaries are strongly influenced by climatic factors that influence the numbers of larvae transported into the bay and estuary nursery grounds during spring each year6–8. Because King George Whiting leave these nursery areas permanently by 4–5 years of age (before adulthood), the fisheries in bays and estuaries are based on only a few age classes at any point in time (typically 2–4-year-olds)7,9. This means that the fisheries are highly variable in response to the variable supply of these larval stages. Over the past 60 years, King George Whiting fisheries production in Victoria’s bays and estuaries has shown peaks and troughs at approximately 10‑year intervals7,9.
The most recent formal stock assessment of Victorian King George Whiting was in 201010. Review of more recent commercial fisheries data (Port Phillip Bay Fishery and Corner Inlet Fishery) indicates that the King George Whiting fishery productivity and biomass (that is, catches and CPUE) have declined since the previous peak in 2011. This decline is within historical variability and is consistent with the low numbers of post-larvae observed by fishery-independent pre-recruit surveys from 2009 to 2012 in Port Phillip Bay. However, the pre-recruit survey in spring 2013 showed a major increase in the abundance of post-larvae recruiting in Port Phillip Bay. Therefore, while fishery production and biomass in Port Phillip Bay will continue to be lower than average, and will likely decline further in 2014–15, they are expected to increase significantly in 2015–16. The situation for the Corner Inlet Fishery is less certain, as pre-recruit surveys are not conducted for this location. Effort for all gear types in Victoria has decreased since 1999, as a result of the reduction in the number of licensed fishers in Victorian waters, and is at historically low levels. Further, consistent with the lower catches of King George Whiting in the Port Phillip Bay Fishery and Corner Inlet Fishery in recent years, effort with the main gear type, haul seines, has decreased.
The decline of catches and CPUE in recent years is consistent with environmental influences reducing larval supply to bays and estuaries in the previous 3–5 years. The recent poor post-larval recruitment of King George Whiting into the bay and inlet nursery areas, combined with fishing mortality and the natural movement of older King George Whiting to coastal waters, has led to the notable recent decline in catches and catch rates in the key fishery areas. However, the King George Whiting stock is exposed to relatively low fishing pressure in the offshore waters where the adults reside. The available information, along with consideration of the species’ life history, indicates that, although biomass has declined in the major bay and inlet fisheries, the biomass of the stock is unlikely to be recruitment overfished. The current level of fishing pressure is also unlikely to cause the stock to become recruitment overfished.
On the basis of the evidence above, King George Whiting in Victoria is classified as a sustainable stock.