Victoria’s Game Management Authority has provided the December 2017 paper on the blue-winged shoveler and it makes for very interesting reading.
As the report summary notes, the Australasian shoveler is a game species in Victoria and has been subject to recreational hunting for more than 150 years. The species hasn’t been hunted in recent years and the paper provides the background for this decision.
So, what do we learn from the report?
That “ …recent aerial monitoring data (1983–2016) shows a decline in population abundance of shoveler, raising questions about its suitability as a game species.”
This observation is in the context that “Dispersal movements are poorly understood in Australia …”
We read that shoveler breed on the ground and are susceptible to predation, being trampled by livestock or destroyed by other agricultural activities. They are considered one of the least common duck species in south-eastern Australia and were listed as Vulnerable in Victoria in 2012, with the main recognised threats being habitat degradation and introduced predators.
In 1988, a harvest limit of two Australasian shoveler per day per hunter was imposed and this continued until 1999 (except for 1998 when the limit was one bird per hunter per day). The limit has remained at one or two Australasian shoveler per day since then, except for the years 2004, 2009, 2016 and 2017 during which it was excluded from hunting.
In assessing its continued suitability as a game species, three sources of monitoring data were used: the Eastern Australian Aerial Waterbird Count (EAAWC), waterfowl abundance (ground counts) and wetland condition surveys in South Australia and waterbird monitoring (ground counts) at the Victorian Western Treatment Plant.
The southern oscillation index (SOI) and the standardised precipitation evapotranspiration index (SPEI) were used as potential predictors of wetland availability to model population trends.
According to the report: “This analysis demonstrated that shovelers exhibited a general declining trend, which did not respond strongly to changes in either SOI or SPEI. Recent increases were noted for the counts in South Australia but it was not possible to discriminate whether populations were recovering in that region as opposed to congregating in more resilient wetland areas.”
A simpler model (with no environmental variables) was used to predict the expected EAAWC population size for the subsequent 10 years and probability of it dropping below a critical threshold at different harvest rates.
The estimates of probabilities of quasi-extinction were larger than 25 per cent in the first year, even with no harvest. These declined to 11.8 per cent in 2026 when no harvest was assumed, while staying approximately stable (~26.8 per cent) with a 10 per cent harvest, and rapidly increasing to > 50 per cent in only four years with a 30 per cent harvest.
Ultimately this led to the following recommendation: “Based on life history characteristics, current and likely future population trends and predicted influence of harvest on population growth rates, it is recommended that the Australasian shoveler be exempt from recreational harvest in Victoria for the foreseeable future.”
The prospect of a review sometime in the future if population data improves is little comfort for hunters.
The report confirms that EAAWC produces limited data for Victoria and is problematic, and a further recommendation underlines the need to build better scientific knowledge, including tracking and counting.
The report also notes, as hunters well understand, that habitat has the greatest influence on populations, as well as predation.
Hunters play an active role in conservation and predator management and they can play a significant role in new science, including monitoring and counting of shoveler.
However, effectively removing a game species is hardly motivation and could end up being counterproductive, especially when the modelling clearly indicated that some hunting of shoveler could have been be maintained.