Why has the Change been Made?
In 1998, Victoria's Hunting Advisory Committee was advised by the then Minister for Conservation and Land Management that a decision had been taken by the Victorian State Government to implement the recommendations of a recent investigation into the continued use of lead shot in Australia. The investigation was undertaken by the Australian and New Zealand Environment and Conservation Council (ANZECC).
The thrust of the ANZECC report was that, based on widespread studies both overseas and in Australia, the level of poisoning occurring in some waterfowl species, across a range of habitats, had reached levels where the use of lead shot for waterfowl hunting should be progressively phased out.
The HAC offered its services to liaise with the Department and hunting organisations, to ensure that hunters, as the people most affected by the decision, have an active role in ensuring a sympathetic implementation process. The project was developed by a sub-committee of experienced members from Field and Game Australia, Shooting Sports Council of Victoria and the Sporting Shooters Association of Australia.
The Lead Poisoning Problem
Some waterfowl species eat natural grit as an aid to digestion of food and may mistakenly collect spent lead pellets instead. These pellets can be ground down in the bird's gizzard and the lead absorbed into the bloodstream. Lead is a non-specific toxin, affecting most body systems. Ingestion is fatal in some but not all cases, its toxicity varying according to a range of factors. Most frequently, birds die of chronic lead poisoning two to three weeks after ingesting a small number of lead pellets. Birds dying will exhibit signs such as severe weight loss, green watery faeces and a green stained vent, general weakness and an inability to hold up wings or tail. Sick birds usually die of starvation due to paralysis of the intestinal muscles. Even if lead poisoning does not kill waterfowl directly, they may become vulnerable to disease and predation or may not be able to successfully reproduce.
How Lead Poisoning is Measured
The International Wetlands Research Bureau (IWRB) has widely studied the lead poisoning problem in waterfowl across Europe and America and published what are now internationally accepted indicators used to measure lead exposure and/or poisoning in waterfowl. These are summarised in Table1.
|Blood Level (ug/dl)||less than 25||25 to 40||more than 40|
|Liver Lead (mg/kg ww t)||less than 2||2 to 6||more than 6|
|Bone Lead (mg/kg dw t)||less than 10||10 to 20||more than 20|
The values shown have come from studies of experimentally treated captive birds, birds collected from the wild showing symptoms of poisoning and from work done on other species.
The American Approach
The Americans initially approached the issue of lead poisoning on a site by site basis, although all USA is now non-toxic shot only. Their decision criteria for determining non-toxic shot zones from 1985 onwards (see Table 2) used a combination of actual uptake of pellets (pellets in gizzard) with any one of the other IWRB criteria (see Table 1)
The American criteria were developed for use in determining non-toxic shot zones, the "hotspot" approach, hence the emphasis on use of indicators of short-term lead accumulation - blood and liver, in conjunction with direct evidence of shot ingestion - pellets in gizzards. From these results you could be pretty sure they were representative of the swamp where the birds were shot and therefore localised restrictions could be introduced if required.
In the USA today, the use of localised restrictions has been abandoned and non-toxic shot is mandatory for all waterfowl hunting.
|Gizzard (ingested shot)||1 or more pellets in 5% of a sample|
|Liver (lead content)||2 mg/kg or more lead in 5% of a sample|
|Blood (lead content)||0.2 ppm lead or more in 5% of a sample|
|40ug/dl lead or more in 5% of a sample|
The Victorian Experience
During the period 1992 to 1994 the then Victorian Field and Game Association undertook a number of independent research projects looking for first hand evidence of lead effects in Victorian waterfowl. The studies looked for pellet ingestion in gizzards and elevated lead levels in liver tissue of Black Duck, a species considered to be vulnerable to lead poisoning. Other studies were done to measure pellet densities in lake and swamp sediment. The samples collected were analysed at a suitably accredited and independent scientific laboratory and the results published by the Association. A little earlier, DPI had published data on accumulated lead in duck's wing bones collected by hunters across the state and on a localised study at Lake Buloke.
VFGA's sampling showed that at Lake Buloke, for instance, just on 5% of Black Duck sampled had ingested one or more pellets and the same percentage exhibited elevated lead levels in their livers.
The results from samples collected from around 40 other areas across the state varied, but it was certainly obvious that pellet ingestion and therefore poisoning, was occurring. It also needs to be remembered that Black Duck are only "mid-range" in susceptibility to poisoning. Other diving species, such as Hardhead and Blue Bills, are more susceptible due to their feeding habits, but very difficult to sample in as large numbers. What samples were available, showed worse results.
The figure of 5% of a sample being the accepted threshold for change is not based on hard scientific or biological evidence, it is a value judgement which has been agreed elsewhere by wildlife managers and hunters as being the point at which potential poisoning losses should be regarded as unacceptable. In the absence of scientific evidence to the contrary, it is difficult to argue against the acceptance of the American and IWRB decision criteria for Victoria.
Many hunters can recall where a "sick" duck was passed around during a plucking session and the wasted breast and green tinged flesh at the vent was observed and thought no more about. We know now what it was.
Don't expect to find a dead, lead poisoned duck floating past your decoys, as like all sick animals, they seek seclusion to die and are then quickly removed by predators.
All hunters share a certain frustration over the way hunting and firearm use is constantly under the microscope and appreciate how easy it is to assume that the move to non-toxic shot is part of that. This is not the case, otherwise the program would not have the support of leading hunting organisations and the Victorian Hunting Advisory Committee. Hunting is an activity, which relies strongly on demonstrating to the community that a very high level of morality and ethics exists among the participants. On that basis, now that the case against lead is established, it would be wrong to condone any continued long-term use of lead shot for waterfowl hunting.