Are wild animal populations in Sweden increasing or decreasing? It is difficult to count wild animals, but the quantity harvested by hunting gives an indication. Now these statistics can be made clearer and more useful, thanks to a new model developed by Swedish researchers to count the number of wild animals hunted.
“We believe this system will make statistics clearer and more reliable. The idea is that this model should be used from autumn, to present official statistics on the number of wild animals hunted in Sweden,” says Tom Lindström. associate professor in the Department of Physics, Chemistry and Biology (IFM) at Linköping University, who carried out the study in collaboration with Göran Bergqvist of the Swedish Association for Hunting and Wildlife Management.
Hunting is a way to get an overview of the size of wild populations. For some species, this is the only indicator we have. Knowing how many wild animals are harvested by hunting each year is therefore an important part of wildlife monitoring, which must be adapted to changes in the ecosystem.
For example , reporting of moose and large mammal hunting is required by law, but for most species, from jays to wild boar, reporting is optional. The Swedish Association for Hunting and Wildlife Management is responsible for annual statistics on the number of these animals captured. Hunting teams report how much they shot at around 50 species and how much land they hunted. But because reporting is optional and reporting is lacking for some Swedish hunting grounds, statistical methods are used to calculate the number of wildlife harvested from those blind spots not covered by reports from hunting teams. One of the important weaknesses of the method of analysis used so far is that it is very sensitive to low reporting, in particular for species whose hunting varies according to the hunting teams and which are, in general, little known. hunted. Tom Lindström gives an example:
“In 2015, the analysis seemed to show that many more beavers had been harvested than the years previous ones. However, when we analyzed the data, it turned out that the big difference was that only one hunting team reported shooting a single beaver. Because this method of analysis is so sensitive to single reports, it gave the impression that several thousand beavers had been shot at this club.”
For this reason, the researchers have developed a new analysis model that can give a better estimate of the number of wild animals of each species that are harvested each year. The study, published in the journal Ecological Indicators, consists of two parts. In the first part, the researchers analyzed various parameters and developed a model capable of describing the data. They then used the model to predict how many wildlife would be hunted in the area for which data was missing.
Analyses performed with the new model can help to better understand the hunting behavior in Sweden. In the study, researchers found that hunting teams that had larger hunting areas generally shot fewer animals per area. The correlation was similar for all hunted species. There may have been fewer animals in these areas, so a larger area is needed to have a chance of catching something – or there may be other explanations. Time is another piece of the puzzle. The researchers did something called auto-regressive modeling, which means that the analysis of hunting volume in an area takes into account volumes from previous years.
This new statistical framework solves several problems.
“The model presents the uncertainty of these analyzes honestly and shows a range, instead of a specific number. It is also less sensitive for individual hunting reports, which reduces the uncertainty of the analysis”, explains Tom Lindström.
The project was funded by the Association Swedish Hunting and Wildlife Management Agency and the Swedish Environmental Protection Agency. The calculation was performed on resources provided by the Swedish National Infrastructure for Computing (SNIC).