To evaluate duck harvest sustainability, we need to evaluate population size and production rate, in addition to harvest bag size. However, these statistics are inadequate in Europe. We only have a robust evaluation of the wintering population size of ducks. Finland and Czech are the only countries conducting annual brood production surveys for ducks. Only Denmark annually collects harvest wing samples at a national level. In Finland, wing samples have been collected for a few years only. Nearly every European country produces some kind of bag statistics, but data quality is often poor. In addition, methods differ from one country to another, so comparing the results is difficult.
Finland is the only country along the East-Atlantic flyway that conducts annual brood surveys.
All individuals are not equal in their population growth rates. Many juvenile birds die before they reach their first breeding season. Old birds are thus more important for the population than young ones. This is why harvest should be targeted at young individuals. In years of poor breeding success, the ratio of young birds is lower compared to old ones, and thus the harvest bag should be decreased to reach a sustainable harvest level.
In addition to species, wings can also be used to determine the age and sex of ducks.
Finland and Denmark both belong to the East-Atlantic flyway. Finland is an important breeding area for several duck species. Ducks born in Finland often migrate through Denmark, while some also winter there. In a recently published study, brood production in Finland was compared to harvest bag size and wing age ratios in Finland and Denmark. Three common duck species were included in the study: the common teal (Anas crecca), Eurasian wigeon (Mareca penelope) and common goldeneye (Bucephala clangula).
Denmark collects harvested wings on an annual level, while two periods of three-year surveys have been organised in Finland.
The study showed that the annual harvest of Finnish goldeneyes is positively correlated with their reproductive output. Additionally, the increase in brood production suggested to associate with an increase in juvenile wing ratio in the harvest bag. But, as the sample size is only six years, this result remains uncertain. This is a good start towards sustainable harvest levels. No similar association was observed for teal and wigeon. However, the wigeon harvest in Denmark increased with an increasing juvenile ratio. This study was unable to evaluate sustainable harvest levels as such. Finnish brood surveys show long-term declining trends for all the studied species, and harvest levels in Finland have concurrently dropped. However, only harvest levels of goldeneye have decreased in Denmark.
This study emphasises a need to better define population units, before harvest sustainability can be assessed. Our current knowledge is not enough to say whether duck harvest is sustainable even in Northern Europe. With declining brood production trends, we urgently need to follow how well the harvest reflects this population change.
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