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Large-scale releases of native species: the mallard as a predictive model system
Kristianstad University, School of Education and Environment, Avdelningen för Naturvetenskap. Sveriges lantbruksuniversitet.ORCID iD: 0000-0003-1212-6607
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Human alteration of natural systems, and its consequences are of great concern and the impact on global ecosystems is one of the biggest threats that biodiversity stands before. Translocations of invasive species, as well as intraspecific contingents with non-native genotypes, whether they are deliberate or unintentional, are one such alteration and its consequences are continuously being assessed. The mallard (Anas platyrhynchos) is the most numerous and widespread duck in the world and a flagship in wetland conservation. It is also an important game species which is heavily restocked for hunting purposes, especially in Europe where over three million ducklings are released every year. Because of its hunted status, its abundance, and the number of released individuals, it can serve as a model species to study effects of releases, both for conservation and restocking for hunting, on wild populations. In this thesis the status of the mallard was assessed in the Nordic countries and the effects of releases on the wild populations were studied by mining historical ringing data, comparing morphology of present-day wild, farmed, and historical mallards, and analyzing phylogeography of wild and farmed mallards in Europe. The status of the mallard population in the Nordic countries are generally good, however, a joint effort of European countries is needed to monitor and manage the population. A significant difference between wild and farmed mallards concerning longevity, migration, bill morphology and genetic structure was also found, together with signs of cryptic introgression of farmed genotypes in the wild population with potential fitness reduction as a result. The effect is however limited by that only a fraction of released farmed mallards reach the breeding season due to low survival. A natural captive environment is crucial to keep individuals wild-like with high survival rates after release. However, with an introgression of potentially maladapted farmed genotypes leading to a reduction in fitness, a low survival of released mallards would favor the wild population. A legislative change regarding obligation to report numbers, provenance, and release sites of farmed mallard should be considered, together with practical solutions of ringing and genetic monitoring of released mallards.

Place, publisher, year, edition, pages
Umeå: Sveriges Lantbruksuniversitet, 2015.
Series
Acta Universitatis agriculturae Sueciae, ISSN 1652-6880 ; 2015:25
National Category
Zoology Fish and Wildlife Management
Identifiers
URN: urn:nbn:se:hkr:diva-13751ISBN: 978-91-576-8248-2 (print)ISBN: 978-91-576-8249-9 (print)OAI: oai:DiVA.org:hkr-13751DiVA: diva2:799187
Available from: 2015-03-30 Created: 2015-03-30 Last updated: 2017-05-03Bibliographically approved
List of papers
1. The status of the Nordic populations of the Mallard (Anas platyrhynchos) in a changing world
Open this publication in new window or tab >>The status of the Nordic populations of the Mallard (Anas platyrhynchos) in a changing world
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2013 (English)In: Ornis Fennica, ISSN 0030-5685, Vol. 90, no 1, 2-15 p.Article in journal (Refereed) Published
Abstract [en]

Dabbling ducks (Anas spp.) are importantmigratory quarry species, protected as a shared resource under international legislation. However, there is a lack of sufficient high-quality data on vital demographic rates and long-term trends in numbers to judge the conservation status of many duck populations at the flyway level. In response to reported declines in the North-West European flyway population of theMallard, we compiled available data on this species in the Nordic countries up to 2010. Generally, national breeding numbers showed increasing trends, wintering abundance showed variable trends, and productivitymeasures indicated stable or increasing trends.Major knowledge gaps were identified, namely the size of hunting bags, the influence of the released Mallards and the role of short-stopping in explaining changing patterns of wintering abundance across the North-West European flyway. Numerically the Nordic breeding population appears in “good condition”, and the wintering numbers have been either stable or increasing in the last two decades. The annual number of releases needs to be determined in order to judge the sustainability of the current levels of exploitation. Overall, none of the indicators showed alarming signs for the Mallard population in the Nordic countries when considered in isolation. However, the widespread decline in wintering numbers elsewhere across North-western Europe requires urgent pan-European action.

National Category
Zoology
Identifiers
urn:nbn:se:hkr:diva-10140 (URN)000317947800002 ()
Available from: 2013-02-05 Created: 2013-02-05 Last updated: 2017-05-03Bibliographically approved
2. Longevity and migration distance differ between wild and hand-reared mallards Anas platyrhynchos in Northern Europe
Open this publication in new window or tab >>Longevity and migration distance differ between wild and hand-reared mallards Anas platyrhynchos in Northern Europe
2013 (English)In: European Journal of Wildlife Research, ISSN 1612-4642, E-ISSN 1439-0574, Vol. 59, no 2, 150-166 p.Article in journal (Refereed) Published
Abstract [en]

The mallard Anas platyrhynchos is the world’s most widespread and numerous dabbling duck. It is also farmed and released to the wild by the millions each year, but the effects of this on wild populations remain little studied. By using historical national ringing–recovery data from Sweden and Finland, we here address three predictions based on previous studies: (1) longevity is higher in wild than in hand-reared mallards, (2) wild mallards migrate longer than hand-reared, and (3) migration distance in wild ducks surviving long enough to start fall migration has decreased over the last 50 years. Indeed, wild mallards lived longer than hand-reared (19 versus 9 months in Swedish birds and 13 versus 4 months in Finnish birds). Compared to wild mallards, a smaller proportion of hand-reared birds survived long enough to have the chance to enter the wild breeding population; less than 25 % of the Swedish birds and less than 10 % of the Finnish birds lived a year or longer. Wild birds migrated farther than hand-reared (mean distance in Swedish birds, 676 versus 523 km; in Finnish birds, 1,213 versus 157 km), a pattern caused by both shorter life span and lower migration speed in hand-reared birds. Mean migration distance in wild Swedish mallards was 787 km in 1947–1972 but 591 km in 1977–1993. This difference was not statistically significant, though, possibly due to the limited sample size and lack of data from the last two decades. In general, our study provides a conservative test of the predictions addressed, calling for more research about the consequences of restocking duck populations.

Keyword
Duck, Migration, Mortality, Restocking, Short-stopping, Survival
National Category
Zoology
Identifiers
urn:nbn:se:hkr:diva-9935 (URN)10.1007/s10344-012-0660-0 (DOI)000316330500004 ()
Available from: 2012-12-18 Created: 2012-12-18 Last updated: 2017-05-03Bibliographically approved
3. Wild mallards have more ‘‘goose-like’’ bills than their ancestors: a case of anthropogenic influence?
Open this publication in new window or tab >>Wild mallards have more ‘‘goose-like’’ bills than their ancestors: a case of anthropogenic influence?
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2014 (English)In: PLoS ONE, ISSN 1932-6203, Vol. 9, no 12, e115143Article in journal (Refereed) Published
Abstract [en]

Wild populations of the world’s most common dabbling duck, the mallard (Anas platyrhynchos), run the risk of genetic introgression by farmed conspecifics released for hunting purposes. We tested whether bill morphology of free-living birds has changed since large-scale releases of farmed mallards started. Three groups of mallards from Sweden, Norway and Finland were compared: historical wild (before large-scale releases started), present-day wild, and present-day farmed. Higher density of bill lamellae was observed in historical wild mallards (only males). Farmed mallards had wider bills than present-day and historical wild ones. Present-day wild and farmed mallards also had higher and shorter bills than historical wild mallards. Present-day mallards thus tend to have more “goose-like” bills (wider, higher, and shorter) than their ancestors. Our study suggests that surviving released mallards affect morphological traits in wild population by introgression. We discuss how such anthropogenic impact may lead to a maladapted and genetically compromised wild mallard population. Our study system has bearing on other taxa where large-scale releases of conspecifics with ‘alien genes’ may cause a cryptic invasive process that nevertheless has fitness consequences for individual birds.

National Category
Ecology
Identifiers
urn:nbn:se:hkr:diva-13321 (URN)10.1371/journal.pone.0115143 (DOI)000349146300038 ()25514789 (PubMedID)
Funder
Swedish Environmental Protection Agency
Available from: 2014-12-22 Created: 2014-12-22 Last updated: 2017-05-03Bibliographically approved
4. Released game birds cause continent-wide introgression: a changing genetic landscape in European mallard (Anas platyrhynchos)
Open this publication in new window or tab >>Released game birds cause continent-wide introgression: a changing genetic landscape in European mallard (Anas platyrhynchos)
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(English)Manuscript (preprint) (Other academic)
National Category
Zoology
Identifiers
urn:nbn:se:hkr:diva-13750 (URN)
Available from: 2015-03-30 Created: 2015-03-30 Last updated: 2017-05-03Bibliographically approved

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