4.5. Genetic background of captive lesser white-fronted goose stock

One of the three captive lesser white-fronted goose stocks used for reintroduction/restocking in Finland and Sweden was sampled to study the genetic background of the captive lesser white-fronted geese (IV). The founders of the Finnish captive lesser white-fronted goose stock came from a Swedish farm, although some individuals were subsequently transported directly from Central Europe (Markkola et al. 1999). The founders of the Swedish stock originated from wildfowl farms in Central Europe (von Essen 1996) and there has been a regular exchange of individuals between different farms. Therefore, the composition of all the present stocks is similar. Of the 15 captive individuals analysed, three were of the same mitochondrial haplotype (W1) as 81% of the wild Fennoscandian breeders and eight captive individuals were of the eastern main haplotype (E1) (see also 4.4). However, the remaining four captive individuals were shown to carry a haplotype, which is 0.45% (1 nucleotide substitution) different from a haplotype found in another goose species, the white-fronted goose. Two possible explanations exist for the occurrence of the white-fronted goose type mtDNA in the captive stock of lesser white-fronted goose. First, white-fronted goose type mtDNA could be present also in the wild lesser white-fronted goose either due to a recent divergence of the species or as a consequence of hybridization under natural conditions. However, as this was not detected in the natural populations (II, III) it can be concluded that hybridization is not very common (at least between female white-fronted and male lesser white-fronted geese) or, if it occurs, it does not lead to introgression of the mtDNA (i.e. restricted to first-generation hybrids in natural conditions). Therefore, a more plausible explanation is that hybridization has occurred during the history of lesser white-fronted goose captive breeding.

The existence of the mtDNA of the white-fronted goose in the captive stock of the lesser white-fronted goose indicates that hybridization has taken place, but does not reveal the degree of introgression. In the absence of pedigree records and other documentation it is impossible to estimate the composition of their nuclear genomes. Because females are the heterogametic sex (ZW) in avian species, it can be reasoned that all captive females carrying the mtDNA of the white-fronted goose also have the W chromosome of the white-fronted goose. On the other hand, any individual in the stock may carry heterospecific nuclear alleles (irrespective of the mtDNA type), because mtDNA and nuclear alleles have different transmission pathways. To assess further the proportion of heterospecific alleles in the stock, the stock should be also analysed with species-specific nuclear markers.

According to the guidelines of the Re-introduction Specialist Group of the IUCN’s Species Survival Commission (Kleiman et al. 1994, IUCN 1995), the stock used for reintroduction should be similar to the original wild stock to enhance the possibilities of survival and, on the other hand, to prevent the introduction of alien genes to wild populations and possible outbreeding depression. Because the Swedish reintroduction area in Svaipa, Swedish Lapland, is situated within a dispersal range from the breeding areas of the wild lesser white-fronted goose in Norwegian and Finnish Lapland, it would be wise to apply a precautionary principle to avoid possible harmful effects to the remaining wild breeding population. Some individuals released in Sweden have been observed in Finland and Norway, and the possibility of mixing of the wild and released birds with a captive origin is a realistic threat.

In addition to the probable genetic incompatibility of the captive stock, other unresolved obstacles exist for the use of reintroduction or restocking as a successful conservation measure. One of the preconditions for a species reintroduction is that the original causes of extinction or population decline have been removed (Kleiman et al. 1994, IUCN 1995). Despite attempts to protect key-areas and irrespective of the protected status of the lesser white-fronted goose in most countries, the species continues to be hunted. In the Swedish reintroduction project the hunting pressure has been diminished by changing the migration routes to safer areas by using semi-captive barnacle geese as foster parents. Unfortunately, the use of heterospecific foster-parents has led to imperfect imprinting and mixed identity of the goslings, which in turn has led in attempts to pair and hybridise with other goose species (von Essen 1999). During the Finnish restocking project the most prominent problem was that the released individuals joined flocks of bean geese (in the absence of learned migration routes) and were not imprinted to the release area. As a consequence, the resightings were scattered to various wintering localities (within and outside the natural range) and very few individuals returned to the release area (Markkola et al. 1999). With regards to the protection of wild populations, the problems in the reintroduction/restocking attempts much centre on the migratory programme of the species. Similarly, it has been shown in other species introductions that the migratory behaviour is the only life-history trait that correlates negatively with introduction success (Veltman et al. 1996). The experiences within the lesser white-fronted goose project suggest that even if an appropriate captive stock exists for reintroduction/restocking, the means for carrying out such conservation efforts are presently unavailable.