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W. Nentwig
phus, cattle and sheep are also susceptible to this parasite (Drozdz et al.
2003).
Rabbits (Oryctolagus cuniculus) originate from Spain. In mediaeval times,
monks and noblemen spread them to France and other European countries
and, in the 12th century, to England. Some domestication occurred but escaping
specimens naturalized easily and built up large game populations. British
colonists brought rabbits into Australia in 1788 and later into New Zealand,
primarily to shoot as game. Rabbits have been released on more than 800
islands throughout the world (Thompson and King 1994). When rabbits
became a pest in Australia, the Myxomatosis virus was introduced into Australia
and other countries to control them. Later, the disease also reduced the
native rabbit populations in Spain, France and Italy but, as game compensation,
the North American Eastern cottontail Sylvilagus floridanus was introduced
into these countries.
Probably since Roman times, common pheasants (Phasianus colchicus),
native to Asia, have been introduced to many European countries for game
but could not establish self-maintaining populations in most areas due to
unfavourable climatic conditions. Since pheasants are a favourite game bird
throughout Europe, millions are bred and released each year. This means that
the small naturalized populations of mixed genetic origin are maintained
only by large releases, also of different origins. In the UK, for example, 20 million
pheasants are released annually, 12 million of which are shot (150
birds km –2 ), the remaining 8 million birds dying probably due to predator
pressure, diseases and insufficient food. Hunting for pheasants is an industry
which annually generates over £ 300 million and sustains 26,500 jobs (Tapper
1999).
2.3.1.3 Release of Fish and Other Species
It is a widespread habit for anglers to introduce fish into their waters, with the
aim of increasing catch volume or improving the attractiveness of their catch.
Since fish survival depends primarily on water quality and environmental
structure, many blue white fish never got established – despite enormous
stocking, higher yields were not achieved. However, repeated restocking of
millions of specimens yielded a mix of species and genetic origins throughout
the fishing sites, introduced new species or varieties, and offered access of
parasites and disease to hitherto healthy populations.
One of the most prominent cases concerned is that of the rainbow trout
Oncorhynchus mykiss, native to the Pacific coast river systems of North America.
It was first introduced to British rivers in 1874, later to all European river
systems, and belongs now to the 100 world’s worst invaders (ISSG 2006). It has
more tolerance to polluted waters, poor diet, and stress, and has consequently
replaced the native brown trout Salmo trutta which requires higher-quality