Environmental Engineering Reference
In-Depth Information
Mammals should also be given the opportunity to
acquire the necessary information to enable survival in
the wild, and soft releases are therefore recommended.
Mammals propagated in an enclosure tend to develop
an affi nity for their immediate surroundings and there-
fore, upon release, exhibit a slow dispersal rate. This
behaviour generally enhances survival. An example of
a successful soft release is the case of the scimitar-
horned oryx (
Oryx dammah
) in Tunisia, which had
disappeared from that country in 1902 due to deserti-
fi cation, competition with domestic livestock, habitat
disturbance and, of course, hunting. In December
1985, fi ve males and fi ve females were reintroduced
from a zoo in Britain into the Bou-Hedma National
Park, which is a 2400-ha fenced area that has been
protected from domestic livestock since 1977. They
were acclimatized in a 600-m
2
pen for 4.5 months and
then released into a 10-ha pre-release enclosure. Social
organization was established peacefully, and the oryx
adjusted to the new climate and natural foods. In July
1987, the oryx were released from the enclosure into
the park (Bertram 1988). In 2005 there were 130
animals in the park while, sadly, the species has gone
globally extinct in the wild.
Sometimes spectacular or what might be called
'heroic' techniques are indeed the only solution to
achieve a reintroduction. In a translocation project for
the North American beaver (
Castor canadensis
) in
Idaho, for example, the mountains, heavy forests and
lack of roads made transplanting a labour-intensive,
expensive and time-consuming task (Heter 1950). In
addition, it resulted in high beaver mortality. The use
of planes and parachutes with animal-holding boxes
proved to be a much more effi cient and less expensive
method of transportation (Heter 1950). In 1948, 76
live beavers were dropped with only one casualty.
Observations made in 1949 showed that the beavers
that had participated in the airborne transplantation
had settled and were well on their way to producing
colonies (Heter 1950). At present beavers range widely
and in great numbers in the state of Idaho.
There have been quite a few attempts to reintroduce
large carnivorous mammals in areas from which they
were
extirpated
, or disappeared, among them wolf,
bear, wild dog and lynx. Reintroduction of large carni-
vores is always very diffi cult. They require extensive,
high-quality areas, with substantial prey for which
they may compete with humans. In addition, as dis-
cussed in section 8.7, they are associated with depreda-
tion of livestock in many people's minds (Stahl
et al
.
2001), and some people may also feel uncomfortable
when large predators are reintroduced into their
neighbourhoods (see Hayward & Somers 2009). Nev-
ertheless reintroductions can be successful and, as an
example, an overview of the reintroduction attempts
of the European lynx (
Lynx lynx
) is given in Table 8.1.
To summarize, in the past 37 years, lynx reintroduc-
tions have been carried out at 15 different sites in eight
countries. Of these, fi ve were successful, four are of
uncertain status and six clearly failed. In an analysis
of these reintroductions, Linnell
et al
. (2009) con-
cluded that, in most cases, basic rules had been vio-
lated: bad planning, widespread use of captive-born
lynx, no attention being paid to genetic origin, very
little pre-release site evaluation carried out and very
small numbers (in one case, only two males) reintro-
duced. Despite these
ad hoc
attempts, the reintroduc-
tion of the lynx in Europe has become a success and,
together with natural expansion of the species, the dis-
tribution of the lynx in central and eastern Europe has
enormously increased.
There have been quite a number of succesful
mammal reintroductions. Part of this success can be
attributed to opportunistic dispersal characteristics and
a high reproduction rate.
8.6 ECOSYSTEM EFFECTS OF
REINTRODUCTION ATTEMPTS
The Great Lakes ecosystem in the midwestern United
States has changed dramatically over the past 50 years.
A review of historical changes reveals complex inter-
actions of overfi shing, invasion by non-indigenous
species, eutrophication, extensive habitat modifi cation
and toxic contamination. Native fi sh species that
required tributary or near-shore habitat for spawning
and nursery areas have declined markedly. Among sur-
viving
native species
, such as walleye (
Stizostedion
vitreum
), stock diversity declined with the loss of
tributary - spawning stocks and lake - spawning stocks
became dominant. With the rarefaction of native
species, the abundance of formerly subdominant
species increased. Species such as smelt (
Osmerus
mordax
), gizzard shad (
Dorosoma cepedianum
) and white
perch (
Morone americana
) depend less on critical tribu-
tary and near-shore habitat (Koonce
et al
. 1996 ). It
seems that a complete restoration of the Great Lakes is
unlikely, due to naturalization of exotic species, habitat
degradation and destruction, urbanization of many of
