Environmental Engineering Reference
In-Depth Information
demonstration of this phenomenon is in those states where settlers regarded
endemic local species as undesirable for food or sport (Rahel 2000). Similar faunal
homogenization in the Iberian Peninsula has resulted from the spread of both
exotic fi sh and translocated native species (Clavero and Garcia-Berthou 2006).
Restricting the transfer and release of native fi shes presents particular diffi culties
since it by-passes the rigorous biosecurity provisions at the international border.
Many countries have legislation to prohibit the release of live aquatic life to waters
where that species does not occur naturally, but law enforcement is diffi cult. Even
if a species is already present, the introduction of individuals from other popula-
tions may signifi cantly homogenize genetic diversity. Laws that prohibit interstate
transport of fi sh and other aquatic life may help, however, river drainages are typ-
ically not confi ned within state, or even national boundaries, and natural spread
throughout a river drainage can be expected. Signifi cant natural barriers to fi sh
passage assist in preventing natural spread and illegal releases. For instance, the
importation to Tasmania from mainland Australia of any fi sh capable of living in
Tasmanian waters is prohibited, as is any transfer of live aquatic life between the
islands of New Zealand (with the exception of tropical or ornamental aquarium
species). In many cases these laws were originally enacted to protect exotic sports
fi sheries from the spread of disease and inferior stocks although they now serve to
protect natural biogeography and genetic diversity.
Although most studies of ballast water have found few adult fi sh or larvae, bal-
last water is still a potentially important route of introduction for invasive fi sh.
Ecologically and economically destructive invasions attributable to ballast water
include the sea lamprey and round goby introduced to the Laurentian Great Lakes.
Fish most likely to establish as a result of ballast water transport are small-bodied
crevicolous species, especially gobies and blennies (Wonham
et al
. 2000). Such
species are also most likely to be transported in hull structures such as sea-chests
(Coutts and Dodgshun 2007) although the transport of their adhesive eggs,
spawned in the port of origin, in sea-chests and on the outside of ships' hulls, is
possibly a more likely mechanism than the transport of adult fi sh and is more likely
to increase the number of propagules introduced, thereby enhancing the risk of
establishment (Walsh
et al
. 2003). Post-larval fi sh may also be entrained with slow
moving, structurally-complex towed structures such as oil platforms as long as
those structures are not transported through waters hostile to their survival (Foster
and Willan 1979).
The annual trade in ornamental and aquarium fi sh exceeds 1 billion individuals
from around 4000 freshwater and 1400 marine species (Wittington and Chong
