Environmental Engineering Reference
In-Depth Information
may be real. Although the annual economic costs of exotic fi shes in the USA has
been estimated at US$5.4 billion, sports fi shing contributes more than ten times
that value to the US economy and a substantial proportion of that industry is based
on game fi shing for locally non-indigenous fi shes. Exotic salmonids have estab-
lished world-renowned game fi sheries in New Zealand in the absence of suitable
native game species, despite substantial ecological damage to indigenous fi sh and
aquatic invertebrate communities (McDowall 2006). Cost:benefi t tradeoff s are
common for most globally important invasive fi shes. Common carp is one of the
most widespread freshwater species and is responsible for signifi cant ecological and
economic damage worldwide, yet it also contributed 2.8 million tonnes to global
aquaculture production in 2000 (FAO 2003).
13.2 The role of humans
The intentional translocation of freshwater fi sh is not exclusively a modern phe-
nomenon. Although most introductions worldwide have occurred since the mid-
19th century, the introduction and redistribution of common carp in Europe
dates as far back as the 12th or 13th centuries (Witkowski 1996). A large propor-
tion of the freshwater fi sh fauna of the UK and Ireland is non-native and has been
introduced from mainland Europe since the 15th century. The role of deliberate
human transport in the introduction and spread of non-indigenous fi shes is quite
clear. In the USA, human population density is correlated with non-native fi sh
diversity, although the relationship is complicated by the prolonged deliberate
release of game fi sh species by state agencies into wilderness areas with compara-
tively low population density (McKinney 2001). The same is true in New Zealand,
where the distribution of species such as perch, rudd, and tench, most commonly
spread illegally by coarse fi shing enthusiasts, is concentrated close to major popu-
lation centres, whereas game fi sh salmonids are far more widely distributed due
to historical legalized release by Acclimatization Societies and subsequent natural
dispersal. Human access, as well as proximity to concentrations of human popu-
lation, is important to the risk of initial release and also to re-invasion following
the eradication of non-indigenous fi shes. A UK study found that the probability
of human introduction of fi sh to ponds was correlated with at least two of the
following variables: distance to nearest road, nearest footpath, or nearest pond
( et al . 2005a).
h e introduction of game fi sh species for recreational purposes not only causes
direct impacts on indigenous fauna by predation or competitive displacement,
but may also encourage other destructive practices such as the transfer and spread
of suitable bait fi sh to game fi sh waters. In New Zealand, the widespread transfer
of salmonids to lentic water bodies was accompanied by the release of indigenous
prey species, such as smelt and eleotrids, to waters where these species did not nat-
urally occur. h is has caused the demise or local extinction of genetically distinct
populations of other indigenous species (McDowall 2006).
 
 
Search WWH ::




Custom Search