for released minnows to become established. Taking into account the high plasticity
of minnows, it seems more likely that their presence was a result of the pattern of
introduction. As well as minnows, other species might be used as live bait,
increasing the number of invasive species to lakes. This is the case for gudgeon
(Gobio spp.), which is now found in some lakes of the northern slope of the
Pyrenees (Miró 2011). This fish has similar size and flexible life history features to
those of minnows (Tang et al. 2011). Thus, the ecological effects of fish introductions in high mountain lakes can result in stronger unpredicted consequences.
Live bait-related introductions of minnows have occurred in lower, boreal and
arctic lakes where trout is present. The distribution of minnow expanded considerably throughout the twentieth century in the north European lakes of Scotland and
Norway, especially in mountain areas, due mainly to the use of minnows as live bait
for angling (Maitland and Campbell 1992; Museth et al. 2007). When minnow is
introduced in lakes with autochthonous trout, it reduces recruitment and annual
growth rates of trout, causing a decrease of the trout abundance by 35% on average;
however, the effect on other native fauna takes place primarily in the shallow littoral
areas (Museth et al. 2007).
Angling practices with live bait represents a worrying pathway for alien species
introductions (Kerr et al. 2005; Webb 2007; DiStefano et al. 2009; Ward et al.
2012). The largest organisms used as live bait are several species of small fishes,
but other animals such as amphibians, earthworms, crayfishes, grubs and insects are
also used (Lindgren 2006; Keller and Lodge 2007). Improper disposal of live bait
has been attributed as the source of introduction of at least 14 species of fishes in
Ontario (Kerr et al. 2005). In the English Lake District, individuals of at least 12
native and non-native fish species have been brought to Windermere for the purpose of live baiting (Winfield et al. 2011). Live bait use was also responsible for the
introduction of 47 known freshwater species in United States Mid-Atlantic slope
drainage systems, among which are at least 5 non-native fishes, 4 non-native
crayfishes and 9 non-native earthworm species (Kilian et al. 2012). Live baits may
be released to the medium by accidental escape or, more often, by purpose at the
end of the fishing trip (Winfield et al. 2011; Kilian et al. 2012). In some cases, it has
been shown that bait-related introductions have resulted in established populations
of invasive species (e.g. Callaham et al. 2006; Migge-Kleian et al. 2006).
In high mountain lakes, trout are the only species group authorised for introduction by governmental agencies worldwide (e.g. Sostoa and Lobón-Cerviá 1989;
Wiley 2003), mainly associated with recreational fishing (Cambray 2003). Unlike
trout, minnow introductions are in general not authorised by governmental
authorities, and their introduction is often an illegal angling practice. As mentioned,
the final result in many cases is that fish unused as live bait are released at the end of
the fishing expedition (Maitland and Campbell 1992; Kerr et al. 2005; Winfield
et al. 2011; Kilian et al. 2012). This practice has been quantified to be done by 36%
of the fishermen in Michigan and Wisconsin, 41% in Ontario and 65% in Maryland
(Litvak and Mandrak 1993; Kerr et al. 2005; Kilian et al. 2012). To prevent the
widespread release of non-native species used as live bait, many US states and
Canadian territories have restricted the use, sale or transport of bait (Kerr et al.
8 Why Should We Preserve Fishless High Mountain Lakes?
187
of minnows, it seems more likely that their presence was a result of the pattern of
introduction. As well as minnows, other species might be used as live bait,
increasing the number of invasive species to lakes. This is the case for gudgeon
(Gobio spp.), which is now found in some lakes of the northern slope of the
Pyrenees (Miró 2011). This fish has similar size and flexible life history features to
those of minnows (Tang et al. 2011). Thus, the ecological effects of fish introductions in high mountain lakes can result in stronger unpredicted consequences.
Live bait-related introductions of minnows have occurred in lower, boreal and
arctic lakes where trout is present. The distribution of minnow expanded considerably throughout the twentieth century in the north European lakes of Scotland and
Norway, especially in mountain areas, due mainly to the use of minnows as live bait
for angling (Maitland and Campbell 1992; Museth et al. 2007). When minnow is
introduced in lakes with autochthonous trout, it reduces recruitment and annual
growth rates of trout, causing a decrease of the trout abundance by 35% on average;
however, the effect on other native fauna takes place primarily in the shallow littoral
areas (Museth et al. 2007).
Angling practices with live bait represents a worrying pathway for alien species
introductions (Kerr et al. 2005; Webb 2007; DiStefano et al. 2009; Ward et al.
2012). The largest organisms used as live bait are several species of small fishes,
but other animals such as amphibians, earthworms, crayfishes, grubs and insects are
also used (Lindgren 2006; Keller and Lodge 2007). Improper disposal of live bait
has been attributed as the source of introduction of at least 14 species of fishes in
Ontario (Kerr et al. 2005). In the English Lake District, individuals of at least 12
native and non-native fish species have been brought to Windermere for the purpose of live baiting (Winfield et al. 2011). Live bait use was also responsible for the
introduction of 47 known freshwater species in United States Mid-Atlantic slope
drainage systems, among which are at least 5 non-native fishes, 4 non-native
crayfishes and 9 non-native earthworm species (Kilian et al. 2012). Live baits may
be released to the medium by accidental escape or, more often, by purpose at the
end of the fishing trip (Winfield et al. 2011; Kilian et al. 2012). In some cases, it has
been shown that bait-related introductions have resulted in established populations
of invasive species (e.g. Callaham et al. 2006; Migge-Kleian et al. 2006).
In high mountain lakes, trout are the only species group authorised for introduction by governmental agencies worldwide (e.g. Sostoa and Lobón-Cerviá 1989;
Wiley 2003), mainly associated with recreational fishing (Cambray 2003). Unlike
trout, minnow introductions are in general not authorised by governmental
authorities, and their introduction is often an illegal angling practice. As mentioned,
the final result in many cases is that fish unused as live bait are released at the end of
the fishing expedition (Maitland and Campbell 1992; Kerr et al. 2005; Winfield
et al. 2011; Kilian et al. 2012). This practice has been quantified to be done by 36%
of the fishermen in Michigan and Wisconsin, 41% in Ontario and 65% in Maryland
(Litvak and Mandrak 1993; Kerr et al. 2005; Kilian et al. 2012). To prevent the
widespread release of non-native species used as live bait, many US states and
Canadian territories have restricted the use, sale or transport of bait (Kerr et al.
8 Why Should We Preserve Fishless High Mountain Lakes?
187