the north and central European lineages of S. trutta in official fish hatcheries. As a
result, there has been a shift to using lineages from different parts of central and
northern Europe (Araguas et al. 2009). Modern management practices have therefore
resulted in increased fish introductions during the past few decades with a maximum
during the 1990s (Fig. 8.1). As a result, trout have been introduced in most lakes
with higher fishing interest (e.g. lower altitude or bigger surface area). The low
number of lakes remaining without fish after the 1990s is likely the reason why fish
introductions dropped considerably during 2000.
8.3.2 Collateral Introductions
The salmonid introductions described above have resulted in collateral introductions of other fish species mainly used as live bait (Miró and Ventura 2015). This
fact may eventually lead to stronger ecological consequences than the introduction
of trout alone. In the Pyrenees, Miró and Ventura (2015) found that the introduction
of minnows in high mountain lakes was mediated by a preceding invasive species
and facilitated by human activity. They found that the introduction of the minnow is
a more recent and faster process than that of salmonids (Fig. 8.1). Since 1970, when
the first minnow introduction took place, it has now spread to 27% of the lakes of
the southern Pyrenees with an introduction rate of 4.7 lakes per year, compared to
those of trout, at 2.2 lakes per year for the period between 1940 and 2000 (Miró and
Ventura 2015).
Differences in minnow life history characteristics compared to those of trout give
them a higher acclimation success and therefore high invasive potential. The
minnow, like other small widely distributed freshwater fish, displays a remarkable
variability in its life history depending on the local temperature. For example,
minnows have maximum age ranges between 3 and 13 years reaching maturity
between 1–2 and 5–7 years in optimal and sub-optimal conditions respectively, and
show significantly lower growth increments in cold summers (Mills 1988). This
plasticity in their life history is what has allowed the species to easily acclimate to
high mountain lakes, showing higher resistance to harsh conditions than trout. Miró
and Ventura (2015) have not found any lake where minnows have disappeared once
established. In contrast, in lakes with trout, between 10 and 44% of the trout
populations have become extinct after 20–30 years due to a lack of favourable
conditions (Knapp 2005; Armstrong and Knapp 2004; Miró and Ventura 2013).
Moreover, in the Pyrenees, Miró and Ventura (2015) have found that in twenty
lakes and ponds, pre-existing trout populations have disappeared after minnow
introductions. Some of these lakes and ponds had brown trout introduced centuries
ago while others were stocked recently.
Miró and Ventura (2015) also found that minnow presence was more likely in
lakes with lower elevation, greater surface areas and higher temperatures. This
distribution could be a result of the pattern of introductions (e.g. fishermen using
live bait do not fish so often at the upper altitude lakes) or to fair habitat conditions
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M. Ventura et al.
result, there has been a shift to using lineages from different parts of central and
northern Europe (Araguas et al. 2009). Modern management practices have therefore
resulted in increased fish introductions during the past few decades with a maximum
during the 1990s (Fig. 8.1). As a result, trout have been introduced in most lakes
with higher fishing interest (e.g. lower altitude or bigger surface area). The low
number of lakes remaining without fish after the 1990s is likely the reason why fish
introductions dropped considerably during 2000.
8.3.2 Collateral Introductions
The salmonid introductions described above have resulted in collateral introductions of other fish species mainly used as live bait (Miró and Ventura 2015). This
fact may eventually lead to stronger ecological consequences than the introduction
of trout alone. In the Pyrenees, Miró and Ventura (2015) found that the introduction
of minnows in high mountain lakes was mediated by a preceding invasive species
and facilitated by human activity. They found that the introduction of the minnow is
a more recent and faster process than that of salmonids (Fig. 8.1). Since 1970, when
the first minnow introduction took place, it has now spread to 27% of the lakes of
the southern Pyrenees with an introduction rate of 4.7 lakes per year, compared to
those of trout, at 2.2 lakes per year for the period between 1940 and 2000 (Miró and
Ventura 2015).
Differences in minnow life history characteristics compared to those of trout give
them a higher acclimation success and therefore high invasive potential. The
minnow, like other small widely distributed freshwater fish, displays a remarkable
variability in its life history depending on the local temperature. For example,
minnows have maximum age ranges between 3 and 13 years reaching maturity
between 1–2 and 5–7 years in optimal and sub-optimal conditions respectively, and
show significantly lower growth increments in cold summers (Mills 1988). This
plasticity in their life history is what has allowed the species to easily acclimate to
high mountain lakes, showing higher resistance to harsh conditions than trout. Miró
and Ventura (2015) have not found any lake where minnows have disappeared once
established. In contrast, in lakes with trout, between 10 and 44% of the trout
populations have become extinct after 20–30 years due to a lack of favourable
conditions (Knapp 2005; Armstrong and Knapp 2004; Miró and Ventura 2013).
Moreover, in the Pyrenees, Miró and Ventura (2015) have found that in twenty
lakes and ponds, pre-existing trout populations have disappeared after minnow
introductions. Some of these lakes and ponds had brown trout introduced centuries
ago while others were stocked recently.
Miró and Ventura (2015) also found that minnow presence was more likely in
lakes with lower elevation, greater surface areas and higher temperatures. This
distribution could be a result of the pattern of introductions (e.g. fishermen using
live bait do not fish so often at the upper altitude lakes) or to fair habitat conditions
186
M. Ventura et al.