changes in fish communities in French rivers have shown that climate change
is already affecting their composition [40], particularly in large rivers where the
proportion of warm water and southern species is increasing substantially [41].
Compared to the other large French rivers, the trend observed on the Seine River
is more equivocal in so far as the species whose abundance has increased in recent
decades include both warm water (e.g. bitterling, pumpkinseed and wels catfish) and
cold water fish (e.g. European bullhead and dace) [38]. In the Seine River, the
improvement in water quality has allowed the return of rheophilic and oxyphilic
species, which are often also cold water species, undoubtedly leading to a blurring of
the effect of global warming.
7 Conclusion and Perspectives
The results described above suggest that long-term changes in fish communities in
the Seine River basin are driven by multiple factors operating at different spatial
and temporal scales. Overall, the most significant trends concern (1) a constantly
increasing establishment of new exotic species; (2) a dramatic decline in migratory
fish until the extinction of several species during the twentieth century, followed by a
significant but still limited recovery process over the last two decades; (3) and more
locally, changes in species composition of communities that vary according to the
context of anthropogenic pressures. In particular a severe deterioration in the state of
fish populations occurred in the most human-impacted large rivers until the 1970s,
followed by a partial recovery following the implementation of effective measures to
control domestic and industrial pollutions.
In this respect, the changes observed in the Seine River basin are quite similar to
those observed in other European river basins strongly marked by the density and
intensity of human activities, such as the Rhine, the Thames, the Spree in Berlin
or the Lambro in Milan [42–45]. All these rivers have indeed experienced an
increase in exotic species, a massive decline in intolerant species, especially migratory species, compared to the preindustrial period and, in recent times, evidence of
recovery with the development of pollution control policies.
The colonisation of rivers by exotic fish species is a global phenomenon, particularly acute in Europe, which continues to rise [46]. Considering that the spread of
alien species is favoured by the globalisation of the circulation of people and
commodities and by the artificialisation of ecosystems [47], it is very unlikely that
the arrival of new exotic species on the Seine River basin will decline, at least for the
next few decades. If the colonisation rate of alien species continues at its current
level (and even more so if it keeps increasing), the number of non-native species
noted in the Seine River basin could quickly exceed the number of native species.
In the 2000s, an established population of Misgurnus anguillicaudatus was
identified in an ornamental pond in Paris (eradicated since then). This weather
loach, native of East Asia, is frequently used as food or aquarium fish and has
been recently detected in several European countries [48]. More recently, in 2016, a
Changes in Fish Communities of the Seine Basin over a Long-Term Perspective
317
is already affecting their composition [40], particularly in large rivers where the
proportion of warm water and southern species is increasing substantially [41].
Compared to the other large French rivers, the trend observed on the Seine River
is more equivocal in so far as the species whose abundance has increased in recent
decades include both warm water (e.g. bitterling, pumpkinseed and wels catfish) and
cold water fish (e.g. European bullhead and dace) [38]. In the Seine River, the
improvement in water quality has allowed the return of rheophilic and oxyphilic
species, which are often also cold water species, undoubtedly leading to a blurring of
the effect of global warming.
7 Conclusion and Perspectives
The results described above suggest that long-term changes in fish communities in
the Seine River basin are driven by multiple factors operating at different spatial
and temporal scales. Overall, the most significant trends concern (1) a constantly
increasing establishment of new exotic species; (2) a dramatic decline in migratory
fish until the extinction of several species during the twentieth century, followed by a
significant but still limited recovery process over the last two decades; (3) and more
locally, changes in species composition of communities that vary according to the
context of anthropogenic pressures. In particular a severe deterioration in the state of
fish populations occurred in the most human-impacted large rivers until the 1970s,
followed by a partial recovery following the implementation of effective measures to
control domestic and industrial pollutions.
In this respect, the changes observed in the Seine River basin are quite similar to
those observed in other European river basins strongly marked by the density and
intensity of human activities, such as the Rhine, the Thames, the Spree in Berlin
or the Lambro in Milan [42–45]. All these rivers have indeed experienced an
increase in exotic species, a massive decline in intolerant species, especially migratory species, compared to the preindustrial period and, in recent times, evidence of
recovery with the development of pollution control policies.
The colonisation of rivers by exotic fish species is a global phenomenon, particularly acute in Europe, which continues to rise [46]. Considering that the spread of
alien species is favoured by the globalisation of the circulation of people and
commodities and by the artificialisation of ecosystems [47], it is very unlikely that
the arrival of new exotic species on the Seine River basin will decline, at least for the
next few decades. If the colonisation rate of alien species continues at its current
level (and even more so if it keeps increasing), the number of non-native species
noted in the Seine River basin could quickly exceed the number of native species.
In the 2000s, an established population of Misgurnus anguillicaudatus was
identified in an ornamental pond in Paris (eradicated since then). This weather
loach, native of East Asia, is frequently used as food or aquarium fish and has
been recently detected in several European countries [48]. More recently, in 2016, a
Changes in Fish Communities of the Seine Basin over a Long-Term Perspective
317