350
21.3.2.3 Evolution of the List of Species Present
Over Time
Review of the literature emerges four separate periods in
which a list of species present in the lake was established
more or less objectively (Table 21.1 ):
In 1939, L. Olivier does not specify what methods were
used for sampling.
For tracking carried out by the FDPPMA 63, (i) the high
selectivity in the nets used in conjunction with the specifi c
targeting of Arctic char had the effect of inducing a sampling
bias, and (ii) littoral areas were not sampled, with only visual
observations used to complete the list (italics).
For WFD NF EN 14757 (AFNOR 2005 ) sampling, the
protocol is standardized but does not cater to sampling litto-
ral areas of the lake; visual observations are not referenced.
In comparison to the list compiled by Olivier ( 1939 ), the
big charges are the disappearance of stickleback, reported as
an original species, and the disappearance of crayfi sh,
reported as having been introduced in 1859. Over the past 20
years, allowing for the fact that the samplings are not compa-
rable, the species list has essentially changed little. Note the
absence of catches of brown trout and minnows with the
WFD protocol whereas anglers report regularly catching or
observing these species.
The standout feature is the appearance of many intro-
duced species:
- voluntarily by managers. Perch were introduced in the
1950s by a lake farmer. Rainbow trout ( Oncorhynchus
mykiss ) were introduced 1997, with individuals sourced
from Lake Bouillouses (Pyrénées-Orientales). This spe-
cies is largely maintained by yearly releases. For 10 years,
every individual released was tagged, but some untagged
fi sh were caught between 1997 and 2005, which in con-
junction with the observation of reproductive activity on
the bank leads us to believe that a small part of the popu-
lation is the product of reproduction in situ.- by anglers, tourists, children, etc. using the lake for recre-
ational purposes. Crucian carp, rudd, chub, and roach
were introduced in this way. Many of these cyprinids
were probably used as live bait for fi shing and dumped in
the lake when no longer needed. Regarding roach, note
that Olivier ( 1939 ) reports its introduction in 1859 as a
failure. Do the individuals caught come from recent
releases or have they managed to persist in the lake’s
waters since that date? Note too that anglers recently
reported taking ides ( Leusciscus idus ). These fi sh are nat-
urally present in the northern watershed of the Loire and
are often sold as livebait by fi shing tackle shops. These
catches would appear to confi rm the hypothesis related to
the practice of dumping livebait (despite regulations in
place prohibiting its use).
The presence of tench and gudgeon also raises questions.
If gudgeon have visibly persisted since the inventories taken
by Olivier ( 1939 ) and perhaps even since the original fi sh
fauna, tench were reported in 1939 as a failed attempt at
introduction, then is the capture of two individuals in the
space of 30 years to be ascribed to recent introductions or to
the persistence of individuals released in 1859?21.3.2.4 Evolution of Numerical Abundance
We compiled all the data obtained by the FDPPMA 63 over
an 11-year period and compared the numbers against the
relative proportions of these species in studies performed for
WFD monitoring in 2005 and again in 2012 (Fig. 21.3 ).
Despite the different sampling protocols, just two species
dominate the fi sh population, i.e. Arctic char and perch,
although their order of abundance is reversed between sam-
pling methods. Species such as rainbow trout have remained
stable in terms of representation while chub, rudd and roach050000010000001500000200000025000001995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005UEPYearsFig. 21.2 Annual evolution of Units of
Fishing Effort
F. D e s m o l l e s