35521.4.2.1 Tracking of Catches by Anglers
Anglers on the lake were required to keep a catch log, which
they systematically fi lled out during the fi rst few years of the
initiative. This catch log initiative enabled us to:
- Estimate the total number of fi sh caught in the lake, all
species included - Estimate of size of structures
- Track tagging efforts
However, soon enough, with a lack of verifi cation and the
reluctance of the anglers, the catch books became less infor-
mative, and now 20 years after they were fi rst introduced,
logs and records are no longer kept. However, during the
early years of the catch log initiative, monitoring on these
records allowed us to estimate the number of char caught by
anglers. Knowing the total number of fi shermen and the
number of fi shermen who fi lled out their catch log, we con-
sidered that the fi shing pressure and catch effi ciency of those
having fi lled out their logs was the same for all fi shers. This
allowed us to calculate that between 1997 and 2000, when at
least 10 % of fi shermen reported their catches, anglers caught
between 3000 and 3500 Arctic char per fi shing season.
Catches were concentrated in May, June, and October.
During the hottest months of the year, when the thermocline
forms, the char stay deeper and more diffi cult to catch.
We have had no way of monitoring catches during the last
few years, but given that fi shermen are limited by daily catch
quotas and the number of fi shermen continues to decline, it
is very likely that the catch pressure exerted by fi shermen has
followed the same trend.
21.4.2.2 Tracking of Catches Made Using
Fishing Nets
The lake manager was also required to declare his catches by
fi lling out a capture fi le. The manager caught between 2500
and 3500 char in the period between 1995 and 2005, for an
annual biomass of between 400 and 500 kg (Fig. 21.8 ).
Despite the negative evolution of fi sh stock in recent years,
the manager maintained his catch levels by signifi cantly
increasing his fi shing efforts (Fig. 21.2 ).
Variations between the number of fi sh caught and their
weight are linked to modifi cations in the mesh size of the
fi shnets used (increasing or decreasing the catch size), and to
the accuracy of the fi sh farmer’s declarations.21.4.2.3 Evolution of Catch Per Unit Effort
(CPUE)
As stated above, CPUE was tracked from 1995 to 2005 (Fig.
21.9 ). After this date, the farmer and the owner of the lake
were no longer willing to continue the work following the
necessary methodology, and the data produced became unre-
liable and so has not been included here.
Starting in 1995, commercial fi shing restrictions and
stocking efforts quickly bore fruit, with a signifi cant increase
in the number of captures, peaking in 1998. After 1996, for
economic reasons, the owner wanted to reduce the number of
juveniles released, and catch numbers plummeted while the
farmer increased his fi shing efforts to meet his allowed quota
of char. Thereafter, despite constant efforts to release fry into
Lake Pavin and the establishment of catch quotas, the CPUE
values have continued to fall, which prompts us to believe
that the proportion of Arctic char produced by the Lake con-
tinues to decline.
We consequently implemented tracking on the proportion
of char released into the lake compared to the number pro-
duced by the natural reproduction cycle of Lake Pavin (Rubin
and Buttiker 1993 : Champigneulle et al 2001 ; Zanella 2003 ).
This could only be accomplish if all fry released into the lake
were at a similar growth stage. Despite our requests, and for
various reasons, the fry were released at different stages from
May to September each year. This constraint means we can-600000500000400000300000200000100000040003500
3000
25002000
1500
1000
5000
1995 1996 1997 1998
Obl number Total Obl weight (g)Number Weight (g)1999 2000 2001 2002 2003 2004 2005Fig. 21.8 Annual evolution of catches in
biomass and numbers
21 History of the Fish Fauna of Lake Pavin: A Population Heavily Infl uenced by Man?