359Underwater photos taken by the Arvernes Diving Club (D
Chassain) show a change in bottom conditions in the breeding
grounds. In the early 1990s, breeding ground bottoms were
free of vegetation and the small amounts of deposits were easy
for spawners to clean. In 2003, a similar dive showed a lake
bottom clogged with stringy algae, making cleaning, incuba-
tion, and hatching uncertain (Fig. 21.15 ). The degradation of
this excess organic matter is probably the reason of the lack of
dissolved oxygen concentration and breeding success.
21.5 Ongoing Studies, Incubators,
Tracking, Monitoring
Several studies and surveys have been implemented and/or
are currently underway as part of the Territorial Contract
framework governing lakes fed by the Couze Pavin river.
Lake Pavin is monitored under Water Framework Directive
following a standardized protocol performed by the ONEMA
(Olivier 2012 ). The most important fi sh-related issue facing
Lake Pavin is the tracking of its Arctic char population and
its evolution. It is for this reason that the protocol we propose
is based primarily on the study of this fi sh.
21.5.1 Tracking the Population by Fishing
Expedition
Three annual fi shing expeditions will be organized—one in
the spring, one in summer, and one in autumn, for 3 years.
Two exploration methods will be implemented:
- Fishing with two batteries of two-meter-wide vertical gill
nets, one 50 m deep, the other 25 m deep. This method is
designed to explore the entire column of oxygenated
water (50 m) and the most productive zone (25 m). Each
battery will use a range of 7 mesh sizes (10 mm, 15 mm,
20 mm, 30 mm, 40 mm, 50 mm, 60 mm), giving a total of
14 vertical nets. These nets will always be set in the same
place from expedition to expedition. The advantages of
this method are that it limits catches and situates fi sh at
specifi c depths, as the side ropes are depth-graduated.- Fishing by horizontal nets, called “spiders”. For each
excursion, we will set four horizontal nets extending from
25 to 6 m (spider type) with mesh sizes of 16 mm, 22 mm,
and 32 mm in order to target different age-groups and
obtain individuals in a range of sizes from 12 cm to 40 cm.
The ‘spiders’ will be placed specifi cally to target char. The
nets will be positioned at depths of between 8 and 25 m in
the zones most frequented by char. Their positioning will
remain identical from expedition to expedition.
The following protocol will be implemented for all nets
and fi sh:- The location of each net will be determined using GPS
and depth of laying area determined by echo sounding. - Each fi sh will be recorded (including, for vertical nets,
depth at which it was caught), individually measured and
weighed, and scale samples will be taken from the stan-
dardized area for each species. - Tagged fi sh will be identifi ed (by type of tag), weighed,
and measured. - Live fi sh will be released back into the lake. Dead fi sh
will be made available to the owner of the lake.
The fi rst year of fi shing is not designed to capture tagged
fi sh and will serve as calibration in order to optimize catches
(Rivier 1996 ).21.5.2 Marking CharIn December, fl ash (2-h) catches of char will be performed
by the FDPPMA 63. The captured spawners will be stocked
at the local salmon farm at Besse in quarantine. Reproduction
will be carried out at the salmon farm. The fry produced will
be raised until August or September, then released into
Pavin. For this protocol, we propose to tag fi sh before release
with a distinctive year-specifi c tag for the years 2014–2016.- Every individual fi sh will be tagged before being released
into the lake. - When catches are made for population tracking, number
of tagged individuals and type of tag will be recorded. - This tagging and tracking by gill net catch will allow us to
determine, via statistical analysis, the number of Arctic
char resulting from releases versus the number from natu-
ral reproduction in situ.
Fig. 21.15 Sub-aquatic view of a spawning area of S. alpinus
21 History of the Fish Fauna of Lake Pavin: A Population Heavily Infl uenced by Man?