Lake Pavin History, geology, biogeochemistry, and sedimentology of a deep meromictic maar lake

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not compare the relationship between number of fi sh released
and number caught without estimating the theoretical sur-
vival rate of released individuals. We estimated the survival
rate of individuals at various stages of development following
the Geiger mortality reference curves ( 1964 ) framed accord-
ing to two mortality hypotheses (Rubin and Buttiker 1993 ).
As 1 + fry were also released, we elected to transform all the
released fry into 1 + equivalents in May (Fig. 21.10 ).
As these values were relatively similar, we chose to use an
average value for the remainder of the study. Comparison of the
average value of the 1 + equivalent number against the number
of fi sh caught 2 years later (3 + ) showed a relationship between
fi sh stocking efforts and number of fi sh caught (Fig. 21.11 ).
Applying a year-on-year mortality rate of 50 %, in line
with much of the literature (Maisse and Baglinière 1991 ;
Richard 1998 ), we created a matrix of annual fi sh catchable.

There was a very good match between the CPUE and esti-

mated adult stock (r = 0.84 n = 8) (Figs. 21.12 , and 21.13 )

which refl ects a strong correlation between CPUE and num-

ber of fi sh released, thus confi rming our hypothesis of a

sharp decline in char reproduction in situ.

21.4.2.4 Tagging

These values suggest that if the infl uence of stocking is so

strong, it is because the number of char produced from natu-

ral reproduction is so low. In order to estimate the number of

fi sh from the lake and the number of fi sh from stocking, we

tagged the char released into the lake. This allowed us to

model the total number of these cohorts at the time tagged

individuals were released into the water, via the Lincoln

Index method according to the Peterson formula (Ricker

1971 ; Rubin and Buttiker 1993 ; Zanella 2003 ). Due to a

0

5000

10000

15000

20000

25000

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Fig. 21.10 Comparisons of upper ( blue ) and
lower ( red ) estimates in 1 + equivalents

12

10

8

6

4

2

0

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

CPUE*1000

Fig. 21.9 Evolution of S. alpinus CPUE
(*1000) from 1995 to 2005

F. D e s m o l l e s

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