The success of an introduction operation can be measured by the increase of the number of places where the animal is settled. The graph on the right shows the number of new sites occupated by year and the cumulated number of sites. After a stage of acclimatization which extended up to 1990, it was noted that each year new sites were observed.

The representation of the cumulative total shows a regular increasing, leading to 148 referenced sites at the end of 2020 .

Descriptive Statistics of site number increasing

Period

Total Nb Sites

Mediane by year

Mean by year

Theoretic Number

increasing rate

Doubling Time

Before 1989

16

1

1.6 ± 2.08

10

1.5

0.46

From 1990 to 1999

28

3

2.8 ± 2.04

30

0.18

3.85

From 2000 to 2009

68

6

6.8 ± 5.66

60

0.15

4.62

Since 2010

36

4.5

4.5 ± 3.21

36

0.04

17.33

2010 Forecasts

50

xxx

45

0.114

6.08

2020 Forecasts

70

xxx

65

0.074

9.36

Total Number of Sites : it represents the total number of new sites observed during the related period. Median by year : it represents the median number m of new sites observed by year during the related period. Mean by year : it represents the mean number of new sites by year for the related period. Mean is completed by ± the standard-error. Theoretic Number : it represents the theoretic number of new sites for the period, calculated by multiplying the median m by the number of years n : NT = m * n Increasing Rate : the increasing rate by period is calculated by substracting the number of sites S(t) of the starting year from the number of the last year S(t+n). The increase [S(t+n) - S(t)] is related to the whole number of known sites during the periode S(t) * n (with n = number of yearss) : TA = [S(t+n) - S(t)] / S(t) * n Doubling Time: is the number of years necessary to have twice more sites, in an hypothesis of linear increase. It is approximated by the formula TD = ln(2) / TA.