Organohalogen concentrations and a gross and histologic ...

No. skulls collected
50
45
40
35
30
25
20
15
10
5
0
velopmental instability (i.e. the magnitude of FA) could have been initiated
(e.g. Siegel and Doyle 1975a-c, Doyle et al., 1977, Siegel et al., 1977a). The
model was successively reduced for non-significant interactions (p>0.05) and
the significance was evaluted from the remaining reduced model.
2.5.6 FA versus contaminants
For the 94 samples from 1999 to 2002 of which both skulls and contaminant
analysis were available a non-parametric Spearman correlation coefficient
was used to test for significant correlations between levels of individual
organohalogens and FA. Due to the large numbers of tests (k=98) a Bonferroni
correction of the p-estimates was applied to avoid the generation of
significant results simply by chance. The critical alpha level was set to
p=0.05/98=0.0005.
3. Results
3.1 The sample
Before analysing the trend of FA between periods (before and after 1960)
and age/sex groups, individuals were grouped as being adult males (≥6
years), adult females (≥5 years) and the remaining individuals of both sexes
as subadults (Table 2). The sample consisted of a total of 283 individuals
distributed as 142 subadults, 78 adult males and 63 adult females (Table 2).
The number of skulls and age of individuals were equally distributed over
time with few peaks, although the period 2000-2002 was over-represented
(Fig. 2).
92 08 25 28 33 36 60 66 69 73 85 99 02
Year
Table 2
Age, sex and number of polar bear skulls divided on periods. The number of subadults and
females differ in particular between two periods investigated.
Period/group Subadults Females Males Sum
1892-1960 45 13 37 94
1961-2002 97 50 41 189
Sum 142 63 78 283
Figure 2
Number of skulls collected per year from 1892 to 2002 (n=283) (left) and their individual age (right).
Age (years)
30
25
20
15
10
5
0
1880 1900 1920 1940 1960 1980 2000 2020
Year
101