132
Analyses of variance (ANOVA) (Saporta, 2006)used to compare bluefin tuna abundances
between seasons. To do this, we asked the question:
Does the abundance of bluefin tuna in the Mediterranean change according to the
season?
RESULTS AND DISCUSSION
1. Statistical analysis
The table below illustrates the descriptive statistical summary of the different environmental
variables in more than 18,000 points along the Algerian coasts and the biological variables,
size and weight of 2601 individuals of bluefin tuna.
Table 1. Summary of descriptive statistics by variable
1.1. Analyse of variance
Table 2. Results of analyses of variance
According to the analysis of variance Table 2, the calculated p-value (0.0002) is below the
significance level alpha=0.05, so we have to reject the null hypothesis H0 and retain the
alternative hypothesis H1, taking a 0.02% risk of being wrong. The effect of the season was
measured using a variance ratio (F = 7.7411) Table 1, the higher this ratio the more significant
the effect of the season. We conclude that there is a significant effect of season on the abundance
of thunnus thynnus in the Mediterranean and particularly along the Algerian coast.
Lt
Wt
Chl a
(mg.m3)
NO3
(mmol.m3)
O2
S (psu)
T
Crrt spd
(m/s)
Ht Vg
(m)
Dist_cot
(degree)
(cm)
(kg)
(mmol.m3)
(°c)
N
22601 22601 21192
21172
21172 19586 19586 19438 18448
22498
max
312.88 474.39
6.59
8.14
329.92
39.52
28.19
0.91
5.23
2.72
Min
39.00
2.00
0.06
0.01
203.29
31.74
9.20
0.00
0.00
0.00
Avr
186.83 133.53
0.19
0.30
237.94
36.86
18.67
0.22
1.08
0.37
Dev-str
52.85
76.72
0.43
0.81
8.97
0.55
1.69
0.14
0.62
0.22
IC 5%.
0.69
1.00
0.01
0.01
0.12
0.01
0.02
0.00
0.01
0.00
m+ic
187.52 134.53
0.19
0.31
238.06
36.87
18.70
0.22
1.09
0.38
m-ic
186.14 132.53
0.18
0.29
237.82
36.85
18.65
0.22
1.07
0.37
CV
0.28
0.58
2.28
2.69
0.04
0.02
0.09
0.64
0.57
0.58
Source
DDL Somme des carrés Moyenne des carrés
F
Pr > F
Modèle
3
10104715,7424
3368238,5808 7,7411
0,0002
Erreur
57
24801249,5035
435109,6404
Total corrigé
60
34905965,2459
Analyses of variance (ANOVA) (Saporta, 2006)used to compare bluefin tuna abundances
between seasons. To do this, we asked the question:
Does the abundance of bluefin tuna in the Mediterranean change according to the
season?
RESULTS AND DISCUSSION
1. Statistical analysis
The table below illustrates the descriptive statistical summary of the different environmental
variables in more than 18,000 points along the Algerian coasts and the biological variables,
size and weight of 2601 individuals of bluefin tuna.
Table 1. Summary of descriptive statistics by variable
1.1. Analyse of variance
Table 2. Results of analyses of variance
According to the analysis of variance Table 2, the calculated p-value (0.0002) is below the
significance level alpha=0.05, so we have to reject the null hypothesis H0 and retain the
alternative hypothesis H1, taking a 0.02% risk of being wrong. The effect of the season was
measured using a variance ratio (F = 7.7411) Table 1, the higher this ratio the more significant
the effect of the season. We conclude that there is a significant effect of season on the abundance
of thunnus thynnus in the Mediterranean and particularly along the Algerian coast.
Lt
Wt
Chl a
(mg.m3)
NO3
(mmol.m3)
O2
S (psu)
T
Crrt spd
(m/s)
Ht Vg
(m)
Dist_cot
(degree)
(cm)
(kg)
(mmol.m3)
(°c)
N
22601 22601 21192
21172
21172 19586 19586 19438 18448
22498
max
312.88 474.39
6.59
8.14
329.92
39.52
28.19
0.91
5.23
2.72
Min
39.00
2.00
0.06
0.01
203.29
31.74
9.20
0.00
0.00
0.00
Avr
186.83 133.53
0.19
0.30
237.94
36.86
18.67
0.22
1.08
0.37
Dev-str
52.85
76.72
0.43
0.81
8.97
0.55
1.69
0.14
0.62
0.22
IC 5%.
0.69
1.00
0.01
0.01
0.12
0.01
0.02
0.00
0.01
0.00
m+ic
187.52 134.53
0.19
0.31
238.06
36.87
18.70
0.22
1.09
0.38
m-ic
186.14 132.53
0.18
0.29
237.82
36.85
18.65
0.22
1.07
0.37
CV
0.28
0.58
2.28
2.69
0.04
0.02
0.09
0.64
0.57
0.58
Source
DDL Somme des carrés Moyenne des carrés
F
Pr > F
Modèle
3
10104715,7424
3368238,5808 7,7411
0,0002
Erreur
57
24801249,5035
435109,6404
Total corrigé
60
34905965,2459