136
seasonally varying physical and chemical factors. Among these factors we were interested in
the following: Temperature, Salinity, Current speed, Wave height, Chlorophyll a, Dissolved
oxygen and Nitrate.
2.1.Physical factors
Temperature and salinity are the main hydrological factors describing water masses in a marine
environment (Aminot and Kérouel, 2004b). The important variations of the two factors are in
function of the seasonal cycle, moreover fig.6, represents well this variation with the wire of
the seasons, we noted a resemblance between the two curves, of temperature and salinity, the
increase of the temperature followed by an increase of the salinity, in the same way in the
opposite case. In the summer season, the temperatures are obviously very high (on average
between 21.5 and 25.8°C), as is the salinity (on average between 36 and 39 psu).
Fig. 6. Seasonal variation of physical factors: temperature and salinity.
In the winter season, the water masses cool down due to the effect of lower temperatures (on
average 12.8 to 16°c), also for the salinity drops on average from 35.4 to 37 psu. According to
Freon and Misund (Fréon and Misund, 1999b), the distribution of bluefin tuna depends on the
environmental temperature, which averages 10-28°C. In Atlantic bluefin tuna farms, the
temperature should be in the range of 18-26°C (Caill-Milly et al., 2002b). Bluefin tuna have
been fished in surface waters of great variation in temperature and salinity Table 2, they can
Fig. 7. Seasonal variations in bluefin tuna abundances and mean lengths in relation to
environmental factors, temperature.
11,00
13,00
15,00
17,00
19,00
21,00
23,00
25,00
27,00
35,00
36,00
37,00
38,00
39,00
40,00
2000-Tr2 2000-Tr2_w
2000-Tr3 2001-Tr2 2001-Tr2_w
2001-Tr3 2002-Tr2 2002-Tr2_w
2002-Tr3 2003-Tr2 2003-Tr2_w 2003Tr3
2004-Tr2 2004-Tr2_w
2004-Tr3 2004-Tr4 2005-Tr1
2005-Tr2 2005-Tr3 2005-Tr4 2006-Tr2 2006-Tr3 2006-Tr4 2007-Tr1 2007-Tr2 2007-Tr2_w
2007-Tr3 2007-Tr4 2008-Tr2 2008-Tr3
2009-Tr2 2009-Tr3 2010-Tr3 2011-Tr2 2011-Tr3 2011-Tr4 2012-Tr1 2012-Tr2 2012-Tr3 2012-Tr4 2013-Tr1 2013-Tr2 2013-Tr3
2013-Tr4 2014-Tr1 2014-Tr2 2014-Tr3 2014-Tr4 2015-Tr1 2015-Tr2 2015-Tr3 2015-Tr4 2016-Tr1 2016-Tr2 2016-Tr3 2016-Tr4 2017-Tr1 2017-Tr2 2017-Tr3 2017-Tr4 2018-Tr1 2018-Tr2 2018-Tr3 2018-Tr4 2019-Tr1 2019-Tr2 2019-Tr3
T
(c°)
S
(psu)
Time (trimester)
S (psu)
T (°c)
237,07 230,66 227,82 215,00 225,98 237,50 233,84 231,24 233,75 225,28 255,15 230,60 205,00 142,60 221,31 251,33 187,00
223,65 223,62 296,43 221,25 244,38 231,67 181,06 163,78 159,95 185,54 229,00
226,09 146,95 220,28 170,96 155,86 179,34 254,56
181,67 221,27 233,19
237,50
227,53 257,50 171,55
256,00 226,00 224,48 226,55 219,85 227,12
218,76 247,50 205,00 225,79 230,83 227,50 245,00 260,24 258,00 228,00 218,67 169,25 162,50
11,00
13,00
15,00
17,00
19,00
21,00
23,00
25,00
27,00
0
500
1000
1500
2000
2500
3000
3500
2018-Tr3 2012-Tr3 2015-Tr3 2000-Tr3 2017-Tr3 2007-Tr3 2014-Tr3 2016-Tr3 2004-Tr3 2006-Tr3 2011-Tr3 2007-Tr4 2002-Tr3 2005-Tr2 2013-Tr2 2010-Tr3 2018-Tr4
2017-Tr4 2016-Tr4 2006-Tr4 2014-Tr4 2013-Tr3 2009-Tr3 2014-Tr2 2007-Tr2 2006-Tr2 2000-Tr2 2012-Tr4 2001-Tr2_w
2011-Tr4 2009-Tr2 2015-Tr2 2002-Tr2 2008-Tr2 2003-Tr2 2005-Tr4
2000-Tr2_w
2001-Tr2 2015-Tr4 2013-Tr4 2002-Tr2_w
2011-Tr2 2003-Tr2_w
2012-Tr2 2004-Tr4 2004-Tr2 2007-Tr2_w 2004-Tr2_w
2005-Tr1 2007-Tr1 2018-Tr2 2016-Tr2 2018-Tr1 2017-Tr2
2017-Tr1 2013-Tr1 2015-Tr1 2016-Tr1 2014-Tr1 2012-Tr1 2008-Tr3 2005-Tr3
2003Tr3 2001-Tr3 2019-Tr2 2019-Tr3 2019-Tr1
Lt (cm)
T
(°c)
Abundance
Time ( trimester)
Headcount (ni)
T (°c)
seasonally varying physical and chemical factors. Among these factors we were interested in
the following: Temperature, Salinity, Current speed, Wave height, Chlorophyll a, Dissolved
oxygen and Nitrate.
2.1.Physical factors
Temperature and salinity are the main hydrological factors describing water masses in a marine
environment (Aminot and Kérouel, 2004b). The important variations of the two factors are in
function of the seasonal cycle, moreover fig.6, represents well this variation with the wire of
the seasons, we noted a resemblance between the two curves, of temperature and salinity, the
increase of the temperature followed by an increase of the salinity, in the same way in the
opposite case. In the summer season, the temperatures are obviously very high (on average
between 21.5 and 25.8°C), as is the salinity (on average between 36 and 39 psu).
Fig. 6. Seasonal variation of physical factors: temperature and salinity.
In the winter season, the water masses cool down due to the effect of lower temperatures (on
average 12.8 to 16°c), also for the salinity drops on average from 35.4 to 37 psu. According to
Freon and Misund (Fréon and Misund, 1999b), the distribution of bluefin tuna depends on the
environmental temperature, which averages 10-28°C. In Atlantic bluefin tuna farms, the
temperature should be in the range of 18-26°C (Caill-Milly et al., 2002b). Bluefin tuna have
been fished in surface waters of great variation in temperature and salinity Table 2, they can
Fig. 7. Seasonal variations in bluefin tuna abundances and mean lengths in relation to
environmental factors, temperature.
11,00
13,00
15,00
17,00
19,00
21,00
23,00
25,00
27,00
35,00
36,00
37,00
38,00
39,00
40,00
2000-Tr2 2000-Tr2_w
2000-Tr3 2001-Tr2 2001-Tr2_w
2001-Tr3 2002-Tr2 2002-Tr2_w
2002-Tr3 2003-Tr2 2003-Tr2_w 2003Tr3
2004-Tr2 2004-Tr2_w
2004-Tr3 2004-Tr4 2005-Tr1
2005-Tr2 2005-Tr3 2005-Tr4 2006-Tr2 2006-Tr3 2006-Tr4 2007-Tr1 2007-Tr2 2007-Tr2_w
2007-Tr3 2007-Tr4 2008-Tr2 2008-Tr3
2009-Tr2 2009-Tr3 2010-Tr3 2011-Tr2 2011-Tr3 2011-Tr4 2012-Tr1 2012-Tr2 2012-Tr3 2012-Tr4 2013-Tr1 2013-Tr2 2013-Tr3
2013-Tr4 2014-Tr1 2014-Tr2 2014-Tr3 2014-Tr4 2015-Tr1 2015-Tr2 2015-Tr3 2015-Tr4 2016-Tr1 2016-Tr2 2016-Tr3 2016-Tr4 2017-Tr1 2017-Tr2 2017-Tr3 2017-Tr4 2018-Tr1 2018-Tr2 2018-Tr3 2018-Tr4 2019-Tr1 2019-Tr2 2019-Tr3
T
(c°)
S
(psu)
Time (trimester)
S (psu)
T (°c)
237,07 230,66 227,82 215,00 225,98 237,50 233,84 231,24 233,75 225,28 255,15 230,60 205,00 142,60 221,31 251,33 187,00
223,65 223,62 296,43 221,25 244,38 231,67 181,06 163,78 159,95 185,54 229,00
226,09 146,95 220,28 170,96 155,86 179,34 254,56
181,67 221,27 233,19
237,50
227,53 257,50 171,55
256,00 226,00 224,48 226,55 219,85 227,12
218,76 247,50 205,00 225,79 230,83 227,50 245,00 260,24 258,00 228,00 218,67 169,25 162,50
11,00
13,00
15,00
17,00
19,00
21,00
23,00
25,00
27,00
0
500
1000
1500
2000
2500
3000
3500
2018-Tr3 2012-Tr3 2015-Tr3 2000-Tr3 2017-Tr3 2007-Tr3 2014-Tr3 2016-Tr3 2004-Tr3 2006-Tr3 2011-Tr3 2007-Tr4 2002-Tr3 2005-Tr2 2013-Tr2 2010-Tr3 2018-Tr4
2017-Tr4 2016-Tr4 2006-Tr4 2014-Tr4 2013-Tr3 2009-Tr3 2014-Tr2 2007-Tr2 2006-Tr2 2000-Tr2 2012-Tr4 2001-Tr2_w
2011-Tr4 2009-Tr2 2015-Tr2 2002-Tr2 2008-Tr2 2003-Tr2 2005-Tr4
2000-Tr2_w
2001-Tr2 2015-Tr4 2013-Tr4 2002-Tr2_w
2011-Tr2 2003-Tr2_w
2012-Tr2 2004-Tr4 2004-Tr2 2007-Tr2_w 2004-Tr2_w
2005-Tr1 2007-Tr1 2018-Tr2 2016-Tr2 2018-Tr1 2017-Tr2
2017-Tr1 2013-Tr1 2015-Tr1 2016-Tr1 2014-Tr1 2012-Tr1 2008-Tr3 2005-Tr3
2003Tr3 2001-Tr3 2019-Tr2 2019-Tr3 2019-Tr1
Lt (cm)
T
(°c)
Abundance
Time ( trimester)
Headcount (ni)
T (°c)