137
withstand low water temperatures of 9.2°c and as well as having the ability to live in warm
waters, up to 28.19°c. (Block et al ., 2001) cited: tagging and tracking data from the archives
testified that the BFT can withstand cold (up to 3°C) as well as warm temperatures (up to 30°C)
and it maintains a stable internal body temperature. The temperature in the spring season warms
the marine water masses. These not very warm water masses (average temperature varies
between 17 and 19.5°C) mark the presence of an overabundance of bluefin tuna (average total
length from 146 to 181 cm), Fig.7. In addition to this, large individuals averaging 250 cm, they
may frequent warmer waters (average temperature of 22°C) in the summer period. And the
largest catches are recorded in areas with a temperature of between 17 and 20°C.
These are in agreement with the observations of Lozano Cabo (1958) and Tiews K. (1963).
They noted that the best catches of bluefin tuna from the Moroccan and Spanish traps were
taken in areas with surface temperatures between 19.25 and 20.5 °C. According to (Ottersen
Geir et al(Ottersen et al., 2004b) the temperature factor can influence the spawning periods.
The spawning period of bluefin tuna in the Mediterranean Sea is June-July (Mylonas et al.,
2007b) ; (MacKenzie and Mariani, 2012b) ; Collette and Nauen, 1983 and (Cort, 1990b).
Indeed, low temperatures slow down spawning because of the slow development of the gonads.
Whereas high temperatures allow earlier spawning because of the rapid development of the
gonads. The surface waters of fishing areas with high bluefin tuna productivity are characterised
by stable salinity levels, which vary on average from 36.6 to 37.1 psu and from 37.8 to 37.9 psu
in spring and summer respectively Fig.8. Bluefin tuna have demanding requirements, mainly
for stable salinity and well oxygenated water (Caill-Milly et al., 2002b). Furthermore, there is
a relationship between the total length of the species studied and the current speed.
Fig. 8. Seasonal variations in bluefin tuna abundances and mean lengths in relation to
environmental factors, salinity.
33,00
34,00
35,00
36,00
37,00
38,00
39,00
40,00
230,60 254,56 296,43 230,66 237,50 221,31 251,33 223,65 231,24 237,07 244,38 224,48 255,15 227,82 225,79 227,53 205,00 225,28 181,06 237,50 187,00 226,09 142,60 205,00 247,50 221,27 227,12 227,50 220,28 225,98 229,00 159,95 155,86 218,76 221,25 233,84
171,55 146,95 223,62
181,67 163,78 179,34
170,96
185,54 219,85 215,00 257,50 226,00 256,00 231,67 233,19 233,75 230,83 226,55 245,00 260,24 258,00 228,00 218,67 169,25 162,50
0
500
1000
1500
2000
2500
3000
3500
2007-Tr4 2005-Tr4 2006-Tr4 2012-Tr3 2007-Tr3 2013-Tr2 2010-Tr3 2017-Tr4 2016-Tr3 2018-Tr3 2013-Tr3 2018-Tr2 2011-Tr3 2015-Tr3 2016-Tr1 2012-Tr2 2002-Tr3 2006-Tr3 2014-Tr2 2011-Tr2 2018-Tr4 2011-Tr4 2005-Tr2 2015-Tr1 2013-Tr1 2015-Tr4 2017-Tr2 2012-Tr1 2015-Tr2 2017-Tr3 2012-Tr4 2006-Tr2 2008-Tr2 2017-Tr1 2014-Tr4 2014-Tr3
2004-Tr2_w 2004-Tr2 2009-Tr2 2016-Tr4
2001-Tr2_w 2001-Tr2 2007-Tr2 2003-Tr2
2003-Tr2_w 2000-Tr2_w 2002-Tr2_w 2002-Tr2
2007-Tr2_w 2000-Tr2 2018-Tr1 2000-Tr3 2004-Tr4 2007-Tr1 2005-Tr1 2009-Tr3 2013-Tr4 2004-Tr3 2014-Tr1 2016-Tr2 2008-Tr3 2005-Tr3 2003Tr3
2001-Tr3 2019-Tr2 2019-Tr3 2019-Tr1
S
(psu)
Lt (cm)
Abundance
Time (trimester)
Abundance
S (psu)
withstand low water temperatures of 9.2°c and as well as having the ability to live in warm
waters, up to 28.19°c. (Block et al ., 2001) cited: tagging and tracking data from the archives
testified that the BFT can withstand cold (up to 3°C) as well as warm temperatures (up to 30°C)
and it maintains a stable internal body temperature. The temperature in the spring season warms
the marine water masses. These not very warm water masses (average temperature varies
between 17 and 19.5°C) mark the presence of an overabundance of bluefin tuna (average total
length from 146 to 181 cm), Fig.7. In addition to this, large individuals averaging 250 cm, they
may frequent warmer waters (average temperature of 22°C) in the summer period. And the
largest catches are recorded in areas with a temperature of between 17 and 20°C.
These are in agreement with the observations of Lozano Cabo (1958) and Tiews K. (1963).
They noted that the best catches of bluefin tuna from the Moroccan and Spanish traps were
taken in areas with surface temperatures between 19.25 and 20.5 °C. According to (Ottersen
Geir et al(Ottersen et al., 2004b) the temperature factor can influence the spawning periods.
The spawning period of bluefin tuna in the Mediterranean Sea is June-July (Mylonas et al.,
2007b) ; (MacKenzie and Mariani, 2012b) ; Collette and Nauen, 1983 and (Cort, 1990b).
Indeed, low temperatures slow down spawning because of the slow development of the gonads.
Whereas high temperatures allow earlier spawning because of the rapid development of the
gonads. The surface waters of fishing areas with high bluefin tuna productivity are characterised
by stable salinity levels, which vary on average from 36.6 to 37.1 psu and from 37.8 to 37.9 psu
in spring and summer respectively Fig.8. Bluefin tuna have demanding requirements, mainly
for stable salinity and well oxygenated water (Caill-Milly et al., 2002b). Furthermore, there is
a relationship between the total length of the species studied and the current speed.
Fig. 8. Seasonal variations in bluefin tuna abundances and mean lengths in relation to
environmental factors, salinity.
33,00
34,00
35,00
36,00
37,00
38,00
39,00
40,00
230,60 254,56 296,43 230,66 237,50 221,31 251,33 223,65 231,24 237,07 244,38 224,48 255,15 227,82 225,79 227,53 205,00 225,28 181,06 237,50 187,00 226,09 142,60 205,00 247,50 221,27 227,12 227,50 220,28 225,98 229,00 159,95 155,86 218,76 221,25 233,84
171,55 146,95 223,62
181,67 163,78 179,34
170,96
185,54 219,85 215,00 257,50 226,00 256,00 231,67 233,19 233,75 230,83 226,55 245,00 260,24 258,00 228,00 218,67 169,25 162,50
0
500
1000
1500
2000
2500
3000
3500
2007-Tr4 2005-Tr4 2006-Tr4 2012-Tr3 2007-Tr3 2013-Tr2 2010-Tr3 2017-Tr4 2016-Tr3 2018-Tr3 2013-Tr3 2018-Tr2 2011-Tr3 2015-Tr3 2016-Tr1 2012-Tr2 2002-Tr3 2006-Tr3 2014-Tr2 2011-Tr2 2018-Tr4 2011-Tr4 2005-Tr2 2015-Tr1 2013-Tr1 2015-Tr4 2017-Tr2 2012-Tr1 2015-Tr2 2017-Tr3 2012-Tr4 2006-Tr2 2008-Tr2 2017-Tr1 2014-Tr4 2014-Tr3
2004-Tr2_w 2004-Tr2 2009-Tr2 2016-Tr4
2001-Tr2_w 2001-Tr2 2007-Tr2 2003-Tr2
2003-Tr2_w 2000-Tr2_w 2002-Tr2_w 2002-Tr2
2007-Tr2_w 2000-Tr2 2018-Tr1 2000-Tr3 2004-Tr4 2007-Tr1 2005-Tr1 2009-Tr3 2013-Tr4 2004-Tr3 2014-Tr1 2016-Tr2 2008-Tr3 2005-Tr3 2003Tr3
2001-Tr3 2019-Tr2 2019-Tr3 2019-Tr1
S
(psu)
Lt (cm)
Abundance
Time (trimester)
Abundance
S (psu)