THE TUNA FISHERY ALONG THE ANGOLAN COAST

SCRS/2012/037
Collect. Vol. Sci. Pap. ICCAT, 69(5): 2033-2036 (2013) THE TUNA FISHERY ALONG THE ANGOLAN COAST
K. Kilongo, V. Jonico and H. Nsilulu
SUMMARY
The abundance and distribution of tuna, as other marine resources along the Angolan coast,
are highly influenced by the presence of the warm water current of Angola in the north area
and the cold water current of Benguela in the south area, creating the Angola-Benguela Front
with the seasonal shift between 14º-16ºS. The wide specific biodiversity found in the southern
area is associated to the favorable distribution influenced by the cold waters, very rich in
nutrients. The most common species found along this coast are Sarda sarda (Atlantic bonito),
Euthynnus alletteratus (little tunny), Auxis thazard (frigate tuna), Scomberomorus tritor (West
African Spanish mackerel, Katsuwonus pelamis (skipjack tuna), Thunnnus albacares (yellowfin
tuna), Thunnus obesus (bigeye tuna) and Thunnus alalunga (albacore). The high concentrations
are related to a define period of the year, mainly more abundant between June and December,
that is the period that the catches are very important and licenses are given.
RÉSUMÉ
L'abondance et la répartition des thonidés, tout comme les autres ressources marines
rencontrées sur la côte angolaise, sont fortement influencées par la présence du courant d'eau
tempérée dans la zone septentrionale de l'Angola et du courant d'eau froide du Benguela dans
la zone méridionale, ce qui crée le Front Angola-Benguela avec le déplacement saisonnier
entre 14º-16ºS. La vaste biodiversité spécifique rencontrée dans la zone méridionale est
associée à la distribution favorable influencée par les eaux froides, très riches en nutriments.
Les espèces les plus communément trouvées le long de cette côte sont la bonite à dos rayé de
l’Atlantique (Sarda sarda), la thonine commune (Euthynnus alletteratus), l'auxide (Auxis
thazard), le thazard blanc (Scomberomorus tritor), le listao (Katsuwonus pelamis), l'albacore
(Thunnus albacares), le thon obèse (Thunnus obesus) et le germon (Thunnus alalunga). Les
fortes concentrations sont associées à une période de l'année bien définie et sont
essentiellement plus abondantes entre juin et décembre ; il s'agit de la période où les captures
sont très importantes et les licences sont octroyées.
RESUMEN
La abundancia y distribución de túnidos, al igual que las de otros recursos marinos a lo largo
de la costa de Angola, están bajo la fuerte influencia de la corriente de aguas cálidas de
Angola en la zona septentrional y de la corriente de aguas frías de Benguela en la zona
meridional, que crean el frente Angola-Benguela con un desplazamiento estacional entre 14º16º S. La biodiversidad específica amplia de la zona meridional está asociada con la
distribución favorable bajo la influencia de las aguas frías, muy ricas en nutrientes. Las
especies más comunes de estas costas son Sarda sarda (bonito del Atlántico), Euthynnus
alletteratus (bacoreta), Auxis thazard (melva), Scomberomorus tritor (carita oeste africano),
Katsuwonus pelamis (listado), Thunnus albacares (rabil), Thunnus obesus (patudo) y Thunnus
alalunga (atún blanco). Las elevadas concentraciones están relacionadas con un periodo
definido del año, más abundantes entre junio y diciembre, que es el periodo en el que las
capturas son muy importantes y para el que se conceden licencias.
KEYWORDS
Tuna abundance, distribution, tuna concentration
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1. Fishery
Big tuna are industrially fished by the joint-venture companies with the flag of the vessel owner country. During
the last few years, licenses are given to the Japanese, Spanish and French vessels; the catches are landed abroad
and directly reported to ICCAT. The main species registered in the country, caught as by-catch in the industrial,
semi-industrial and artisanal fisheries are Sarda sarda, Euthynnus alletteratus, Auxis thazard and
Scomberomorus tritor. Other species are simply reported as tuna. Actually, these species are caught as target in
the south of Baía-Farta, located in the south of Benguela, using the trap as gear.
2. Catches
Figure 1 shows the catches of tuna caught as by-catch by the industrial, semi-industrial and artisanal fisheries
from 2005 to 2010. The catches have increased in 2010 due to the improvement registered in the data collection
system by the National Direction of Fisheries of the Ministry of Agriculture, Rural Development and Fisheries.
All the registered species have reached 1500 tons during this year.
Figure 2 shows the catches of tuna caught in Benguela by the artisanal and semi-industrial fisheries, monitored
by the Fisheries Research Centre of Benguela. Tuna are targeted with traps and caught in a very small proportion
by the purse-seiners (Figure 3). 78% of tuna is caught by traps, 20% by the purse-seiners and 2% by gillnet. In
general, the catches show a decreasing trend from 2007 to 2011.
3. Biological sampling
Figures 4 and 5 show the length frequencies distribution by year and mean length by year and month of E.
alletteratus and A. thazard sampled in Benguela. The size of E. alletteratus ranged between 23-74 cm and the
mode between 38-53 cm. The lower mean length was registered in 2009 and 2011 (47) and fluctuates throughout
the months. The size of A. thazard ranged between 20-46 cm and the mode showed a wide range of variability
between the years. The lower mean length was registered in 2008, 2009 and 2011 (34 cm), principally in March,
April and May.
4. Assessment
The National Institute of Fisheries of Angola is improving the quality of data collected in order to be forward to
ICCAT and assessed according to ICCAT methodology.
4000
3500
Catch (ton)
3000
2500
2000
1500
1000
500
0
2005
2006
2007
2008
2009
2010
Year
Tuna
E. alletteratus
S. tritor
S. sarda
Figure 1. Catches of tuna caught as by-catch by the industrial, semi-industrial and artisanal fisheries.
2034
400
350
Catch (ton)
300
250
200
150
100
50
0
2006
2007
2008
2009
2010
2011
Year
A. Thazard
E. alletteratus
S. sarda
Figure 2. Catches of tuna caught in Benguela by the artisanal and semi-industrial fisheries.
100
80
%
60
40
20
0
Trap
Purse seine
Figure 3. Proportion of tuna by gear in Benguela.
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Gilnet
350
250
Mean Lt(cm)
Nº individuals
300
200
150
100
50
0
74
71
68
65
62
59
56
53
50
47
44
41
38
35
32
29
26
23
Year
2007
2008
50
49
48
47
46
45
44
43
42
41
40
0
2009
2010
1
2
3
4
5
2011
6
7
Month
8
9
10
11
12
50
Mean Lt(cm)
49
48
47
46
45
2006
2007
2008
2009
Year
2010
2011
2012
Figure 4. Length frequencies distribution by year and mean length by year and month of E. alletteratus.
300
200
150
Lt(cm)
Nº individuals
250
100
50
0
46
44
42
40
38
36
34
32
30
28
26
24
22
20
Lt(cm)
2007
2008
2009
40
38
36
34
32
30
28
26
24
22
20
0
2010
2011
1
2
3
4
5
6
7
Month
8
9
10
11
12
38
37
Lt(cm)
36
35
34
33
32
31
30
2006
2007
2008
2009
Year
2010
2011
2012
Figure 5. Length frequencies distribution by year and mean length by year and month of A. thazard.
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