Atlantic bluefin tuna (Thunnus thynnus) and swordfish

Vol. 3: 1-5, 2010
Journal of Oceanography, Research and Data
Atlantic bluefin tuna (Thunnus thynnus) and swordfish
(Xiphias gladius) catch distributions observed during
driftnet fishery in the Northwestern Mediterranean Sea
(2000-2003 database)
BĂNARU Daniela.1,2*, DEKEYSER Ivan.1,2, IMBERT Guy. 1,2, LAUBIER Lucien. 1,2†
1)- Université de la Méditerranée, Aix-Marseille 2
2)- CNRS, Moyens communs du Centre d’Océanologie de Marseille, UMS 2196
Station Marine d’Endoume, rue de la batterie des Lions, 13007 Marseille, France
*)
Corresponding author: (D. Bănaru) Tel.: +33 491041628; Fax: +33 491041635
E-mail address: [email protected]
____________________________________________________________________________________
ABSTRACT: Atlantic bluefin tuna (Thunnus thynnus (Linnaeus, 1758)) and swordfish (Xiphias gladius
Linnaeus, 1758) are pelagic, migratory species, with high economic value. They are currently heavily
exploited. Many recent works have shown the importance of knowing the spatial distribution of these
species. This study presents an important and unique database of these species’ catch distributions
observed during driftnet fishing in the northwestern Mediterranean Sea in 2000-2003. Created by a
concerted effort between the fishermen and the scientific team from the “Centre d’Océanologie de
Marseille”, the database, composed of 2393 fishery reports concerning 51 fishing boats and validated by
74 scientific observers, was realised for an expertise funded by the Council of the “Région ProvenceAlpes-Côte d’Azur”. Only 20% of the fishery records, those from the “scientific” database, were
previously published and analysed. This article presents the entire database.
_____________________________________________________________________________________
KEY WORDS: Atlantic bluefin tuna, swordfish, driftnet, CPUE.
ACRONYMS
CPUE: Catch Per Unit Effort
ICCAT: International Commission for the Conservation of Atlantic Tuna
FAO: Food and Agriculture Organization
_____________________________________________________________________________________
Introduction
Atlantic bluefin tuna (Thunnus thynnus (Linnaeus, 1758)) (ABFT) and swordfish (Xiphias gladius
Linnaeus, 1758) have been continually exploited in the Mediterranean Sea for thousands of years (Mather
et al., 1995; Imbert et al., 2007). Atlantic bluefin tuna has been heavily exploited over its entire spatial
distribution (Atlantic and Mediterranean) for a decade and its associated fishery has become a highly
profitable commodity following the increase in demand from the Japanese market (Fromentin and
Powers, 2005; ICCAT, 2007).
Atlantic bluefin tuna and swordfish are both pelagic, migratory species with high economic value.
Large uncertainties in the basic fisheries statistics for the East Atlantic and Mediterranean Atlantic bluefin
1
Atlantic blue fin tuna and swordfish catches –Mediterranean Sea
tuna together with the lack of knowledge about key processes in its population dynamics (reproduction,
migration and population structure) have strongly influenced, and possibly biased, the perception of
Atlantic bluefin tuna stocks (Fromentin and Powers, 2005). These authors indicate that the spatial
dynamics of ABFT is central to understanding the population dynamics of this species, which is in
agreement with some recent studies which suggested juvenile and adult tuna aggregate along ocean fronts
(Royer et al., 2004; Zainuddin et al., 2008). These associations are likely to be related to foraging
(Atlantic bluefin tuna and swordfish feed on the abundant vertebrate and invertebrate prey concentrations
in these areas), but their respective distributions may also be environmentally driven (Ravier and
Fromentin, 2004; Imbert et al., 2007; Corbineau et al., 2008). For Royer et al. (2008) the patterns of
variation in fisheries’ time series result from a complex combination of both species and fisheries
dynamics coupled with environmental forcing (including climate and trophic interactions). The
Northwestern Mediterranean Sea represents an important part of the migration routes of Atlantic bluefin
tuna (Fromentin, 2009) and is probably a key feeding ground (Mather et al., 1995). Imbert et al. (2007)
tried to relate Atlantic bluefin tuna and swordfish distribution with the environmental parameters, fronts,
and forage areas using remote sensing satellite data.
The aim of this paper is to release to the scientific community an important and unique database of
Atlantic bluefin tuna and swordfish catch distributions observed for the driftnet fishery in the
Northwestern Mediterranean Sea during 2000-2003 and realised as a coordinated effort between the
fishermen and a scientific team from the “Centre d’Océanologie de Marseille”.
Methods:
Description of the fishery
Driftnet fishing, also called “Thonaille” (French term) is a pelagic, traditional fishing technique
conducted in the Northwestern Mediterranean Sea, along the French coast (Figure 1). This fishery targets
mainly 2-3 year old Atlantic bluefin tuna with a body mass ranging between 10 and 20 kg (89% of the
Atlantic bluefin tuna catches) and secondary swordfish. Past studies found that Atlantic bluefin tuna
mature at approximately 4 years old in the East Atlantic and Mediterranean Sea (length at maturity is
about 110-120 cm and weight 30-35 kg) (Mather et al., 1995). We may thus consider that this fishery
targets mainly juvenile Atlantic bluefin tuna. Both species represent about 82% in biomass and 94% in
number of the total annual catch by the driftnet fishery.
Nice
Sète
Toulon
Figure 1: Spatial distribution of the driftnet fishery reports from the Professional database (P, indicated
by empty dots) and the Scientific database (S, indicated by filled dots) in the Northwestern Mediterranean
Sea in 2000-2003.
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Bănaru et al. (2010) JORD 3:1-5
This technique is practiced in surface waters, during calm weather, in full darkness conditions, and
offshore where depths reach 2000-2500 m, along the border of the abyssal plain several tens of kilometres
off the coast. In the Gulf of Lions, driftnet fisheries are also located over shallower depths (50-100 m).
Boats operate on a daily rythm and carry no refrigerating equipment. Fishermen set and haul their net
once per night, and disembark their catch each day in the nearest fishing harbour. About 70 boats of 8.6 to
17.6 m long (mean length 12 m) are fishing in this area. Most of the boats weigh below 10-tons (gross
tonnage) and have less than 175-kW in motor power.
The nets used by fishermen are driftnets, composed of a single sheet of large mesh (90-120 mm),
woven with multihead nylon, set at the subsurface and let loose within the first meters of the surface
water layer. Imbert et al. (2007) indicated that a “Thonaille”-style gillnet is not a driftnet in the usual
sense and is characterized by inertial oscillations and little, if any, drift. However, driftnet is the term used
to designate such fishing gear by the FAO (UN Food and Agriculture Organization) or by Regional
Fisheries Management Organisations, such as ICCAT (International Commission for the Conservation of
Atlantic Tunas). The average height of a driftnet used by this fishery is 9 m (between 8 and 10 m) and the
length from 3000 to 11,300 m. The driftnet length depends on the crew size: it is generally constant for a
boat, but may vary according to sea conditions and to catch likelihood. A full description of this fishery is
in Imbert et al. (2001, 2002, 2007).
Database
The database presented in this paper was funded by the Council of the “Région Provence-AlpesCôte d’Azur” and created by the “Centre d’Océanologie de Marseille”. Dr. Guy Imbert was the
coordinator of this project and organised the scientific survey. Data were collected seasonally between
March and October in 2000, 2001, 2002 and 2003. The database is composed of 2393 fishery reports
(Table 1).
Table 1 Number of fishing reports registered in the driftnet fishery database.
Database
Source
Scientific
Professional
Total
2000
2001
2002
2003
2000-2003
%
on-board survey (Sb)
68
94
102
65
329
13.8
in-harbor survey (Sh)
70
9
52
37
168
7.0
Fishermen logbooks (P)
729
391
448
328
1896
79.2
867
494
602
430
2393
Scientific data (on-board or in-harbour surveys) were collected from 51 fishing boats. To preserve
confidentiality, a code number designates each boat. Fishermen agreed to collaborate and allow on-board
and in-harbour monitoring for the 74 observers from the “Centre d’Océanologie de Marseille” scientific
team.
The “professional” database was constructed with data registered in the fishermen’s personal
logbooks. Cross-examination of all these records permitted the professional reports to be validated and
also emphasized the high level of redundancy between data collected on-board, data collected in-harbours
and data registered in the fishermen’s logbooks. When we had two or three reports (on-board, in-harbour
and fishermen’s logbooks) for a single fishing operation we chose to include only the on-board report in
the database.
Imbert et al. (2001, 2002, 2007) published and analysed only 20% of these reports representing the
“scientific” database. Our paper presents the entire database, which now consists of 80% reports from
fishermen (professional data) and 20% from the scientific data (on-board, in-harbour surveys) (Table 2:
Data in supplementary file). Each fishing report includes information about date (day/month/year), boat,
driftnet length, position (initial coordinates), and catches (species, number and weight).
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Atlantic blue fin tuna and swordfish catches –Mediterranean Sea
Numbers and weights are pooled for the same fishing operation. There is no individual weight in
the database except for some large individuals, and this information is available in paper format only. An
Atlantic and Mediterranean size limit of 6.4 kg (age 2) has been in force since 1975; this is the reason
why ABFT catches were indicated separately in Table 2 for individuals larger and smaller than 6.4 kg.
This limit was recently raised to 10 kg for the Mediterranean Sea (Fromentin and Powers, 2005). A limit
of 10 kg was also established for the swordfish. CPUE (catch per unit of effort) was indicated for each
report and fish species and was calculated as a ratio between catch weight and net length.
Table 2 Atlantic bluefin tuna (Thunnus thynnus) and swordfish (Xiphias gladius) catch distribution
realised in 2000-2003 by the French driftnet fishery.
No = number of fishing report,
Db = database (P = professional database, Sb = scientific database, on-board survey, Sh = scientific
database, in-harbour survey),
Boat = code number of the boat,
NL = net length (km),
D = Day, M = month, Y = year,
Long = Longitude (ºN),
Lat = Latitude (ºE),
n = number of individuals caught,
W = total weight (kg),
L = lost fish,
CPUEt = Atlantic bluefin tuna catch by unit of effort,
CPUEx = swordfish catch by unit of effort,
- = no available data.
No
Db Boat NL D
M
Y
Long
Lat
Thunnus thynnus
>6,4kg
1
2
3
4
5
6
7
8
9
10
P
P
P
P
P
P
P
P
P
P
16
1
16
23
29
31
33
34
1
23
7,4
9,2
7,4
4,5
6,0
4,3
7,4
5,0
9,2
4,5
22
23
23
23
23
23
23
23
24
24
5
5
5
5
5
5
5
5
5
5
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
5,37
7,08
4,98
7,77
7,10
7,08
6,85
7,50
7,42
7,75
Xiphias gladius
<6,4kg L CPUEt >10kg <10kg CPUEx
n W n
42,63 8 55 12
43,03 7 82 9
42,70 0
0
2
43,10 11 163 1
43,03 2 50 10
43,03 1 54 0
42,95 5 97 15
43,23 6 79 0
43,13 16 210 9
43,08 10 187 20
W
48
27
9
3
28
0
41
0
26
51
n
-
W/NL
13,9
11,8
1,2
36,9
13,0
12,6
18,6
15,8
25,7
52,9
n
0
1
0
0
0
1
3
2
3
1
W
0
76
0
0
0
100
201
158
93
93
n W
0 0
1 5
0 0
0 0
2 14
0 0
0 0
0 0
1 6
0 0
W/NL
0,0
8,8
0,0
0,0
2,3
23,3
27,2
31,6
10,8
20,7
2 30
2 65
0 0
0 0
0 0
0 0
2 15
0 0
5,1
10,2
2,3
0,0
Complete data are available in the supplementary file
2390
2391
2392
2393
P
P
P
P
21
40
40
9
5,9 18 9
6,4 19 9
6,4 26 9
3,0 2 10
2003
2003
2003
2003
4,62
7,75
7,45
4,16
42,50
43,20
43,21
43,21
8
0
1
3
100
0
13
65
0
0
1
0
0
0
0
0
0
0
0
0
16,9
0,0
2,0
21,7
Acknowledgments
This project was funded by the Council of the “Région Provence-Alpes-Côte d’Azur” who also
permitted the publication of this database. Many thanks to the captains and fishermen of the 51 boats who
collaborated on this project: Adeline-Kévin, Alain II, Angelika, Anna-Félicienne, Annonciade, Charcot,
Charly-Christ, Cigogne, Corail, Daurade, Dragon II, Eloi Bernard, Geneviève, Gilsand, Hardi, Idéfix,
Jean-Christophe, Jean-Emmanuel, Jean-Marie-André, Jeanne d’Arc, Jessica, La Rafale, La Santa, Les
Copains, Loup Bar, Lulu IV, Marco, Neptune III, Notre Dame du Grau, Notre Dame du Rouet, Norville,
Océane, Orchidée, P’tit Bosco, Prince des Mers, Prosper, St Louis, Sainte Marie, San Antonio, Saphir,
Sergéric, Shark 3, Shark 4, Sonia IV, Le Sanaryen, Tchi Tchao, Thido, Tiki II, Valé, Valmar and Yves
Julien.
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Bănaru et al. (2010) JORD 3:1-5
Thanks also to the persons who realised the scientific survey of the catches and landings of the
fishing boats: Allanic Y., Astruc G., Atay A., Autran S., Bachet F., Bichel M., Bonnaud E., Bouchard O.,
Bouillac G., Bourreau S., Bourret V., Brossard C., Brutinel C., Calcat C., Carteron S., Cerbone S., Cérutti
F., Chazon M., Contino F., Couthon C., Dalègre K., Delaunay A., Delord K., Desmond G., Diéval E.,
Dollé N., Douroux C., Duhem C., Fauconnier G., Favreau-Bikoff V., Ferré B., Fornier M., Ghazania F.,
Gimenez P., Girard C., Glatz N., Grondin J., Guerri F., Hugon V., Jackovsky J., Laudet I., Lefèvre C.,
Maixandeau A., Marteau-Delphin A., Mas V., Masseboeuf O., Massie A-L., Matho M., Mérigot B.,
Morrin E., Mourand L., Mouriès M., Nassar K., Négrel S., Niesten P., NGuyen D., Nourrisson C., Olivès
M., Perriez A., Politi F., Roche V., Sanguinède F., Sanchez S., Soussiguian C., Tailamé Y., Thuillier D.,
Tolla C., Touitou M., Uitz J., Vettoretti A., Villeneuve M. and K. Volpatti.
We are grateful to Paul Nival, Mireille Harmelin-Vivien, Philip Trevelyan, Jennifer Guarini and
the two anonymous reviewers for helping us to improve the manuscript.
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