SCRS/2009/189
THE EASTERN ATLANTIC BLUEFIN TUNA: ENTANGLED IN A BIG MESS, POSSIBLY
FAR FROM A CONSERVATION RED ALERT.
SOME COMMENTS AFTER THE PROPOSAL TO INCLUDE THE BLUEFIN TUNA IN
CITES APPENDIX I.
Di Natale A.1
SUMMARY
The Eastern Atlantic Bluefin Tuna (Thunnus thynnus) is facing a difficult management situation since
more than one decade, when the tuna caging activities had begun to be common in several
Mediterranean countries, inducing a sort of “gold rush” and a lot of additional problems in the data
collection. This was the major issue, along with the prolonged data deterioration and the following
growing unreliability of the stock assessments carried out by SCRS/ICCAT.
But these are only the last issues of an old situation where partial and unreliable data, a very partial
biological knowledge of this species, a marginal ethological knowledge, and a very minor knowledge
of the effects of environmental changes on bluefin tuna biology and distribution, along with some
scientists reading only a part of the immense literature on bluefin tuna are feeding a sort of incredible
game, where some economic interests are trying to push the free fishery (or, on the opposite, a closed
fishery when necessary) and environmental groups are pushing for a full protection of the species, to
prevent an hypothetical collapse.
It is hard for a scientist following this fishery and the ICCAT meetings since decades to assist in
silence, looking at this dispute going on in various fora. It is difficult particularly because most of the
individuals concerned are good scientists and because the conservation of this species is a must, along
with the ancient culture linked to this fishery. It is difficult exactly like finding reliable data to bring
the discussion along the reality.
In this paper, the author discusses the main issues, on the basis of his experience at sea and in various
international scientific fora, trying to provide more arguments for discussion and a better
understanding of the situation, with the purpose to help in bringing the analysis on the status of this
iconic species as much as possible along a rail of reality.
KEYWORDS
Bluefin tuna; Conservation; CITES; ICCAT; Population structure; Catch composition; Data collection; Pelagic
fisheries; Large pelagic species; Overfishing.
1
Aquastudio Research Institute, Via Trapani 6, 98121 Messina, Italy
1.
Foreword
This paper is not a traditional scientific paper. It is mostly a sort of independent short revision of an
huge and even largely incomplete amount of scientific papers, ICCAT reports and various types of
documents about the situation of the most important species managed by ICCAT, the bluefin tuna
(Thunnus thynnus, Linnaeus) which rapidly became an icon for many environmental organisations
and the media and a big business for some commercial entities.
This paper is mainly a desperate tentative to bring the discussion on the bluefin tuna along a rail of
reality, taking into account all the many troubles about the controversial status of this species, the
data issues and the general knowledge, as well as the impact of various assessments and papers on
the actual situation.
2.
Introduction
According to archaeological findings, the bluefin tuna (Thunnus thynnus, Linnaeus, 1758) was
firstly exploited in the Mediterranean Sea more than 11200 years ago. The first document known on
the bluefin tuna fishery is engraved on the walls of the Genovese’s Cave in the isle of Levanzo
(Egadi Islands, W. Sicily, Italy), dated about 9,200 years b.C. It is clear that, since these remote
times, bluefin tuna was regularly a common food resource for the Mediterranean inhabitants and a
basic component in their diet (Curtis, 1991; Powell, 1996). Later images, like the “Siciliota” pottery
from the IV century b.C. kept at the Mandralisca Museum in Cefalù (Sicily, Italy), show a common
trade of bluefin tuna, that was marketed fresh at that time.
Figure 1 – The engravings of tuna and dolphins along the walls of the Genovese’s Cave in the Isle of
Levanzo (Egadi Isle, Western Sicily, Italy), 9,200 b.C.
Figure 2 and 3 – Tuna market depicted on a Sicilota pottery (IV b.C.)
Evidences of tuna factories were found in many places along the coasts of the Mediterranean Sea
and even inland, like in the Roman ruins in Madrid. The history of the long exploitation of the
bluefin tuna is strictly linked to the Mediterranean culture and several tracks can be easily found in
many classical works from the II century b.C. to the II century a.D. (see the reprinted works by
Plinius, 1553; Esopo, 1592; Aritotelis in Athaeneus, 1653; Athaeneus, 1653; Parthenii, 1689;
Oppianus, 1738), but including also Strabonium, Eschilus, Homerus, Solinus and Eustazius.
Relatively more recent transcriptions about ancient and historical information can be found also in
Mattioli (1568), Gesner (1606), Aldrovandi (1638) and Jonstonius (1649).
A careful reading of these classical works reveals not only the long fishing activities, but also many
interesting aspects of the bluefin tuna biology and ethology, which are often forgotten and
sometimes rediscovered ex-novo by several young colleagues. The most interesting information is
related to the periodical migrations between the Black Sea and the Eastern Mediterranean Sea
(Plinius, 1553; Aristotelis in Athaeneus, 1653), confirming the existence of a possible
subpopulation in the Black Sea till recent times and the environmental collapse happened in this
Sea, discussed in a following part of this document.
The biology of the bluefin tuna (Thunnus thynnus, Linnaeus, 1758) an particularly of the Atlantic
populations is that of a marine top predator having a long natural history. Many aspects of his
biology and stock composition are well known (Arena et al., 1980; Aricò & Genovese, 1953; Bard
et al., 1978; Block et al., 1978; Collette et al., 2001; Cort, 1990; De Metrio et al., 2003a, 2003b;
Dicenta & Piccinetti, 1977; Di Natale, 1988b, 1989, 2004b, 2007; Di Natale et al., 2002, 2005b,
2006b, 2006c; Farrugio, 1980; Frade, 1925; Ely et al., 2002; Fromentin et al., 2000; Genovese,
1953a, 1956, 1958; Gordoa et al., 2009; Heldt, 1927, 1932; Karakulak et al., 2004; Liorzou et al.,
2001; Mather et al., 1974, 1995; Morovic, 1961; Oray et al., 2005; Oray & Karakulak, 2005;
Piccinetti, 1973; Piccinetti-Manfrin, 1970; Piccinetti et al., 1977, 1995; Richards, 1976; RodriguezRoda, 1964; 1967; Roule, 1913, 1914a, 1914b, 1916a, 1916b, 1917a, 1917b, 1917c, 1918, 1919,
1921, 1923, 1925; Safina, 2001; Sanzo, 1909, 1910; Sarà, 1973; Scordia, 1930, 1931, 1933, 1934a,
1934c, 1935b, 1936a, 1937a, 1937b, 1938b, 1939a; Sella, 1924; Spagnolio, 1938), while many
others are still unknown. The recent genetic studies sometimes provides useful pieces of the
biological puzzle of this species, wile some others are putting new questions )Alvarado Bremer et
al., 2005; Broughton & Gold, 1997; Carlsson et al., 2004; Clark et al., 2004; Ely et al., 2002;
McDopwell et al., 2002; Tagaki et al., 1999)
The fishery of the bluefin tuna is also a part of the story of the human bean: besides of the tuna
traps, that we discuss later on in details, the fishery was always a mirror of the advanced
technologies, starting from simple hand lines to the modern and sophisticated tuna purse-seiners
(Arena, 1982d; Arena et al., 1980; Arena & Di Natale, 1987; Cau et al., 1999; D’Amanich, 1954;
De La Blanchère, 1868; Dieuzeide, 1931; Di Natale, 1988a, 1988c, 1990, 1991, 1999; Di Natale et
al., 1987, 1988a, 1988b, 1989, 1993, 1996, 2004; 2005a, 2005b, 2006a; Di Natale & Mangano,
2008; Doumenge, 1998; Duhamel de Monceaus, 1769-1782; Farrugio, 1978, 1980; Ferraro, 1986;
Fromentin, 2002, 2003; Gordoa et al., 2004; Heldt, 1932; La Marhadour, 1914; Liorzou et al.,
2001; Mackenzie & Mayers, 2007; Mackenzie et al., 2009; Ninni, 1917, 1921a; Oren & Ben Tuvia,
1954, 1959; Parona, 1919; Pavesi, 1889; Piccinetti, 1980; Roule, 1914a, 1914b, 1916a, 1921; 1924;
1925; Sañez Reguart, 1781; Sarà, 1963; Scaccini, 1965; Scaccini & Biancalana, 1959; Scordia,
1934b, 1936b, 1940a). The recent adoption of the caging system in the Mediterranean to increase
the added value of the fattened tuna on the market can be tracked in the papers by Piccinetti (1980)
and Miyake et al. (2002).
The story of the bluefin tuna fishery shows also big temporal holes over the centuries, maybe
because it was a common activity and possibly the literature was mostly dealing with more elegant
issues. It is also true that the same holes exist in several natural history areas.
According to what Aristotelis (in Athaeneus, 1653) said, “thynnum esse tradit gregalem ac locum
mutare”, this species is a very migrant one, able to cross the ocean in a short time, and to carefully
read the chemical and physical messages from the sea waters. The bluefin tuna migrations are huge
and only partly known even today. Big changes in the distribution pattern have been reported so far,
but most of them are known in the last century (Aloncle, 1964; Arena, 1971; Cort & Rey, 1983;
Genovese, 1959; Mather 1962a, 1962b; Mather et al., 1967, 1974, 1995; Naccari, 1872; Ninni,
1922; Rey, 1979, 1992; Rivas, 1976; Rodriguez-Roda, 1980; Rooker et al., 2007; Roule, 1924b;
Sarà, 1963, Scordia, 1938, 1939a, 1940b; Sella, 1929).
It is very difficult to track the story of this fishery along the centuries till the XVI century, because
the information is scattered in poems, literature, romances and commercial notes. Only from 1500
on it is possible to find some good reports and even figures and engravings, beginning from Braun
& Ogenberg (1572-1617), which help us to better understand how the exploitation was developed in
the last 500 years.
But it is not the case to re-write this long story, because it is written and well described in many
papers, here included in the bibliography, which is anyway largely incomplete2. Anyway, it is
important to recall in our mind some important steps of the bluefin tuna fishery over the centuries
and particularly in the most recent times, trying to better understand the actual situation.
At the same time, it is important to point out the incoherencies and the holes in our current
knowledge, with the purpose to address in the proper way the various issues.
3.
The trap fishery
The tuna trap fishery was apparently initiated by Phoenician, and then continued by Romans and
Arabs, and all the following people inhabiting the costs of the Mediterranean, the adjacent areas in
the Strait of Bosphorus and the South Spanish and South Portuguese coast in the Atlantic Ocean.
It is not clear to understand with which gear this fishery was carried out in ancient times. According
to some early engravings at the end of the XVI century (Braun & Hogenberg, 1572-1617), it is sure
that tuna traps were using not only set trap nets, but also huge beach seines, sometimes of various
types. This is something not commonly known, having a great relevance to better understand the
distribution of tuna schools, that were clearly very close to the coast at that time.
Later on and particularly in the XVIII century, there are not many tracks of these beach seines,
while the set tuna traps have a lot of detailed information and many drawings and engravings can
tell us a lot of details (Cetti, 1777; Duhamel de Monceau, 1769-1782; Gaetani, 1797; Gaetani di
Villabianca, 1795; Mongitore, 1743; Pugnatore, 1595; Sarmiento, 1757). On the contrary, the
information about the distribution of tuna traps along the coasts is very incomplete and only in a
few areas there is a good list of the tuna traps active at that time.
Several tuna traps were used also to catch small tuna species other than the bluefin tuna (Cattaneo
Vietti & Bava, 2009), and this fact caused some confusion in the past to properly understand the
number of traps effectively targeting the bluefin tuna.
At the end of the XIX century there are good maps available and then there is the possibility to
better understand how and where the bluefin tuna issues was carried out at that time, mostly by
using the maps provided by Pavesi (1899) and Parona (1919).
2
The authors apologises for all the omissions in the bibliography, due to time constrains that prevented mostly a deep
analysis of the many scientific papers presented to SCRS-ICCAT in the last decades, which have been anyway
considered in the text. The literature included in this text is mostly dedicated to papers which are often forgotten or
other relevant scientific works. Each omission is not by deliberate will.
Many other scientific works report data on tuna trap fishery (Alliata, 1951; Angotsi, 1901;
Anonimous, 1952; Arena, 1963, 1985, 1986; Arena & Li Greci, 1970; Avolio, 1805; Belloc, 1961;
Consolo, 1987; Costanza, 2000; D’Amico, 1816; Dean et al., 2003; De Cristofaro, 1970; De
Miranda y Riveras, 1927; De Salas & García Solá, 1876; Di Natale, 1988a, 1990, 1991, 1999, 2008;
Di Natale et al., 2006a; Di Natale & Notarbartolo di Sciara, 1994; Doumenge, 1998; Roule, 1926;
Genovese, 1952, 1953b, 1960; Guaiana, 2000; Guggino, 1977; Guggino et al., 1977; Lemos &
Gomes, 2004; Li Greci et al., 1991; Lippi Guidi, 1993; Lo Curzio & Sisci, 1991; Maggio, 2001;
Manetti, 2001; Mariotti, 2003; Mert et al., 2000; Militello, 1937; Mondardini, 1999; Ninni, 1921b,
Ravazza, 1999, 2000, 2002, 2003, 2004, 2005; Ravier-Mailly, 2003; Roule, 1921; Rubino, 1995;
Sarà, 1983, 1988; Scaccini, 1965; Scordia, 1925, 1930, 1931, 1933, 1934a, 1936c, 1937c, 1939b;
Sechi, 1918; Volpi Lisjiak, 1996).
Table 1 shows in a very clear way that the number of tuna traps were very important in the
Mediterranean and in the adjacent areas and, at the same time, that the number of traps in each
country varied very much in the short period taken into account by Pavesi (1899) and Parona
(1919).
Table 1 – Overview of the available knowledge on the tuna traps noticed in the Mediterranean Sea and
adjacent areas in 1899 and 1919.
Pavesi, 1899
Country
Turkey
Parona, 1919
1919/1899
active inactive total active inactive total
26
0
26
0
26
0
0
1
31
0
31
+3100%
41
99
140
51
81
131
-6.4%
France
5
21
26
10
21
31
+19.2%
Spain (Mediterranea coast)
6
24
30
9
13
22
-26.7%
Morocco4
0
0
0
0
0
0
0
Algeria
0
2
2
1
0
1
-50%
Tunisia
1
2
3
1
1
2
-33.3%
Libya
0
0
0
2
0
2
200
Malta
2
1
3
2
1
3
0
Total Mediterranean
81
150
231
133
116
249
7.8%
Spain (Atlantic coast)
9
2
11
8
13
21
90.9%
14
10
24
15
6
21
-12.5%
104
162
266
156
135
291
9.4%
E. Adriatic3
Italy
Portugal
Total tuna traps
26
variation
How these variations can be interpreted is not easy: in some cases there was an export of know-how
from some countries to others, in some other cases they were possibly caused by a different
availability of the bluefin tuna in some coastal areas, either in a positive or negative sense. Due to
3
It was decide to use “East Adriatic” to include all the tuna traps noticed in various Countries of that coast, because the
mane and boundaries were modified many times over the last century.
4
It seems that Morocco had some active tuna traps at that time, but this information was not included in the reviews
from Pavesi and Parona and it is possible included in some Portuguese archives.
the fact that tuna farms were industries, the economic factors could be also a part of these changes
over the time, but a much more deep and specific analysis is necessary to explore the data, while the
detailed information is not available for most of the factories and it is often preserved in handwritten old logbooks. In other cases, economic information can be found in official publications
dealing with annual permits or annual catch reports.
At the same time, it is important to note the stability reported in Malta, possibly as the result of no
relevant changes in this key area in the central Mediterranean Sea, and in Turkey, where the number
of the many tuna traps was stable over these 20 years. This last situation is particularly relevant,
because it is strictly related to the migration of bluefin tuna from the Black Sea to the Aegean Sea
and viceversa, a situation which had completely changed in the last part of the XX century
(Devedian, 1926; Iyigungor, 1957; Karakilak, 2000; Mert et al., 2000; Sarà, 1963). At the same
time, the relevant number of Turkish traps at the beginning of the XX century confirms the massive
presence of bluefin tuna in this extreme Eastern Mediterranean area, supporting the economy of 26
factories.
Tuna traps were often very concentrated in some coastal areas, where the passage of bluefin tuna
was more abundant or common and the map provided by Parona (1919) is able to give a clear
overview of the distribution of tuna traps along the coasts (see Figure 4a and 4b).
From the maps provided both by Pavesi (1889) and Parona (1919), it is very clear that the areas
having the highest concentration of tuna traps were those in the central Mediterranean Sea, with
other peaks at the two geographical extremes, close to the Strait of Gibraltar and the Strait of
Bosphorus.
The tuna trap fishery, according to Avolio (1805), was carried out in the Mediterranean from March
to June in the XVIII century. This period is slightly different from the actual one, which is usually
from May to June. The fishing season is broader if the tuna traps located in the Atlantic are taken
into account, because in this area the fishery is carried out from April to August.
Figure 4a (left) and 4b (right) – Detailed map concerning the location of the tuna traps in the various
countries of the Mediterranean Sea and adjacent areas (Parona, 1919).
Actually, there are only a few traps still active and not all of them are fishing every year. Seventeen
traps are active in Morocco (all in the Atlantic, but with 7 new traps activated since 2007), five are
in Italy (only three, all located in Sardinia, were fishing in 2009), four are in Spain (all in the
Atlantic) and one is in Libya, while others in various places still have their nets and equipment but
are not active anymore.
The tuna trap fishery has a very high cultural and socio-economic value and some countries had
already officially recognised it. The buildings forming the land structure of each tuna trap have a
very high historical and architectural value, sometimes recognised also by the UNESCO. The huge
staffs working in each tuna trap and the Rais (the specialist in charge of heading and driving the
fishing activities) have all a very high specialisation, and they cannot be easily replaced and their
knowledge is a patrimony to be preserved, as well as for the other aspects of the tuna trap fishery.
The most important point that is necessary to discuss in this paper is why this fishing activity had so
many changes over the time and in which way they can help in better understanding the current
problems of the bluefin tuna. It is sufficiently clear that several changes in the tuna trap fishery are
strictly related to problems which are far from the total abundance of the biomass in the area
(Mediterranean and Atlantic together) and this can provide arguments for our discussion.
The complexity of the various situations needs to restrict the analysis to a few points, which appear
particularly interesting: the lower availability of bluefin tuna along most of the coasts and the total
disappearance of the Turkish traps in the Bosphorus in the last quarter of the XX century.
The first point is maybe the most difficult to examine, because it concerns mostly the alteration of
the coastal environment over the time. The increasing number of new and big harbours in all
countries, the incredible increment of the inhabitants along the coast, the concentration of several
production and industrial activities in coastal areas and the modification of the quality and quantity
of river inputs to the sea had progressively caused many alteration of the chemical and physical
parameters of sea-water in coastal areas.
Furthermore, the level of noise had incredibly increased, at first at the end of the XIX century, when
engines were largely introduced in merchant marine and in the military vessels, and after the 2nd
World War when engines were commonly adopted also by fishing vessels and leisure boats. It is
difficult to specifically attribute values to each single locations, but there are several scientific
evidences about the impact of anthropogenic activities on some tuna traps (Addis et al., 2008; Di
Gregori & Massoli-Novelli, 1992; Grassi, 1913; Mazzarelli, 1917).
This resulted in a decreasing availability of the bluefin tuna in various areas independent from the
total abundance of the stock. It is clear that bluefin tuna moved from coastal waters to more
offshore waters (more clean and quite) in several areas, but they continued to pass along the historic
migration courses in some areas. These facts will provide a different key to read the yields history
in this fishing activity and possibly even in others.
The second point is one of the less considered one when discussing about the Mediterranean
populations of bluefin tuna within the larger East Atlantic stock: the issue of the Black Sea bluefin
tuna sub-population. Since historical times there are many evidences of massive movements of
bluefin tuna from the Black Sea to the East Mediterranean for spawning (figure 5) and then again
back to the Black Sea for wintering.
Figure 5 – The typical migration of bluefin tuna in the Black Sea, the Bosphorus and the Eastern
Mediterranean (Sarà, 1963).
This sub-population was there for many centuries till the second part of the XX century, when it
suddenly almost disappear. Zaitsev and Mamaiev (1997) and Kideys (2004) shown how fast the
decrease of the population happened, till the disappearance of any catch of bluefin tuna in the Black
Sea waters of Bulgaria around 1971 (figure 6). The bluefin tuna finally disappeared completely
from the Black Sea, even from the Turkish waters close to the Bosphorus, in 1988.
Figure 6 – The fluctuation of fish abundance in the Black Sea according to the data from the Bulgarian
fishery. Catch curve concerning Bluefin tuna is marked as 1 (Zaitsev & Mamaiev, 1997).
Even in this case, besides the opinion by Daskalov (2003), the abundance in the Black Sea area
seems that was not related to a direct fishery, but it was affected by several collapses in the Black
Sea environment (partly related to fishery issues), which apparently forced the remaining bluefin
tuna population to move into the Mediterranean Sea. There are no scientific studies about the
further distribution of this sub-population in the Mediterranean, but it is strongly suspected that
these tunas remained mostly in the Eastern part of the basin, because of their natural history
tradition and the quality of the water there. This fact can be a part of the reason why the Turkish
fishery obtained so good results in the last part of the XX century and why genetic studies reveals a
difference between east and west tuna subpopulations in the Mediterranean Sea (Carp, 1951;
Devedjian, 1926, Iyigungor, 1957; Karakulak, 1999, 2000, 2003; Karakulak & Oray, 2009; Kideys,
2004; Merty et al., 2000; Oray et al., 2005; Piccinetti et al., 1995; Piccinetti-Manfrin et al., 1995;
Sarà, 1963; Tekin, 2000; Zaitsev, 2003; Zaitsev & Manaiev, 1997). This was also the possible
motivation for closing the Turkish tuna trap activities in the Strait of Bosphorus. Even in this case,
again, it is clear that the bluefin tuna abundance in the various areas was mostly affected by
environmental and behavioural factors other than direct fishery ones.5
4.
The behavioural aspects
The bluefin tuna is a well evolutes species and a marine top predator. The behaviour is a very
important and essential component of its life, even if we know only a few aspects of the bluefin
tuna behaviour.
Ancient papers provided much information about the apparent behaviour of this species, while
several papers in the XVII, XVIII and XIX centuries improved our knowledge, because scientists
were spending a lot of time at sea, or in fishing areas, or collecting direct information from the
fishermen. Only in the last part of the XX century, by using more modern technologies, it was
possible to betters study some behavioural and ethological aspects of bluefin tuna, particularly in
the Mediterranean Sea.
Thanks to the experience obtained by the use of aerial spotting to better catch the bluefin tuna with
the modern Mediterranean purse-seiners6, the distribution and composition of the various schools of
bluefin tuna were studied by aerial observations by Farrugio (1979), Arena (1980, 1981, 1982a,
1982b, 1982c) and Fromentin et al. (2003). It was clear that the composition of each tuna school
was correlated to a very precise strategy of the bluefin tuna, particularly during the spawning
period. In these years, the shape and composition of the various groups of bluefin tuna were deeply
analysed and revealed complexities not known before.
From figure 7 (Arena, 1982a) it is clear that the strategy adopted by each school in the genetic
period was able to affect the size frequencies in catches, but this fact is never taken into account
when catch are analysed or used in VPA. Not all schools are the same in size composition, even in
the same area. The aerial observations were checked with landing controls, having a direct and
scientific confirm of the size frequencies reported by the observers. The fishermen’s choice is an
important component of this fishery, together with the school composition and those factors
combined are able to strongly interfere with our understanding of the size composition of the stock.
This is particularly relevant also because purse-seine catches represent more than 80% of the East
bluefin tuna catch.
The effects of climate changes or oceanographic anomalies on Atlantic bluefin tuna behaviour,
particularly on the mass movements, are known since years (Fromentin 2002; Fromentin et al.,
2000; Di Natale, 2007; Lemos & Gomes, 2004; Mackenzie & Myers, 2007; Ravier-Mailly, 2003;
5
In recent times, with the partial improvement of the environmental situation in the Black Sea, bluefin tuna is slowly
reappearing in that basin. In 2007, late in November, a few specimens were caught in the Marmara Sea and in the
nearest areas of the Black Sea. In the same period, juveniles having a size (about 700 g) much lower that the usual size
at that time of the year were found on the market in Istanbul, providing the evidence of a possible reproduction in areas
having a temperature colder than in other Mediterranean areas.
6
The aerial spotting for fishing bluefin tuna is banned in the Mediterranean since 2006.
Ravier & Fromentin, 2004; Roule, 1921), but the recent mass movements of this species have not
been studied so far, particularly in the Mediterranean Sea.
Figure 7 – The most typical composition of bluefin tuna schools during the spawning season in the ‘80s. A:
cone-shaped formation; B: scale formation; C: caravan formation, having most of the individual spawning at
the surface. p: pilot specimens. (Arena, 1982).
The tuna school showed a different composition after the great change noticed around 1996, when
the major concentration of bluefin tuna moved away from the South Tyrrhenian Sea going to the
South Mediterranean and also to the East Mediterranean. This situation, possibly linked to
oceanographic factors (Di Natale, 2007), was partly reverted since 2006, when several groups of
spawners returned again in the South Tyrrhenian Sea. In the meanwhile, according to the catch
composition of purse seiners moved into cages, the schools were more mixed, with a higher
presence of new spawners (fish around year classes 3 to 4).
In the new situation, the typical shapes of the tuna schools in the spawning period as studied by
Arena (1982) became less defined, even if the “caravan” and “cone” shapes were among the most
frequent. But, even in these cases, the size distribution within the schools was more mixed and less
defined. Shortening the fishing period induced fishermen to maximize the yields and not to make
any choice among the schools depending on size composition.
A recent paper (Fromentin et al., 2003) confirms the relevance of the aerial surveys, either for
understanding the behaviour or to try to assess the presence and abundance of bluefin tuna in
various Mediterranean areas, even if there is a very scarce attention to the previous literature on this
subject. These fishery independent estimates could possibly correct some troubles in the current
assessments and all the available evidences show that the presence of bluefin tuna at sea is
considerably higher than the model estimated.
There are more issues concerning the behaviour, the ethology and the migrations of tuna which are
very relevant for a more general overview of the bluefin tuna situation.
One of the most important issue is the migration from and to the Mediterranean Sea. According to
the best available knowledge, the Mediterranean is the largest and most important spawning area for
the bluefin tuna, with a lot of internal movements, and the Eastern Atlantic stock seems to have a
peculiar size fidelity (figure 8). This factor was one of the most considered for taking the decision to
separate the two Atlantic stocks, which anyway have a low percentage of mixing rate. Every
scientist and manager following the bluefin tuna problems is well aware that the current
geographical division between the two stocks is artificial since the beginning and many efforts are
spent every year trying to find better justifications for this division or to propose more appropriate
modifications. SCRS was asked in the recent past to evaluate the management effect of moving the
separation in various ways and several mathematical efforts were spent to support the various
hypothesis, without finding a better management solution.
Figure 8 – Main migratory courses of the bluefin tuna inside the western and central Mediterranean
Sea during the spawning season, including pre- and post spawning movements known till the ‘80s.
(Sarà, 1983).
Furthermore, the problems are much more complex that they appear, because bluefin tuna has the
bad habit to non respect the various hypothesis suggested by scientists. As a matter of fact, bluefin
tuna had several non-regular experiences in the past and it is possibly having some more that we
don’t know.
The idea to visit for several years the North Sea up to the Norway (Gruvel, 1922; Heldt,1923, 1925,
1926; Le Gall, 1926) was not so good. It seems that bluefin tuna was attracted in these cold and
shallow waters mostly by the high availability of good food with a high fat content (herrings and
other species). Massive movements are historically reported and the very rapid disappearance of
this fishery (Figure 9, from 1950 to 1979) was the reason for a dedicated Symposium by ICCAT in
2008. There, it seems that a combination of environmental factors, decreasing of the prey species
due to overfishing and the high fishing pressure applied to the bluefin tuna in the short period were
all together responsible for this disappearance. Even in this case, several people reacted, claiming
for a disaster for the bluefin tuna and some others tried to reiterate the same in recent times.
1950-1959
1960-1969
1970-1979
1980-1989
1990-1999
2000-2007
Figure 9 – Geographic distribution of bluefin tuna catches per 5°x5° and per main gears (ICCAT, 2008).
A similar situation, but with even more unclear displacement happened between 1951 to1964
(Figure 9) in the SW Atlantic. This period was called “the Brazilian fishery” and it provided good
yields for several years. Then the massive presence of bluefin tuna decreased in a very short time
and apparently most of the specimens moved away from that area. There are not many good
scientific analysis or data about the reason for these movements.
There is another issue, which is possibly linked to the same area but it is very often forgotten by
most of the scientists working on bluefin tuna research. It was pointed out in the past for several
times mostly by Jones (1971), Rodiguez Roda (1980), Cort (1980), Arena & Cefali (1982) and
Arena (1982c, 1988). Some specimens were found during the fishing activity on Norway (Rodiguez
Roda (1980), while others were noticed in the Canary Islands (Cort, 1980); Rivas (in Arena, 1980)
reported that many specimens with these marks are commonly found among the bluefin tuna
catches in the Bahamas. Bluefin tunas with these marks were reported also by Heldt (1932) in Spain
and Morocco, but the marks were wrongly attributed to the Risso’s dolphin (Grampus griseus). In
the Mediterranean, since the ‘70s, several specimens of medium and large size bluefin tunas were
found with crater wounds in the lower posterior section of the body, in the perianal part (Figure 10).
Figure 10 – Descriptive figure of a large bluefin tuna having marks of Isistius brasiliensis (Arena, 1988).
These type of marks are typically caused by the bites of a small shark, Isistius brasiliensis (Quoy
and Gaimard, 1824), the smalltoth cockiecutter shark. This shark species is distributed in several
areas in various oceans, but its presence is common in the South Atlantic; it is usually a deep-water
shark (living down to 3500 m), but having nocturnal movements up to the surface. The bites of
Isistius brasiliensis leave natural marks able to be distinguished and identified for the entire life of
the fish. The percentage of bluefin tuna with these marks in the catches from the South Tyrrhenian
Sea varied from a minimum of 0.68% to a maximum of 2% in the 70’ and the ‘80s (Arena, 1982c,
1988; Arena & Cefali, 1982); almost the totality of these specimens were large males. Actually,
according to the observers reports, the presence of tuna with these natural marks is still reported
every year in the central Mediterranean.
These interesting and curious natural marks pose various problems in our understanding of the
bluefin tuna movements and those questions remain unsolved even after the various tagging
activities with pop-up satellite tags and archival tags carried out in the ‘90s and in recent years. As a
matter of fact, only one tagged bluefin tuna went from the Mediterranean to south of Capo Verde
Islands. It is very difficult to understand in which part of the Atlantic Ocean these marks are caused,
but it seems logical that these natural marks reveal movements which are not known by the
scientists and a possible different distribution (maybe vertical?) of medium and large males in some
parts on the Atlantic Ocean, before migrating to the Mediterranean for spawning.
There is another important issue, which is often forgotten when dealing with the Eastern Atlantic
stock of bluefin tuna. It is well known since the time of Plinius (I century a.C.), that an undefined
portion of the Atlantic bluefin tuna adult population remain in the Mediterranean Sea for an
undefined number of years (more than one year), wintering there. This point was raised many times
in the XX century (Genovese 1965; Scordia, 1934b, 1934c, 1935a) or even more recently (Di
Natale et al., 2005c, 2005d; ) and this part of the stock is certainly present in the deep central
Mediterranean waters (including the area of the Strait of Messina) and it should be possibly present
also in the Eastern Mediterranean, where it is supposed that a portion of the sub-population
originally located in the Black Sea might stay. The effects of these “resident” bluefin tunas on the
VPA have never been analised.
As it was explicitly mentioned in the external assessment of the ICCAT in 2008 (Hurry et al.,
2008), maybe there are too many ICCAT scientists knowing very well the mathematical models
while only a few scientists seem to really known the species and their life in the wild, often with an
unbalanced situation. This fact is creating a sort of parallel vision of what is happening in the
reality, relying much more on numerical data independently from their real meaning against the
evidence coming from the situation at sea, where not everything can be immediately translated into
numbers.
5.
The stock assessment
SCRS carried out several stock assessment of bluefin tuna and all of them were based on the huge
data bank kept by the ICCAT Secretariat, which includes the data transmitted by the statistical
correspondents sitting in each Contracting Party or fishing entity. Data provided by scientists during
the SCRS meetings are also included. The stock assessment methodology is mostly based on the
VPA with a lot of exploratory hypothesis or comparison with other methodologies when necessary.
SCRS and the ICCAT Secretariat have high level experts able to run these sophisticated models,
which are considered the best available on the scientific market. This situation, which appears as
one of the best among the various RFMOs, is not able to overcome a series of problems which are
knows since many years.
It is well known that VPA is a model widely used in many fisheries and for a broad range of
species, but it is not adequate to describe the enormous complexity of species having a huge
geographic distribution and very complex movements (even massive), either vertical and orizontal.
It relays mostly on total catch by gear, size frequencies distribution by gear, area and time strata,
recruitment and standardised CPUE series by gear (other inputs exists and others are also possible).
It provides a range of predictive hypothesis, which could be huge according to various choices,
taking into account the uncertainties inputted by the scientists. This is the best available tool at the
moment and this is the reason why it is adopted by SCRS and ICCAT, but everybody knows that it
is not a magic tool and its limits in describing large pelagic fish populations are well known by the
specialists. Anyway, this is what we have and we have to deal with it.
There is a very well-known sentence about the mathematic models: garbage in, garbage out. It is
often recalled during the SCRS discussion to underline the bad quality of several data sets,
particularly those on bluefin tuna and even more after the adoption of the quota system in 1996. In
the past, catch data were sometimes incomplete or missing for some Contracting Parties (the
statistical services were very different in each CP), but they were “honest” in their quality. Size
frequencies, biological data and CPUE were usually provided by scientists and, even if they were
often very localised, their quality was always considered sufficiently reliable.
When ICCAT decided to adopt and enforce the quota system for the bluefin tuna (was the first TAC
never adopted in the Mediterranean Sea and it is still the only one), than the “gold rush” started and
this was the cause of the incredible deterioration of the data submitted to ICCAT.
The data that were submitted by scientists at the end of the ‘90s were used by some CP to raise
issues about compliance with the ICCAT rules, even if this is not possible in theory. This fact
created an enormous trouble in the system, because scientists coming to SCRS meetings, and
particularly those working under contracts with national governments (the large majority), started to
pay a lot of attention to their data, avoiding to present data that were in contrast with the official
ones provided by the governments. It doesn’t mean that scientist manipulated their data: it simply
means that some data sets were not presented anymore. This fact is very evident when examining
the size frequencies and their distribution. Small tunas became rare in the reports, because the
undersize catches were not reported by many of the CPs.
This is a very relevant point, because it raises a couple of important and basic problems: the use of
scientific data for compliance issues and the direct detrimental effects on the assessment model.
The first one is a procedural problem, because scientific data must be always used only for
scientific purposes, to better understand the situation concerning a species and for suggesting the
necessary strategies to better manage it according to the best scientific evidence. If those data are
used against individual Contracting Parties, it is logic that national scientists cannot take this
individual responsibility. This is an old discussion, going on in various fora: as a general principle,
data from scientists should be used only for scientific purposes, while data from inspectors can be
used for compliance purposes. The risk in using the scientific data also for compliance purposes is
to face the situation SCRS is facing since years.
The second one is a perverted effect, because if Contracting Parties are not reporting the catch of
undersize fish, then it is very difficult to understand in which way the recruitment happens every
year, particularly when fishery independent research is not available. The fishery of juvenile bluefin
tuna is quite common in the Mediterranean since historical times. It is reported by ancient writers,
but it was considered a great problem also in the XVIII and XIX century: Avolio (1805) underlined
the need to protect the juvenile bluefin tunas and reported a royal decrees imposing the protection of
juveniles and the prohibition to catch, retain and sell them from September to December in 1795,
extended to March in 1796. ICCAT had set various measures to protect juvenile bluefin tunas, but
some of them were contradictory, allowing derogations for some fisheries, due to political
negotiations carried out at the Commission level. But the real problem was not only the catch of
juveniles by large vessels in some areas: it is the huge amount of small boats and vessels catching
juvenile bluefin tuna when they approach the coast to get the best food chain. As it was written in
several reports (Di Natale et al., 1986, 1987, 1988), small boats, mostly used for leisure fishery, are
able to catch important numbers of juveniles per day and the total number of these boats and vessels
in the Mediterranean Sea is quite huge.
Monitoring these catches is very difficult, because these fish are used for personal consumption or
for the local markets, but it is essential to understand the recruitment and follow the yearly
variations. If these data are not collected anymore of if they are not reported to SCRS for the risk of
compliance problems, then the SCRS has no tools to properly assess the recruitment, in the absence
of other indicators.
Figure 11 – An example of bluefin tuna weight frequency data collected by scientific observers in one area in
the Central Mediterranean Sea in 2008 (left) and the data as they are reported only by vessels having quota in
their landing declarations and in the official statistics for ICCAT Task II (right).
Figure 11 shows a true example of two data sets, collected exactly in the same area in 2008, one by
scientific observers monitoring the effective landing by all vessels and the other one as landings of
vessels having bluefin tuna quota reporting their catches in landing declarations and, then, in task II
statistics. This is happening since many years and in this way SCRS lost the opportunity mostly to
follow the high recruitment noticed in an anecdotic way by many scientists since 2003 almost in all
the Mediterranean areas, thanks to prolonged high temperatures at seas.
This lack of basic data on recruitment clearly negatively affected the result of the assessment,
independently from the tentative to apply correction factors under the hypothesis of various
recruitment scenarios.
Another trouble affecting the size distribution in the model is caused by the rare presence of large
fish. Usually, giant tunas are not abundant, because of natural factors, but their presence among the
catches in the Mediterranean fisheries was always reported in the past. In recent times, the number
of big fish in the national reports decreased and this was a further cause of concern in the SCRS
bluefin tuna assessment. Our Institute decided to pay a particular attention to this issue and it was
possible to identify several factors affecting the data. It is very clear that the different composition
of the bluefin tuna schools reported in the previous chapter was one of the causes, together with the
different fishing strategy of the purse seine fleet, but was not the only one. Giant bluefin tunas in
cages were present anyway and even very large specimens were identified (a few over 600 kg,
several over 400 kg and many over 200 kg). In the case of large fish, the effects of caging over the
fork length, independently from the number of months, is usually minimal, particularly if compared
to the same effect on juvenile tunas. These catches moved to cages were not properly monitored for
many years and these specimens often escaped from the statistics.
Figure 12 – An example of bluefin tuna weight frequency data from longliners collected by scientific
observers in two harbours in the Central Mediterranean Sea in 2008 (left) and the data from the same two
harbours as they are reported by vessel having bluefin tuna quota in their landing declarations and in the
official statistics for ICCAT Task II (right).
For gears other than the purse seine it was detected a different problem: due to the mandatory
logbooks and landing declarations, the only possibility for some fishermen to escape from a quota
overshot when landing in the authorised harbours was to lie about the weight of the individual fish,
because the number is always easy to check. Figure 12 clearly shows the effects of these actions on
the Task II data. This fact causes an important bias in the statistics, because of the decreasing
number of large fish, along with the disappearance of juveniles in the reports and together with the
higher presence of small and medium size fish. Logbook data from vessels having quota are used by
many CPs for their official catch declarations to ICCAT.
Length data used in the recent bluefin tuna assessment are affected by several other factors. One of
them is the poor correspondence between the real purse-seiners catches and the corresponding data
input in the VPA. As a matter of fact, after the adoption of the caging system, it become almost
impossible to get a proper number of length samples at the moment of catching the bluefin tuna,
before they are moved to the fattening cages. Only a few specimens die during the catch operations
or the transport and these are not considered as representative of the structure of the catch. To partly
overcome the problem, the ICCAT adopted Rec.06-07, making mandatory a sampling procedure at
the harvesting. This sampling, even considering various factors affecting the growth during the
different fattening periods, was considered able to provide more reliable information about the size
structure of the catches, particularly for the length frequencies of medium and large specimens,
where the growth in length is minimal when they are kept in cages for a few months.
During the last (2008) assessment, it was decided not to use these data, that were collected spending
a huge effort and an important amount of money by some CPs. At the same time, it was decided to
use the very few data concerning the fish died during the purse-seine catch operations (a little more
than 100 specimens) and raise them to the total catch, by using the Montecarlo suite of the VPA. It
is a common point of view of many scientists that this was able to create really a “virtual
population”, far from the real structure of the catches. It is very possible that this questionable
procedure was the causes of the lost of large specimens in the assessments, while very large
specimens were included in the length frequencies collected at the harvesting. The effect of this data
substitution on the assessment is unknown, but certainly was another contribution to the increasing
distance between the outlook and the reality.
Another issue is related to the CPUE series used in tuning the VPA. One of the most reliable for the
East Atlantic stock was the Japanese longline series, because the data are collected with a very
accurate methodology. This series showed a strong decreasing pattern and this was attributed at the
beginning to a clear sign of lower abundance of the stock. During the ICCAT/SCRS-GFCM
meeting hold in Genova (Italy) in 1996, it was clearly detected that the LL CPUE data for the
Japanese fleet operating in the Mediterranean were affected by the increasing number of fish stolen
from the LL by various fishing vessels7. This problem, able to seriously bias the analysis, was
described and agreed, but the data are still used without any correction factor and those contributes
in bringing down all the abundance estimates.
Total catch data, after the adoption of the quota system, faced a real disaster: it was possible for
several CPs to revise their catch statistics for the years previous to the adoption of the quota, which
were calculated on the 1995 and 1996 catches. Some CPs really tried their best to get the most
reliable statistics, recovering data from any possible source (including selling notes and invoices),
some others apparently revised their statistics without not so many references to specific
documents. The reason for that was to try to obtain the high possible portion of the quota, and this
was the real “gold rush”. Furthermore, the situation was complicated by the request to establish new
allocation criteria, not only considering the historical catches but also the new needs of coastal CPs,
even without any tradition in the bluefin tuna fishery. This new problem was based on the right of
each CP to access a distributed resource, which is justified in principle. The result of this exercise
was a further trouble in the system: CPs with a log historical tradition but with weak statistics got
quota shares that were insufficient to cover their fishing capacity, while others got quota shares that
were well above their fishing capacity. In a very few cases, vessel from the first set of CPs moved
to some CPs of the second group. The final result was that many CPs were suspected to underreport their total catch, some of them were officially identified by the ICCAT Compliance
Committee by cross checking the export data with the catch data, WWF submitted several reports
on this issue and SCRS tried to reassess the total figure of catch for the East Atlantic bluefin tuna
stock by using theoretical fishing capacity estimates, that were used in the assessment as a part of
the uncertainty and to develop various management scenarios.
7
The level of subtraction of bluefin tuna from the Japanese longlines was very high. It was possible to detect about 30
tons of stolen bluefin tuna in only one harbour in one single year.
SCRS, in all its reports since about 15 years stated very clearly that there was a progressive
deterioration of the data and, after the adoption of the quota system, that the data used for the
assessment were considered unreliable.
The final result of these and many other wrong or manipulated inputs to the VPA are now evident.
The last 2007 assessment, in its best scenario, reports a SSB of only 71,000 tons and a total biomass
ranging from 1 to 2 million bluefin tuna. These numbers are clearly very underestimated, because in
the same year the total estimated catch was around 61,000 tons and it is well known that each single
school of very small bluefin tuna (7-8 cm) can account to more than 100,000 individuals, while this
number change according to the individual size, and there are usually many hundreds of these
schools in each geographic area where there is the proper food chain. The very high number of
juveniles is also confirmed by the huge catch rate reported in the past for several small boats
illegally fishing for bluefin tuna. Even the catch of large specimens provides every years important
numbers. These data combined show that the current assessment provides, under the most
optimistic scenarios, total biomass and SSB which are clearly underestimated.
6
The request to move the Northern Bluefin Tuna, Thunnus thynnus (Linnaeus, 1758),
under the CITES Appendix 1
The proposal to include the Northern Bluefin Tuna (the West Atlantic and the East Atlantic stocks)
into the Appendix 1 of the Washington Convention (better known as CITES) was promoted by the
Government of Monaco in July 2009 and subsequently endorsed by various Countries, most of
them not concerned by the bluefin tuna fishery.
The proposal is mostly based on the low level of the actual bluefin tuna population, the
unsustainable level of fishing effort, the outputs of the assessment provided by SCRS with the
following low recovering figure of the population in the wild and the mismanagement of this fish
resource by ICCAT and all Countries concerned.
The proposal makes reference mostly to SCRS documents and WWF reports, but includes several
opinions that cannot be shared, because these appear politically addressed.
As a matter of fact, without considering the points raised in the previous chapters and many others
not here examined, it is possible for an external lecturer to agree in principle with the proposal, than
it is necessary to clarify some points and bring them under a more critical perspective, possibly
more close to the reality of the status of Atlantic bluefin tuna.
Besides some “minor” points, like the reduced spawning season reported or the small spawning
areas mentioned (which is really far from the scientific literature available), one of the key issue are
the outputs of the SCRS assessment in 2007, identifying a SSB of 72,000 tons and a total biomass
between 1,000,000 to 2,000,000 individuals. These estimates were already discussed at the end of
the previous chapter and they are clearly underestimated under the most optimistic projection.
Furthermore, in the proposal there is no mention of the SCRS report in 2006, when it was clearly
said that the data were unreliable and then SCRS was suggesting the ICCAT Commission to
postpone the assessment until reliable data will be made available. The big mistake by SCRS at that
time was to not resist to the Commission’s request to go on with the assessment as it was planned in
2007, without any care to this awareness sign. This is one of the most relevant issues in the entire
discussion, because an assessment carried out by using unreliable data cannot provide reliable
estimates, even exploring various scenarios and considering a wide range of uncertainties. Ignoring
this general unreliability is very relevant and an heavy responsibility.
The proposal by Monaco makes reference to a recent paper by MacKenzie et al. (2009). The
authors used very good mathematical models and their high skills but unreliable data sets and
academic hypothesis, quoting also papers (like Bearzi et al, 2006) which are based on non-scientific
methodologies8. There is the general opinion that the paper from MacKenzie et al. is a good
mathematical exercise, based on a high knowledge of population dynamics but without any direct
knowledge of the bluefin tuna itself and the fishery, possibly having a clear target to reach.
Bluefin tuna is considered in the Monaco proposal as “a medium productivity species”, while
usually bluefin tuna is included within the species having a considerable recruitment, which is the
case in the Mediterranean Sea since 2003. The natural mortality rate is assumed by convention since
many years and it is possibly underestimated, but it was adopted by SCRS and maintained the same
for a long period, without taking into account the improvements for the evaluation of this basic
factor, which is one of the most relevant in a population assessment.
The marked decline of the population reported by the proposal is logically and heavily affected by
the assumptions and the unreliable data; at least the SSB trend is clearly wrong (otherwise, we
should assume that the remaining less than 10% SSB in 2007 was able produce the high recruitment
noticed in 2008).
There is another factor affecting the overall view of the bluefin tuna spawning (and then the
recruitment capacity): the proposal from Monaco, along with a few other papers, reports data on the
spawning season and on the environmental conditions which are necessary to induce the spawning
that are wrong. As a matter of fact, it is well know by the huge scientific literature available that
spawning can usually occur from mid May to mid July, with certain variability according to the
local oceanographic conditions. The temperature in the upper stratum of the sea must be usually
>21°C (and not >24°C) and with a well established thermocline. This last factor is very relevant,
because it is necessary to have a certain water mass at the surface with the right temperature to
induce the biochemical stimuli and the proper temperature jump (usually a difference of about 3°C
between the upper and the lower stratum) at the thermocline to work as a sort of biological switch
for the spawners. Increasing the minimum temperature and shortening the spawning seasons (as it
was done in the proposal) are elements able to negatively affect the theoretic reproduction capacity
of the East Atlantic stock in the assessment.
The full vision of the status of Atlantic bluefin tuna is heavily negative, without considering several
factors, able at least to raise strong doubts about the pessimistic assessments, like, for example, this
point raised by SCRS in its 2008 report:
“In summary, available indicators from small fish fisheries in the Bay of Biscay did not show any
consistent trend since the mid-1970s. This result is not particularly surprising because of strong
inter-annual variation in year class strength. Indicators from longliners and traps targeting large
fish (spawners) in the East Atlantic and the Mediterranean Sea displayed a recent increase after a
general decline since the mid-1970s. The Group found it difficult to derive any clear conclusion
from fisheries indicators in the absence of more precise information about the catch composition,
effort and spatial distribution of the purse seine fisheries (which represent more than 60% of the
total recent reported catch). Fisheries-independent indicators and a large scale tagging program in
the Mediterranean Sea are also strongly needed to fill major gaps of scientific information.”
Another important point raised by the proposal is that the bluefin tuna is “affected by trade”: as a
matter of fact, the bluefin tuna is affected by international trade since the Roman times and maybe
even from the Phoenician times. Whenever we consider that the total catch level in the XVI century
8
The paper from Bearzi et al, 2006, pointing out the strong decreasing of bluefin tuna in the Ionian Sea, is based on an
assessment by “sightings of BFT” in a very small part of the Ionian Sea from an inflatable boat and for a couple of
years, applying the same methodology used for marine Mammals and without considering the fundamental behavioural
difference between a marine mammal and a fish! The same author, in a previous work, assessed the abundance of small
pelagic species in an island in Greece by counting the fish scales floating at the surface, collecting them with a small
net. This last assessment was taken as the scientific evidence to support the hypothesis of a food shortage for Tursiops
truncatus and then to request a IUCN specific status in the Red List.
in the Mediterranean was estimated to be close to 60,000 t (with tuna traps only)9, than we can
easily realise that there is something wrong in the present outlook and in the common understanding
of this species. Even the market motivations are wrongly stated, because fishery is not only driven
by the Japanese market and Mediterranean inhabitants do not consume only fresh tuna meat. Of
course, it is well known that many troubles were recently caused by the international trade,
particularly that one promoted by the Japanese market, and by the trade of IUU products, but these
are the results of weak controls, not by the trade itself.
The proposal by Monaco includes large parts of descriptions about the bluefin tuna natural history,
the biology and ethology, but there is a lot of misleading information. About recruitment, the effects
of environmental factors remain obscure, particularly if nobody analyse them. At the same time,
while it is well stated in the proposal that the ecological extinction of the bluefin tuna would result
in an unpredictable effect on the prey populations, it is simply not taken into account what was the
effect on bluefin tuna of the heavy fisheries on its prey species that is happening since decades. This
approach is scientifically not the most adequate. It is again a clear demonstration that the field
knowledge is very poor and the scientific literature considered is limited to the most recent papers,
independently from well established scientific knowledge.
A lot of attention is given to the fact that the bulk of the fishery is targeting spawners and this fact
heavily affected the SSB in the last 10 years. The problem is, again the poor knowledge of the
history of this fishery, because most of the historical catches over the centuries (at least in weight!)
have been always spawners, apparently without creating many troubles to the bluefin tuna
population. It is always a problem of balancing the catch with the availability of the resource and to
its components in age. When the proposal reports that ICCAT set quota levels well over those
indicated by the assessment, it doesn’t make any reference to the unreliable data used for it. Besides
of other considerations, this fact was taken into account by the Commission in assigning the quota
under a management plan.
If we consider as true the SCRS assessment, having between 25 to 35% overfishing of the MSY,
than it should be necessary to explain why, after more than 10 years of this situation, the bluefin
tuna is still alive and the purse seine fleets are able to catch about the full quota in less than 10 days!
It is clear, again, that the outlook is based on unreliable data and even less reliable assessments, as
stated many times by SCRS. This should be taken into account, together with the fact that bluefin
tuna (even if it is overfished at an unknown level) is still largely present in all the Mediterranean
Sea and in the Atlantic, while the enforcement of the ICCAT regulation is seriously becoming
effective and very strict measures were adopted by the EC in 200910.
The eventual suspension of bluefin tuna fishing mentioned by the ICCAT external advisory panel in
2008 (Hurry et al., 2008) does not necessarily include the listing of the stocks in CITES Appendix
1, but strict management measures; furthermore, it doesn’t take into account any social, cultural and
economic aspects of the fisheries. For example, the closure of the bluefin tuna fishery, even for only
one year, will result in loosing the tuna trap and the harpoon fisheries (two historical activities
having a very limited impact on the bluefin tuna stock) for ever, because they are not able to stay in
stand-by even for one year only. The harpoon fishery, targeting mostly swordfish, has the bluefin
9
This estimated level, obtained by extrapolating the known catch from several traps to the total number of the traps
known in the Mediterranean Sea, is very close to the maximum estimated catch obtained by SCRS for the East Atlantic
bluefin tuna stock in recent times.
10
The fishing season in 2009 was conducted with a 100% observers coverage of the EU purse seine fleet and 20%
observers coverage of the longline fleet, while many inspections have been conducted at sea by national and
international patrol vessels. The tuna cages in EU countries had 100% observers coverage. Many tuna vessels were
blocked at the harbours for compliance issues and the effective EU fleet was largely reduced. The purse-sine fishing
season was limited by bad weather situations, but vessel were able to catch the individual quota in a very short time, due
to the availability of the resource at sea.
tuna11 as an important component of its little economy and, without this species, it will be not
profitable anymore. The tuna trap fishery has a huge labour component and stopping the activity
even for only one year causes immediately losing the staff and a great economic damage for each
factory. Both of these fisheries are “survivors” from ancient times and a part of the Mediterranean
culture. Like for the traditional Inuit activities in whale fishing, at least historical fisheries should be
out of all these discussions and kept alive and active independently of any management decision.
It is useless to examine here in details all the other points of the proposal, because many parts are
more than questionable. Discussions should go on for long times and they usually happens every
year in SGRN.
7.
Conclusions
The poor knowledge of the natural history of this species by somebody is rapidly becoming science
in the public domain, forgetting about centuries of scientific papers. At the same time, it is clear that
the scientific information on this species and its fishery must be seriously improved, including the
necessary fishery independent data.
The CITES is a very important Convention, highly reputed all over the world, that was efficient and
effective in protecting many species from the extinction in the wild. All the species listed in
Appendix 1 have or had serious conservation problems in terms of threat of extinction and the
CITES is designed exactly for this. The CITES offices are used to deal with those problems and the
level of controls, fines and other legal provisions is very high in most of the signatory Countries.
This is the reason why the use of CITES for widely distributed species not having a real
conservation problem in terms of extinction is really inappropriate and pertaining to a political issue
more than a conservation problem. And nobody never demonstrated or even reported that the
Atlantic bluefin tuna is threatened by extinction.
Since years there is a clear mismanagement problem and the bluefin tuna is overfished, particularly
in the last years when fleets increased too much, but this is still a serious fishery management
problem and we are all lucky that it is not a conservation issue, because, again, bluefin tuna is not
threatened by extinction.
The unreliable and unrealistic outlook of the stock, caused by the unreliable data, and the
continuous shifting of the forecast (and the overfishing figure) after each assessment are all clear
indications that the situation is serious but it is not extremely dramatic. The unreliability of the data
and the outputs of the assessment make difficult to properly analise if the current situation of this
species fits the CITES criteria. When we take into account the situation at sea and many other issues
discussed in this paper, there is a good evidence of this statement.
Listing the Atlantic bluefin tuna in CITES Appendix 1 would result in practice in a complete ban of
the fishery in the Atlantic and the Mediterranean at least for the first two years and in very serious
and conflicting management issues in the following years, because the domestic CITES authorities
are different from the domestic Fishery authorities, and national CITES Scientific Commissions
usually do not include any fishery scientist.
CITES has an incredible amount of bureaucracy, maybe necessary to ensure a full control of the
system for very threatened species, but impossible to be followed by any fishermen and difficult to
be followed also by any Fishery authority. The time required by the CITES bureaucracy does not fit
any fishery need, because this Convention was established for other purposes.
Listing the Atlantic bluefin tuna in CITES Appendix 1 would possibly imply the immediate
extinction of the most historical traditional fishing activities in EU, like the tuna traps and the
11
Total bluefin tuna catches might be in the order of not more than 2 tons per year.
harpoon fishery, with a serious cultural and socio-economical problem. Both these activities have
no responsibility in the current troubles of the Atlantic bluefin tuna and they must be protected
anyway.
RFMOs and CITES have clear different management roles and different responsibilities (Di Natale,
2004a, Kell et al., 2000).
The Atlantic bluefin tuna has a serious management problem and even more serious data and
assessment problems, and these needs to be faced by the responsible management body, the
ICCAT, with the fundamental support of all the Contracting Parties and under the external overview
of important NGOs. This is a clear responsibility issue, but again not a conservation problem. The
bluefin tuna recovery plan must be immediately and strictly enforced, with no derogations or
exemptions.
If the management of Atlantic bluefin tuna will pass from the ICCAT, one of the most reputed
RFMO, to the CITES, than the credibility of ICCAT will be lost for ever and this will cause
unpredictable problems for many species and for the RFMOs system in general.
If the Atlantic bluefin tuna will be listed in CITES Appendix 1 having many millions of individuals
dispersed over the oceans, then the inclusion of many other halieutic species will necessarily follow
the same track in a short time, creating a serious problem in terms of management roles.
8.
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