• José Luis CortEmail author
  • Pablo Abaunza
Open Access
Part of the SpringerBriefs in Biology book series (BRIEFSBIOL)


A brief description is made of the Atlantic bluefin tuna, Thunnus thynnus (L.), from the point of view of its biology, geographic distribution and population dynamic. With the Strait of Gibraltar traps as a reference and providing a vision from ancient times to the present, scientific activities on this fishing gear are reviewed in an attempt to explain the reasons behind the crisis of the catches in this fishery, which began at the beginning of the 1960s and which has been extended until recent times. In order to do so and based on a recent publication on the issue, the Bay of Biscay fishery is presented as a fishery with a long tradition on which numerous scientific studies have been carried out and whose data are of great importance in the ABFT assessment group of SCRS (ICCAT’s scientific committee). Traditionally, the catches of this fishery have been made up of juvenile specimens (<40 kg) making up more than 97% in number of fishes according to a 62 year series studied (1949–2010). From an analysis of the population it has been shown that the impact of massive fishing of juveniles in this fishery between 1949 and 1962, together with that of juveniles in Morocco (the Atlantic part) possibly caused the decline of the traditional traps fishery of spawners in the Strait of Gibraltar and the collapse of the spawner fisheries in the north of Europe from the 1960s. This situation continued until 2007, the year from which a Pluri-Annual Recovery Plan (PARP) was adopted by ICCAT for the eastern stock. Since the PARP was implemented juvenile catches have disappeared from almost all the fisheries, a scenario that coincides with a considerable recovery of the spawning stock biomass in the eastern eastern Atlantic and Mediterranean, according to the results of the latest SCRS assessments.

Atlantic bluefin tuna, Thunnus thynnus (L.), from the Atlantic and Mediterranean, hereinafter referred to as ABFT, has undergone various crises in recent times owing to overfishing, which is why the International Commission for the Conservation of Atlantic Tunas (ICCAT) recently adopted highly restrictive conservation measures for the protection of the resource. The ICCAT Standing Committee on Research and Statistics (SCRS) carries out periodic assessments of resources to examine the impact of such conservation measures on the population.

Since the middle of the 20th century fishing pressure on ABFT resources has been growing constantly, causing increasing damage to stocks. New fisheries have been created and fishing effort has increased throughout the Atlantic and Mediterranean to the extent that on two occasions, one in 1993 (Safina 1993) and the other in 2009 (Fromentin et al. 2014) the species’ inclusion under Appendix 1 of the Convention of International Trade in Endangered Species of Wild Fauna and Flora (CITES) was proposed. Were it to be included it would mean the prohibition of international trade in ABFT. This did not happen on those two occasions, but it was a close call. ICCAT’s intervention was crucial on both occasions in redirecting the situation and returning the resource to a situation of apparent sustainability.

Among the most relevant events in recent decades the following can be highlighted:
  • Overfishing in the eastern Atlantic in the 1960s (when ICCAT had not yet been founded), which led to a permanent crisis in the traps fishery of the Strait of Gibraltar and the collapse of the northern European fisheries (Cort and Abaunza 2015). From the 1970s purse seine fishing developed rapidly in the Mediterranean, which became the main fishing gear for the catch of ABFT in this sea (ICCAT 2010). Meanwhile, the spawner fisheries of the eastern Atlantic remained at very low levels from the beginning of the 1960s and in 1974 led ICCAT to adopt the first conservation measure (ICCAT 1974), which established a minimum catchable length of age 1 fishes (W = 6.4 kg). This measure was not implemented in any eastern stock fisheries until the beginning of the 2000s, which for decades resulted in the illegal catch of millions fishes below the minimum length.

  • At the beginning of the 1980s a second ABFT crisis arose as a result of overfishing, this time in the fisheries of the western stock (a definition of a stock is provided later), a crisis that led to ICCAT’s adoption of the first TACs (Total Allowable Catches) for this species, which have been set between 2000 and 2500 t/year since 1982 (Fromentin and Powers 2005). Later, following the recent disappearance of traditional fisheries such as the Sicilian traps, the continued proliferation of purse seine fleets in the Mediterranean and illegal fishing by vessels with flags of convenience had taken ABFT catches to an official figure of 50,000 t in 1995 (ICCAT 2014; Fromentin et al. 2014), in 1998 ICCAT adopted the first TACs for the eastern stock fisheries (32,000 t/year), though the quantity recommended by the scientists at that time was between 15,000 and 25,000 t/year. Nevertheless, following the adoption of this conservation measure there was a complete lack of monitoring among the fleets and the measure was only implemented in the traps.

  • Lastly, the Mediterranean overfishing in the 2000s coincided with the start of purse seine fishing for fattening on farms, an activity that brought about the plundering of the species in the Mediterranean (WWF 2008). According to estimations made by the SCRS, the real catch between 1998 and 2006 was between 50,000–61,000 t/year, though the TAC remained at 32,000 t (Fromentin et al. 2014). The scientific reports of 2008 and 2010 pointed to a fall in the spawning biomass of up to 80% below that of the maximum sustainable yield (ICCAT 2012; ICCAT 2014). In view of all this, in 2007 ICCAT adopted a Pluri-Annual Recovery Plan (PARP) throughout all the fisheries of the eastern Atlantic and Mediterranean (ICCAT 2006) involving a very low TAC (for example, 12,900 t in 2012) among other measures such as limiting the minimum weight at catch to 30 kg (ages 1–4), all under the management of the international commission. There were, however, some exceptions to the minimum weight, such as in the Bay of Biscay, Adriatic Sea and the artisanal coastal Mediterranean fishery, where it is just 8 kg (ICCAT 2007).

The PARP has important consequences:

(i) It has led to a considerable reduction in the TAC, which has in turn led to a large fall in the number of fishing vessels in the Mediterranean; (ii) the increase in the minimum size of ABFT (from 10 to 30 kg) has brought about the disappearance of most of the juvenile fisheries; and (iii) it has brought with it strict monitoring of the landings of this species. All of this has meant that in the ten years that the PARP has been in force the spawning stock biomass of ABFT has increased very significantly, something to which the high recruitments in some years may have contributed as a result of favorable environmental conditions (Piccinetti et al. 2013). In the most recent assessments (ICCAT 2012, 2014, 2017) and from different fishing indicators available to the assessment group [the traps in Sardinia (Addis et al. 2012); the Moroccan traps of the Atlantic (Abid et al. 2017); the larvae of the Balearic Sea (Álvarez-Berastegui et al. 2018); the Spanish purse seiners in the Balearic Sea (Gordoa 2014, 2017); the Portuguese traps in the Strait of Gibraltar (Lino et al. 2018); the Japanese long liners in the Atlantic (Kimoto and Itoh 2017); the aerial surveys in the Gulf of Lion (Rouyer et al. 2018); and the Tunisian purse seiners in the central Mediterranean (Zarrad and Missaoui 2017)] a very considerable recovery of resources has been recorded, which has given rise to a continual increase in quotas (TAC = 36,000 t by 2020) which may bring the PARP to an end.

Since the very first fishing season following the implementation of the PARP (2008), a minimum of 840,000 juvenile specimens (<30 kg) were no longer being caught each year in the central and western Mediterranean (Cort and Martinez 2010). This figure is mainly based on the catches of the 83 vessels of Italy, France and Spain (>40 m) registered at ICCAT, which caught around 100–150 t/year of juveniles according to estimates made by the SCRS (ICCAT 2008). Most of these juveniles have now joined the spawning stock and this is possibly one of the reasons behind the continuing rise of the abundance indices of spawners since then. A simulation made by Belda and Cort (2011) in a scenario in which there were no juvenile catches (<30 kg) by the EU fleet reveals the same trend and quantity of biomass as that reached in the assessment of the ABFT group in 2017 (ICCAT 2017).

Since the adoption and implementation of the PARP the situation has been completely turned around, such that now, under the monitoring of fisheries by member states, the resources of this species are very much recovered (ICCAT 2014, 2017). Moreover, scientific activities on ABFT have since multiplied (Di Natale et al. 2018).

The present study focuses on one of the events described above: overfishing in the 1950s, which was what brought about the disappearance of most of the traps of the Strait of Gibraltar and led to the collapse of the northern European fisheries from the 1960s; the answers provided by science concerning these facts; how the catches of the juvenile fisheries affected this crisis; and how the crisis in catches has now been overcome.

To deal with this matter, and considering the traps as a central theme of the study, the following chapters are described:
  • A brief review of the ABFT, which includes some characteristics such as the description of the species, its habitat, stocks, migrations, growth, reproduction, fishing, etc.

  • The catch of the species, taking into account the traps of the Strait of Gibraltar, making a tour from their ancient history to the present. This section includes accounts based on archaeological research in the Strait of Gibraltar.

  • The trap fisheries from a historical point of view, though given the immense bibliography on this subject and the numerous scientists involved in it, scientific activities related to this fishing gear by Spanish scientists from the twentieth century are cited.

  • ABFT fisheries in the eastern Atlantic, the interaction among them and associated research. Special attention is paid to the Bay of Biscay fishery, both from the historical point of view and from fisheries research, as this is now one of the most closely studied ABFT fisheries.

  • The latest assessments of ABFT resources carried out by the SCRS group of experts, the most important scientific reference regarding the situation of the stocks of this species.


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Authors and Affiliations

  1. 1.Centro Oceanográfico de SantanderSpanish Institute of OceanographySantanderSpain
  2. 2.Spanish Institute of OceanographyMadridSpain

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