The Present State of Traps and Fisheries Research in the Strait of Gibraltar
The Strait of Gibraltar is defined as one of the most emblematic places in bluefin tuna biology, and the traps installed therein are platforms without equal in the study of this species. The enormous literature available on his fishing gear makes it impossible to make a full description from the historical point of view in the present study; however, some of the scientific activities and scientific committees of the last century are cited, followed by a list of the most recent research projects on the species. Two symposia, held in 2008 and 2011, dealing with bluefin tuna biology and fishing are reported, the latter of which was exclusively dedicated to the traps fishery and the research carried out at these fishing installations.
They are located approximately three kilometers from the coast and are more or less 34 meters deep, depending on each trap. The trap presents a complicated structure made up of a large skeleton of cables on which the nets rest, held to the bottom by means of lead weights and chains, and sustained by corks or floats in the upper part. It can be divided into two essential parts: the Catcher, mainly made up of the body of trap and the Auxiliary, which is the leader from shore to trap and the leader from offshore to trap.
Sella (1929), cited by Manfrin et al. (2012) first presented the existence of periodic fluctuations of 110 years in the fishing statistics of four traps of the Strait of Gibraltar and western Mediterranean Sea between 1770 and 1925. Rodríguez-Roda (1978) found periodic fluctuations in the catches of the traps in the south of Spain between 1929 and 1977 with maximums each 6 or 7 years. Later, in 2002, variability in the catches of eight traps in the eastern Atlantic and western Mediterranean between 1599 and 1960 was presented, revealing periodic fluctuations of 100–120 years that were inversely related to sea temperature, which may have led to variations in the migratory patterns of ABFT spawners in response to changes in oceanographic conditions (Frometin 2002).
According to Florido del Corral (2013): The establishment of Tuna Trap Fishing National Consortium (1928–1971) meant a commitment by the State, of a transformation of the enterprise and social organization of the Fishing Industry at the Andalusian Atlantic coasts (SW, Spain), confirming processes previously announced and inaugurating new ones. Business concentration, productive rationalization of manufacturing sites, and the consolidation of the company-towns crystallized in the central decades of 20th century, transforming traditional elements of the work cultures of the tuna fisheries, such as forms of retribution. These processes are better understood if we analyse them contextualised in the frame of power networks of the tuna fisheries oligarchy, which were characteristic in Andalusian and Spanish societies. From this holistic perspective, it is concluded the conflicting nature of the evolution of the tuna industry, between tradition and the productive rationalization.
While the Tuna Trap Fishing National Consortium was established (Ríos 2007; Florido del Corral 2013), a great deal of information was accumulated on the fishing activities and landing statistics Spanish traps, which were of great scientific value. Spanish scientists enjoyed the benefit of these advances to make their contribution to improving knowledge of tunas, mainly of ABFT.
The Spanish Civil War and the Second World War stalled the progress of non-war related scientific activities, but the end of these conflicts saw the beginning of great changes resulting from the need to find food originating from the sea for a population in great need.
International committees and working groups of the International Council for the Exploration of the Sea (ICES) already existed in those years (Hamre and Tiews 1963) and of the General Fisheries Commission for the Mediterranean (GFCM) (Lozano 1959) in which ABFT was studied by eminent scientists, such as Massimo Sella, Pascuale Arena and Raimondo Sarà (Italy), Fernando Frade and H. Vilela (Portugal), Henri Heldt (Tunisia-France), Jean Le Gall (France), Johanes Hamre (Norway), Klaus Tiews (Germany), Frank Mather III and Luis Rivas (U.S.A.), Akira Suda (Japan), and Julio Rodríguez-Roda and Fernando Lozano (Spain), among others.
Dr. Rodríguez-Roda retired at the beginning of the 1980s and since then scientists of the IEO have continued in their task, fulfilling the commitments acquired by Spain in the scientific research into this fishery. At first these were Juan C. Rey and Juan A. Camiñas, and later on José M. de la Serna, J. Ortiz de Urbina and D. Macías.
Reproduction and fecundity: Rodríguez-Roda (1967), Baglin (1982), Medina et al. (2002), Karakulak et al. (2004), Corriero et al. (2005), García et al. (2005), Heinish et al. (2014), Addis et al. (2016), Richardson et al. (2016).
Larvae and larval ecology: Piccinetti and Piccinetti Manfrin (1970), Dicenta and Piccinetti (1980), García et al. (2006), Alemany et al. (2010), Álvarez-Berastegui et al. (2014), Reglero et al. (2012), Laiz-Carrión et al. (2015).
Age and growth: Rodríguez-Roda (1964), Caddy et al. (1976), Butler et al. (1977), Compeán-Jiménez and Bard (1983), Cort (1990), Santamaria et al. (2003), Rodríguez-Marín et al. (2007), Restrepo et al. (2010), Cort et al. (2013, 2014, 2015), Luque et al. (2014), Ailloud et al. (2017).
Electronic tagging2: De Metrio et al. (2002), Block et al. (2005), Goñi et al. (2010), Wilson and Block (2009), Medina et al. (2011), Aranda et al. (2013), Lutcavage et al. (2013), Quílez-Badia et al. (2013), Cermeño et al. (2015), Galuardi et al. (2015), Abascal et al. (2016), Di Natale et al. (2016), Tensek et al. (2018).
In several published synopses (Mather III et al. 1973, 1995; Fromentin and Powers 2005; Rooker et al. 2007; ICCAT 2010) and numerous studies carried out in the field of ICCAT-GBYP Research, many more bibliographic references and published articles on the subjects cited and other can be found.
5.1 Chronology and Description of Two Symposiums and the ICCAT-GBYP Project
Soon after the implementation of PARP (2008) and when there were still no signs of the recovery of the eastern ABFT stock, the SCRS organized two symposiums that are going to be analysed since they are related to the traps fisheries.
5.1.1 World Symposium on Bluefin Tuna in Santander (2008)
The following is a literal transcription of some of the content of the report in ICCAT (2009).
The aim of the Symposium was to provide a deeper investigation of events that took place decades ago and to improve the understanding of these intriguing past events. This information should further help in improving current management and conservation measures for bluefin tuna fisheries.
The Symposium was a response to a recommendation of the Standing Committee on Research and Statistics (SCRS) in 2006.
Previous studies carried out within the framework of ICCAT have stressed the disappearance of some past fisheries or the drastic fall in the yields of others that generate changes in the spatial distribution of the catches.
Although these events occurred in past decades, they have marked the future of the fisheries. In the Atlantic, these events occurred in the 1960s, whereas in the Pacific, during the late 1800s and early 1900s, several fisheries that occurred in northern Japan suddenly disappeared, while more recently, several new fisheries have started in the Sea of Japan and coastal areas of northern Japan.
The Symposium was jointly organized by ICCAT and the Instituto Español de Oceanografía (Spanish Institute of Oceanography), IEO.
The IEO and ICCAT jointly organized the “World Symposium for the study of fluctuations in northern bluefin tuna (Thunnus thynnus and Thunnus orientalis), including historical periods”. At the event, which was held in Santander (Spain) between 22nd and 24th April 2008, 85 scientists from all over the world took part.
In 2007, the president of the SCRS, named a permanent committee made up of doctors J. M. Fromentin (France), J. Powers (U.S.A.) and N. Miyabe (Japan); this committee was coordinated by J. L. Cort (Spain).
The Symposium opened on April 22, 2008 with an official opening ceremony presided by Dr. Fabio Hazin, ICCAT Chair. Dr. Hazin thanked the Government of Cantabria and the city of Santander for hosting the meeting.
The ICCAT Chair emphasized the opportunity the Symposium presented at a time when the stock of North Atlantic bluefin tuna, particularly in the eastern Atlantic and Mediterranean Sea, was facing one of its worst crises in the history of the fishery. Dr. Hazin expressed the wish that the Symposium would help the SCRS to better assess the bluefin tuna stock and therefore contribute towards improving the management of the stocks.
Other scientific authorities of national and local administrations, as well as the municipal authority, spoke before the debate was opened.
The Symposium was organized in seven topical sessions coordinated by a moderator.
The present study only considers the sessions dedicated to Thunnus thynnus.
The documents of the symposium are available at ICCAT (2009).
22.214.171.124 Session 1: Historical Synthesis of the Bluefin Tuna Fisheries
SCRS/20108/058. Fonteneau, A. Atlantic bluefin tuna: An overview of 100 centuries of moving fisheries.
SCRS/2008/059. Fonteneau, A. and A. Le Person. Bluefin fishing in Lannion Bay, northern Brittany, during the 1946–1953 period.
Moderador: G. Scott (NOAA, U.S.A.)
Bluefin tuna fisheries have been identified in different areas of the Atlantic and Mediterranean over the last 10,000 years. Since the beginning of the XXth century these fisheries have undergone considerable industrial development.
The historical analysis confirms large-scale migrations and shows that bluefin tuna has been caught in a wide range of ecosystems between 2 and 29 °C, many changes being observed in where and when the species is caught. This fact is difficult to explain, although it would appear to be a combination of environmental and fisheries factors; exploring these more deeply will contribute to an improvement in the quality of assessments on the state of the stocks.
A practical example to orientate future studies regarding the previously mentioned spatial-temporal changes concerns the recreational fisheries of Northern Europe in the middle of the XXth century; such is the case of the fishery in Trebeurden Bay (British Channel), practiced between 1946 and 1953. This small fishery, associated with the presence of sardines in the area, provided a great deal of useful biological information related to the North Sea and Norwegian coastal bluefin tuna fisheries.
Our assessments of Atlantic bluefin stock status mainly focus on recent history, for which more detailed information is available about the catch, effort and size composition of the catch.
These assessments are uncertain, especially so regarding biomass levels that are necessary to meet the requirements of the ICCAT Convention.
Incorporation of more historical information could better inform us of stock productivity and abundance levels consistent with the ICCAT Convention objectives.
Our challenge will be to apply methods for stock status assessments that are more appropriate to the added complexities of the history we can piece together.
126.96.36.199 Session 2: The collapse of the North Sea and Norwegian Coastal Bluefin Tuna Fisheries
SCRS/2008/060. Tangen, M. The Norwegian fishery for Atlantic bluefin tuna.
SCRS/2008/061. Nøttestad, L., Ø. Tangen and S. Sundby. Norwegian fisheries since the early 1960s: What went wrong and what can we do?
SCRS/2008/062. MacKenzie, B. R. and R. A. Myers. The development of the northern European fishery for North Atlantic bluefin tuna, Thunnus thynnus, during 1900–1950.
Moderator: B. McKenzie (INRA, Denmark)
Speaker: L. Nøttestad (IMR, Norway)
Different descriptions of the ecosystem, before, during and after the disappearance of bluefin tuna from these fisheries, suggest that the collapse was not caused by great changes in water temperature, since bluefin tuna was present in times of high temperatures until 1960, and was also later caught in places where the temperature was as low as 3 ºC.
The coincidence of the collapse of herring stocks in the North Sea in the 1960s may explain the disappearance of medium-sized spawning bluefin tuna (<2 m) from these traditional fishing areas in the same years; large adults (>2 m) were still present even with a scarcity of herrings for a few more years until their complete disappearance at the beginning of the 1980s.The following causes are suggested that may have led to the absence of bluefin tuna in these fisheries:
Changes in migratory behavior,
Scarcity of adults in the population, and/or
The high exploitation of juveniles in other areas (Bay of Biscay, coasts of Portugal and Atlantic fisheries of Morocco).
On the other hand, the ideal conditions of the ecosystem since the 1990s with a great abundance of bluefin tuna prey including herring, mackerel and even anchovy, and optimal sea temperatures, leads to the conclusion that the fundamental reason behind the bluefin tuna’s disappearance and failure to return to these latitudes is the precarious condition of the population in the ocean.
The continual fall in spawning biomass over the last 10–12 years, which at its lowest point since the first records of ICCAT. The quantity of older fishes in the population has fallen,
The increase in the exploitation of juveniles since 1950. With an exploitation pattern in which 80–90% of fishes caught are aged 1–3 years (<30 kg), together with undeclared catches of age 0 fishes (<2 kg), a large part of the bluefin tunas recruited will never have the chance to reproduce.
The role of learning of migration patterns by young tuna from older tuna, and the necessity for overlap of spatial distributions of young and old tuna; the mechanisms by which learning is accomplished are unclear;
The possibility to acquire observational and occasional landings data via commercial and sport fishermen targeting other species and via whaling observers in northern European waters;
Possible links via migration to the population in the West Atlantic;
Attempts to estimate biomass in the early 1950s from age composition of catches and cohort identification;
Uncertainty of stock-recruit relationship;
The potential for individual tuna to skip spawning and subsequently to reduce fidelity to former spawning sites; and
The role of squid abundance and prey (especially herring) condition on bluefin tuna diets and condition.
188.8.131.52 Session 3: Decline of the Adult Fisheries of the Cantabrian Sea
SCRS/2008/063. Cort, J. L. The bluefin tuna (Thunnus thynnus) fishery in the Bay of Biscay.
SCRS/2008/064. Cort, J. L. and E. Rodríguez-Marín. The bluefin tuna (Thunnus thynnus) fishery in the Bay of Biscay. Evolution of 5+ group since 1970.
SCRS/2008/065. Cort, J. L., P. Abaunza and G. De Metrio. Analysis of the northeast Atlantic juvenile bluefin tuna (Thunnus thynnus) population between 1949 and 1960.
SCRS/2008/066. Rodríguez-Marín, E., J. M. Ortíz de Urbina, E. Alot, J. L. Cort, J. M. de la Serna, D. Macias, C. Rodríguez-Cabello, M. Ruiz and X. Valeiras. Following bluefin tuna cohorts from east Atlantic Spanish fisheries since the1980s.
Moderator: E. Rodríguez-Marín (IEO, Spain)
Speaker: J. L. Cort (IEO, Spain)
The fishery is traditionally made up of juveniles (1–4 years; between 4 and 35 kg). In the past there was a constant presence of medium-sized adults (up to 2 m) in the Bay of Biscay on the trophic migration from the spawning areas of the Mediterranean to feeding grounds in the North Sea. These groups have now practically disappeared from the fishery.
A sharp fall in the abundance of fishes aged 5+ (mean weight 62 kg) has been observed since the beginning of the 1970s in a fishery dominated by the catch of juveniles for the last three decades: 96.6% of the catch in number of fishes are juveniles.
The results of an analysis of the population of the Atlantic juvenile fisheries between 1949 and 1960 show that under different scenarios the high fishing mortality exerted during the years studied may have contributed to the fall in the spawning population of the eastern Atlantic and as a result been one of the causes of the decline in the fisheries of the north of Europe and the traps from 1963. The hypotheses that underlie the analysis show the existence of a certain degree of independence (“resident populations”) of eastern and western Mediterranean juvenile bluefin tunas based on recent studies using electronic pop-up tags.
The Symposium raised a number of research questions in the discussion of the presentations in Session 3:
To what degree did the development of fishing on the juvenile component of the stock from the 1950s to the 1970s influence the success of the catch of adults in the traps, in northern European waters, and the loss of age 5+ fish in the Bay of Biscay fishery?
The utility of strong annual year classes to establish relationships between fishing grounds?
It is important to know the contribution of recruits from the Mediterranean to the Atlantic fisheries:
Is there a wide variation in the proportion of fish leaving the Mediterranean?
Does this proportion have any relationship with density-dependent effects (competition for space and for food)?
As recovery rates in the Mediterranean are lower than in the east Atlantic, could this result in overestimating the number of Atlantic bluefin tuna leaving the Mediterranean?
What are the general trends in distribution and movements of the juvenile component that leaves the Mediterranean?
How important are learned behaviours and does the extirpation of abundances from other fishing grounds have strong implications in maintaining the presence of fish for the Bay of Biscay fisheries?
184.108.40.206 Session 4: Overall Vision of the Eastern Atlantic and Mediterranean Fisheries, Particularly the Traps
SCRS/2008/067. Fromentin, J. M. Back to the future: investigating historical data of bluefin tuna fisheries.
SCRS/2008/068. Abid, N. and M. Idrissi. Analysis of the Moroccan trap fishery targeting bluefin tuna (Thunnus thynnus) during the period 1986–2006.
SCRS/2008/069. Bridges, C. R., O. Krohn, M. Deflorio and G. De Metrio. Possible SST and NAO influences on the eastern bluefin tuna stock-the inexfish approach.
SCRS/2008/070. Karakulak, F. S. and I. K. Oray. Remarks on the fluctuations of bluefin tuna catches in Turkish waters.
SCRS/2008/071. Vella, A. Bluefin tuna (Thunnus thynnus) fisheries of the Maltese Islands in the central and southern Mediterranean Sea.
SCRS/2008/072. Addis, P., I. Locci and A. Cau. Anthropogenic impacts on the bluefin tuna (Thunnus thynnus) trap fishery of Sardinia (western Mediterranean).
Moderator-Speaker: J. M. Fromentin (IFREMER, France)
In 1963 the leading bluefin tuna fisheries, which took place in the Norwegian Sea and North Sea, suddenly collapsed without any warning. While little is known of the reasons underlying this collapse, several hypotheses can be put forward, e.g. changes in bluefin tuna migratory routes, recruitment failure or eradication of a sub-population (all three hypotheses may be due to natural causes and/or overfishing).
Current overexploitation in the Mediterranean Sea could explain why bluefin tuna did not return massively to the northeast Atlantic since the 1990s.
An analysis of the Moroccan tuna trap fishery targeting bluefin tuna, which shows that the CPUE generally decreased from 1986 to 1995, increased during the period 1996 to 2001, and has since shown a downward trend.
Historical data sets on catch and also model-generated data on spawning stock biomass (SSB) and recruitment have been used to look for possible influences of the North Atlantic oscillation (NAO) on the eastern bluefin tuna stock. Initial evidence has shown that total catch can be correlated to the winter NAO but only after a lag of two years.
Turkish trap fisheries for bluefin date back to the 15th century. Fish traps used to be set in the Sea of Marmara, Bosphorus and in the Black Sea from April/May to late August. With the fall in fish stocks, marine pollution and urbanization, fish traps lost their importance in the Turkish bluefin tuna fishery. Recent studies show that bluefin tunas have not been migrating to and from the Black Sea since 1986.
Traps in the Maltese Islands have caught bluefin tuna since 1748, reaching stable usage around 1948. However, this fishing method was finally replaced by longline.
The traditional traps of Sardinia harvest the ancestral migratory flow of the Atlantic bluefin tuna at a fixed site. Therefore, it is reasonable to consider local perturbations generated by social and economic events and environmental changes as disruptive to the pathways of bluefin tuna schools and thus account for variability in the Mediterranean trap captures.
There was a strong connection between the Nordic fisheries and the northeast Atlantic traps (from Spain, Portugal and Morocco) and secondarily with Mediterranean traps as well as the northwest Atlantic trap. The collapse of the Nordic fisheries is not an isolated event.
Atlantic bluefin tuna might be seen as a metapopulation made up of at least by three sub-populations that have varied in size in response to environmental changes and overfishing. Individual markers may be of great help to test the metapopulation hypothesis and thus the stock structure of bluefin tuna, as first results tend to show.
Fishing grounds also changed significantly in the eastern Mediterranean Sea during the 20th century, moving from the Marmara Sea to the Black Sea and finally to the Aegean. In general, there were several extinctions/discoveries of important fishing grounds in the Mediterranean as well as in the east Atlantic during the 20th century.
The importance of investigating fisheries on different spatial scales: i.e. large scales to detect connectivities between fisheries/stocks and impact of large-scale events (e.g. fishing, climate) and small-scale events to detect the impact of local events (e.g. coastal pollution due to industrial activities).
Traps provide highly valuable scientific information from an ecological and a fisheries perspective as they are a passive fishing gear being set at the same location and submitted to low technical modifications.
The causes of drastic changes in the fisheries of the 20th century are likely to result from interactions between biological, environmental, trophic and fishing processes.
220.127.116.11 Session 5: Overall Vision of the Western Atlantic Fisheries
SCRS/2008/073. Takeuchi, Y., K. Oshima and Z. Suzuki. Inference on the nature of Atlantic bluefin tuna off Brazil caught by the Japanese longline fishery around the early 1960s.
Moderator: J. Neilson (SABS, Canada)
Speaker: M. Lutcavage (UNH, U.S.A.)
The western Atlantic fisheries also had a long historical record and provided some landings information from the late 1800s for the New England fishery.
There is some evidence of a change in distribution to the northeast in the U.S. fishery. Possible reasons for the change could be related to prey distributions, and there have been observations of decreased condition of western bluefin tuna in the Gulf of Maine and southern Gulf of St. Lawrence.
Japanese longline fishery which appeared suddenly and virtually disappeared in about 10 years with a substantial catch around the early 1960s. Among several hypotheses that were proposed to explain this event the authors favoured the temporal distribution hypothesis (similar to the concept of metapopulation).
The western stock is in a low state of abundance, and the spatial distribution may be changing.
In common with the eastern stock, there are examples of tuna assemblages that have been extirpated. These have included large-scale aggregations, such as the one off Brazil in the 1960s, and smaller ones, such as the one that supported the trophy sport fishery off Nova Scotia (Sharpe Cup, 1930s–1960s).
PSAT tagging results show diversity of movement patterns; areas where bluefin have been extirpated would be expected to be periodically revisited, raising the potential for recolonization.
Changes in size structure can provide a warning of imminent fishery collapse.
18.104.22.168 General Discussion. Recommendations
Some important dynamics in Atlantic bluefin fisheries prior to 1970 should be incorporated into our overall analysis and utilized to shape our scientific advice to the Commission.
In the short-term (before the June 2008 stock assessment), it is unlikely that appropriate methodologies for incorporating historical information with different statistical characteristics into our stock assessment can be achieved to the full satisfaction of SCRS. This could only be achieved over a much longer period. While the current workplan for the 2008 bluefin stock assessment partly addresses the need to incorporate more biological realism into our evaluation of stock status, it is not clear that the current level of uncertainty in the assessment will be reduced in the short-run. Even in view of the high uncertainty, available information indicates that under recent conditions Atlantic bluefin tuna appear rapidly headed toward biological bankruptcy: spawning biomass is quickly shrinking and exploitation rates are much higher than the rate of interest nature provides. Our evaluations tell us that catches of bluefin tuna are now at their highest in ICCAT’s history; biomass of age 8 and older bluefin tuna is at the lowest level ever estimated and possibly the lowest since 1950 or before, and that these catches are much too high to permit the Convention objectives to be achieved. More historical information is likely to better inform us as to the biomass levels to which rebuilding must occur to be consistent with the Convention objective and the rate at which rebuilding can occur to meet the Convention objective, but it is less likely to greatly alter our assessment of current exploitation rates. Critical to the issue is seeking an answer to the question: can bluefin tuna abundance levels previously observed off the coast of Brazil, the North Sea and traps be re-established?
In view of the above, it is incumbent upon SCRS to fully describe the information needed to progress in improving the advice we can offer the Commission and how to obtain such information. This is likely to involve coordinated data collection mechanisms which, in general, have not yet been realized through the various national programs underway.
An important aspect of recovering historical information which can better inform our assessment of bluefin is a data mining activity designed to capture and incorporate historical information into the ICCAT database. It is of key importance that SCRS has full access to all historical fishery data collected on bluefin tuna, especially those from the early years of the 20th century. This data mining should, for instance, target the recovery of all the historical data collected (published and unpublished) on the North Sea fisheries (e.g. within the ICES Tuna Working Group on Norwegian, Swedish, German fisheries and from all other potential sources), from the various traps active in the Atlantic and the Mediterranean Sea and the various bluefin fisheries that have been active during the period but not recorded in the ICCAT database. Data mining efforts should also target the recovery of the various sport fisheries that targeted bluefin tunas in the Atlantic and Mediterranean during the 20th century (allowing the identification of the place and dates of positive activities and the CPUE and sizes of fishes caught by each of these sport fisheries).
The General Director of the IEO, Dr. Enrique Tortosa, thanked the participants for their attendance and for the excellent work carried out. Dr. Tortosa pointed out the current false paradox between the exploitation of fishing resources and the conservation of the species. He recognized the importance of the conclusions of the Symposium and the SCRS’ work to provide scientific advice. He further noted the relevance of the continued work of ICCAT in the adoption of measures for the management and conservation of the resources. The Director General of the IEO expressed the Spanish Government’s wish that public policies in general be based on science and that economy and resources be considered jointly.
Dr. José Luis Cort, the General Coordinator of the Symposium, thanked the participants for the exceptional work carried out. He recognized that the Symposium had represented an excellent forum for discussion on subjects that are rarely discussed in other fora and he judged very positively the discussions held and the conclusions reached.
The Symposium was adjourned on April 24, 2008.
5.1.2 ICCAT-GBYP Project
Improve basic data collection through data mining (including information from traps, observers, and VMS), developing methods to estimate sizes of fish caged, elaborating accurate CPUE indices for Mediterranean purse seine fleets, development of fisheries-independent information surveys and implementing a large scale scientific conventional tagging programme;
Improve understanding of key biological and ecological processes through electronic tagging experiments to determine habitat and migration routes, broad scale biological sampling of live fish and dead fish landed (e.g. gonads, liver, otoliths, spines, etc.), histological analyses to determine bluefin tuna reproductive state, biological and genetics analyses to investigate mixing and population structure; and ecological processes, including predator-prey relationships;
Improve assessment models and provision of scientific advice on stock status through improved modelling of key biological processes (including growth and stock-recruitment), further developing stock assessment models including mixing among areas, and developing and use of biologically realistic operating models for more rigorous management option testing.
During the Commission Meeting in 2009, a number of Contracting Parties expressed a willingness to make extra-budgetary contributions to such a programme with a view to initiating activities in 2009 related to different priorities: programme coordination, data mining, aerial surveys and tagging design studies; with additional research activities to be undertaken in the following years.
The provision to accept additional contributions from various entities and private institutions or companies was also agreed. In the same document, it was recommended to form a Steering Committee comprised by the SCRS Chair, the ICCAT Executive Secretary or his/her Assistant, bluefin tuna rapporteurs, and an outside expert with substantial experience in similar research undertakings for other tuna RFMOs, to guide and refine the Programme as necessary.
GBYP (Grand Bluefin Tuna Year Programme) was adopted as the official acronym of the research, which was initiated at the end of March 2010. It was divided in annual phases, sometimes covering parts of following years.
The project ICCAT-GBYP has meant and continues to mean the implementation of numerous scientific activities that contribute enormously to the knowledge of ABFT. These activities can be consulted under the tab ‘Research’ of the project web page.
Dr. Antonio Di Natale was the project coordinator between 2010 and 2018. Dr. Francisco Alemany took over from him in February 2018.
5.1.3 Symposium on Bluefin Tuna Traps Fisheries (ICCAT-GBYP 2011)
The following is a literal transcription of some of the contents of the report (ICCAT 2012).
The aim of the Symposium was to discuss and review the information from tuna traps to maximize the use of scientific information provided by this traditional gear. The Symposium should also provide the opportunity to improve knowledge and achieve a better understanding of this ancient fishery in order to find a common methodological approach to standardize the CPUEs related to this fishing activity, which has the longest historical series among all the world’s fisheries. Finding a common standardization procedure will allow these data series to be better used in the stock assessment models. Thus, this Symposium also represents an excellent opportunity to define the potential contribution of the trap fishery to the future work of the SCRS on the bluefin tuna stocks which should further help to improve the current management and conservation measures for bluefin tuna fisheries.
The Symposium was a response to a recommendation made by the Standing Committee on Research and Statistics (SCRS) in 2010 and was carried out within the framework of the ICCAT Atlantic-wide Research Program on Bluefin Tuna (GBYP).
The Symposium was open on May 23, 2011 by Dr. Pilar Pallarés, ICCAT Assistant Executive Secretary. Dr. Pallarés, on behalf of the Executive Secretary of ICCAT, thanked the Government of Morocco, the authorities of 4 Tangier and the National Institute of Marine Research for hosting the meeting, and welcomed the participants.
Dr. Pallarés made reference to the ICCAT Atlantic-wide Research Program on Bluefin Tuna (GBYP) within whose framework the Symposium was carried out and emphasized the importance of the trap fishery as a source of information on the history of bluefin tuna and its contribution to better understand the long-term dynamics of the population of this species. Dr. Pallarés expressed the wish that the Symposium will help the SCRS better assess the bluefin tuna stock and therefore contribute towards improving the management of the stocks.
Dr. José Luis Cort, Chair of the Symposium Scientific Committee, acted as Moderator for the Symposium. Dr. Cort acknowledged the kind support provided by the Moroccan tuna traps and the tuna industry for the organization of the Symposium and for hosting the official dinner. The Symposium was organized into four thematic sessions, each coordinated by a Moderator. The following participants acted as Moderators and Rapporteurs:
Session 1: A. Di Natale, M. Idrissi (ICCAT-GBYP)
Session 2: M. Ortiz (ICCAT)
Session 3: A. Fonteneau (IRD, France)
Session 4: Z. Suzuki (AFFRC, Japan).
A total of 58 scientists attended the Symposium.
The documents of the symposium are available at ICCAT (2012).
22.214.171.124 Session 1: Historical, Cultural and Technological Aspects of Bluefin Tuna Trap Fisheries
SCRS/2011/036. Di Natale, A. An iconography of tuna traps: Essential information for the understanding of the technological evolution of this ancient fishery.
SCRS/2011/078. Garcia Garcia, F. Las almadrabas de la costa andaluza bajo el dominio de la casa ducal de Medina Sidonia. Su tipología, sus producciones y sus problemáticas.
SCRS/2011/071. Gil Pereira, J. Historical bluefin tuna catches from southern Portugal traps.
SCRS/2011/083. Manfrin, G., Mangano, A., Piccinetti, C., Piccinetti, R. Les données sur la capture des thons par les madragues dans l’archive du Prof. M. Sella.
SCRS/2011/069. Farrugio, H. Données historiques sur les anciennes madragues françaises de Méditerranée.
SCRS/2011/081. Abid, N. Benchoucha, S., Belcaid, S., Lamtai, A. and El Fanichi, C. Moroccan tuna traps: History and current situation.
SCRS/2011/031. López González, J.A., Ruiz Acevedo, J.M. Series históricas de capturas del bluefin tuna en las almadrabas del Golfo de Cádiz (Siglos XVI-XXI).
SCRS/2011/037. Di Natale, A. Literature on the eastern Atlantic and Mediterranean tuna trap fishery.
The discussion examined the fact that not all the Mediterranean areas are documented in the same way and the reason for that possibly reflects the fact that the trap fishery was perhaps not practiced in some east Mediterranean countries. Some data were provided in the 13th century by the famous geographer El Idrissi. It was noted that the detailed archives of the Ottoman Empire have not yet been analysed. The discussion also included historical information on the impact of killer whales on the fishery in the Strait of Gibraltar, the socioeconomic importance of the direct and indirect income derived from the tuna trap industry and the effects of having a series of tuna traps along the same coast. The high catches in the historical series are understandable, but it is more difficult to understand the reasons for the low catches. The mixture of species that are reported in the historical Duke of Medina Sidonia series will require additional data mining for further study. The conclusion of the session stressed the relevant importance of tuna traps from a cultural, historical and social point of view and the need to preserve this activity for the future. It was noted that historical data on trap fisheries require the identification of size classes, common names, size-class category, possible different species composition and market categories recorded, before combining multiple sets of data for these analyses.
126.96.36.199 Session 2: Bluefin Tuna Trap Data and Standardization for Assessment Uses
SCRS/2011/039. Ortiz, M., Palma, C., Pallarés, P., Kell, L., Idrissi, M. and Di Natale, A. Tuna trap data existing in the ICCAT database and data recovered under the GBYP.
SCRS/2011/028. Cort, J.L., de la Serna, J. M. and Velasco, M. Annual mean weight of bluefin tuna (Thunnus thynnus) caught by the traps in the south of Spain between 1914–2010.
SCRS/2011/038. Di Natale, A. and Idrissi, M. Factors to be taken into account for a correct reading of tuna trap catch series.
SCRS/2011/027. Abid, N., de la Serna, J. M., Rodriguez Marín, E., Macías, D., Rioja, P., Ortiz de Urbina, J.M. Standardized CPUE of bluefin tuna (Thunnus thynnus) caught by Moroccan and Spanish traps for the period 1981–2009.
SCRS/2011/041. Kai, M. and Takeuchi, Y. Abundance index of young Pacific bluefin tuna (Thunnus orientalis) estimated from the Japanese set net fishery’s data.
The general discussion commented on the importance of the trap fisheries as a major source of scientific and fisheries data for the assessment of bluefin tuna stocks and the need to continue supporting the scientific collection and reporting of data from trap operations. It was noted that management measures, such as quota restrictions, need to be taken into account for data collection and data analysis. Therefore, there is a need to record retained as well as released fish from traps, and to have standard descriptions of fishing operations to define clearly the fishing effort unit. In addition to the CPUE series from trap catches, size and age distribution samples should be routinely collected. Analyses from traps in southern Spain have shown the change in the trends of size and age of fish caught among various series of years. In such cases it is recommended that the CPUE series be standardized by age or age-groups for the assessment process. It was also recommended that analyses of trap fishery data be carried out on a wider regional scale, including coordination of the potential links between overall environmental trends (currents, decadal oscillations, etc.).
It is also important to understand the effects of small scale meteorological events on the catch rates of local traps.
188.8.131.52 Session 3: Tuna Traps as a Reliable Scientific Observatory for Bluefin Tuna Stocks
SCRS/2011/075. Addis, P., Secci, M., Locci, I., Sabatini, A., Dean, J. M. and Cau, A. Long-term analysis (1993–2010) of the catches of Atlantic bluefin tuna (Thunnus thynnus) from the traditional trap fisheries of Sardinia.
SCRS/2011/0074. Dean, J. M., Andrushchenko, I. and Neilson, J. D.The western Atlantic bluefin tuna trapnet fishery.
SCRS/2011/042. Suzuki, Z. and Kai, M. Movement of Atlantic bluefin tuna toward the Strait of Gibraltar inferred from Japanese longline data.
SCRS/2011/029. De la Serna, J. M., Macías, D., Ortiz de Urbina, J. M., Rodríguez-Marín, E., Abascal, F. Study on the eastern Atlantic and Mediterranean bluefin tuna stock using the Spanish traps as scientific observatories.
SCRS/2011/084. Fonteneau, A. Mediterranean traps in the 21st century: Research tools for the conservation of bluefin tuna.
SCRS/2011/080. Cannas, R., Ferrara, G., Milano, I., Landi, M., Cariani, A., Addis, P., Cau, A., Piccinetti, C., Sella, M., Tinti, F. Spatio-temporal genetic variation of Atlantic bluefin tunas from Sardinian and Mediterranean tuna traps.
The general conclusion following these presentations and the discussion was a firm consensus that for ICCAT scientists bluefin tuna traps were for four centuries, and remain today, an invaluable gold-mine of data (statistical, biological and others), while recent fishing mortality due to tuna traps is low and the sizes of bluefin tuna caught by the traps is close to the optimum in terms of yield per recruit. On the other hand, ICCAT scientists recognize that the statistical and scientific information obtained from modern and recent gears (such as purse seiners) is and has been extremely limited, particularly for a period during which these modern gears have been the major source of excessive fishing mortality suffered by the bluefin tuna stock.
In this context, these data from traps are as essential today as they were in the past for ICCAT bluefin tuna stock assessment, because they provide age-specific measures of stock biomass for both the sedentary and migrating fraction of the bluefin tuna stock, and also a wide range of biological data that constitute a very important component in the bluefin tuna stock assessment models.
There is a consensus among scientists that it would be very negative to stop now, after 400 years of continuous data, these unique statistical series from the trap fisheries. The recommendation from this Symposium to the ICCAT Commission and to the ICCAT CPCs is to maintain the trap fisheries operational, inter alia because of their high value for scientific research and stock assessment. The Symposium participants also recommended that these traps should be kept open for a period that allows the continuation of their long-term statistical series.
It is also recommended that these traps be considered as “ICCAT tuna observatories”, increasing their cooperation with ICCAT and its scientific programs by providing full access to their detailed catch and effort data, giving access to biological sampling and allowing the tag and release of bluefin tunas.
184.108.40.206 Session 4: Tuna Traps and Bluefin Tuna: Socio-Economy, Global Management and Market Issues
SCRS/2011/040. Suzuki, Z., Kai, M. General information on Japanese trap fisheries catching Pacific bluefin tuna (Thunnus orientalis): Fishery and socio-economic roles.
SCRS/2011/082. Malouli Idrissi, M., Zahraoui, M. Nhhala, H. Les madragues au Maroc: Aspects économiques.
SCRS/2011/076. Addis, P., Secci, M., Locci, I., Cannas, R., Greco, G., Dean, J. M., Cau, A. Social, cultural and basic economic analysis of the trap fishery of Sardinia: First step towards parameterization.
SCRS/2011/077. Addiss, P., Secci, M., Locci, I. Cau, A. Harvesting, handling practices and processing of bluefin tuna captured in the trap fishery: Possible effects on the flesh quality.
Discussions centred on the following:
As concerns the Japanese trap presentation, it was asked whether or not the Japanese government gave preferential treatment to traditional fisheries such as the traps with respect to management of the stock. The answer was that it did not give any special treatment to the traditional fisheries but there appeared to be general agreement that the traditional fisheries should be less affected by the regulatory measures because their fisheries had been sustainably conducted.
Clarification was made to the fact that fuel cost is a dominant item of expenditure in the Moroccan trap fishery and it was explained that the reason for the high fuel cost in total expenditure was due to the long distance between the ports and trap locations and to the trap setting-up operations, which require considerable time and effort.
Some concern was raised about using the “matanza” (killing of bluefin in the final stage of trap harvest) as a tourist attraction. Although there were no complaints from the tourists who watched the “matanza”, it may be necessary for persons in charge of the trap fishery to be prepared to give an explanation of this activity.
A question was raised about the cooperation among trap owners and scientists who collect biological samples and the response was that most of the sampling is permitted although it depends to a large extent on the kind of samples taken. It was noted that maintaining a good relationship with the industry is important and this may be done through feedback to the industry from the scientific research results obtained by biological sampling. It was agreed that the proposals made by the tuna trap industry be included as Appendix 3 of the report in a summarized format.
The historical data series from the tuna trap fishery archives that have been recovered in the last two years provide an important improvement to the ICCAT data base. The Symposium recommends that further details be made available by national scientists for a better understanding of the natural fluctuations of the stock and to improve standardised CPUEs taking into account the most relevant variables.
The considerable historical and cultural importance of the tuna trap fishery and industry shall be preserved. The Symposium recommends that the national governments concerned take the necessary steps to promote the urgent conservation of the few remaining tuna traps by considering, among others, the possibility of requesting their inclusion under “World Cultural Heritage” by UNESCO.
It is also recommended that these traps be considered as “ICCAT Tuna Observatories” by increasing their full cooperation with ICCAT and its scientific programs, providing full access to their detailed catch and effort data, permitting biological sampling to be carried out, and by allowing the tag and release of bluefin tunas.
For the opportunity to effectively use the tuna traps as “Tuna Scientific Observatories” the Symposium reiterates the recommendation from the SCRS in 2010 to the Commission to establish a scientific quota allocation for the ICCAT Atlantic-Wide Research Program on Bluefin Tuna (GBYP). This allocation should not fall under the restrictions of current size regulations and should include all fish-size ranges.
For standardizing the CPUE series from trap fisheries, it is recommended that:
Records be kept of landed fish as well as fish released from the traps.
Records be kept of size and/or age information of the fish caught, and indices be developed by age or age groups if there are changes in the size distribution of fish caught in the traps.
Regional-wide studies be promoted on the trends of catch rates at size-age from different tuna traps.
There is a consensus among scientists that it would be very negative to stop now, following 400 years of continuous data, these unique statistical series from the trap fisheries. The recommendation from this Symposium to the Commission and to the ICCAT CPCs is to maintain the trap fisheries operational, inter alia, because of their high value to scientific research and stock assessment.
The Symposium participants also recommended that these traps be kept open for a time period long enough to maintain the consistency of their long-term statistical series.
220.127.116.11 Adoption of the Report and Closure
Dr. José Luis Cort, the Moderator of the Symposium, thanked the participants for the exceptional work carried out and expressed special appreciation to the Secretariat and, in particular, to the GBYP for the excellent organization of the Symposium.
The report of the Symposium was adopted. The Symposium was adjourned on May 25, 2011.
Following this general presentation of ABFT and its fishing, the aim of the present article is to study the Bay of Biscay fishery in detail. This fishery is one of those that has been the subject of the largest number of studies and the authors of the present paper have recently published a study on it (Cort and Abaunza, 2015) describing the interaction of the fishery with the other spawner fisheries in the eastern Atlantic.
The internal electronic tags (archival tags) are small computers that are placed in the peritoneal cavity of the ABFT, which record dates, times, fish depths, water temperature, body temperature and light levels, which are used to calculate an approximate daily position of the tagged animal depending on the times of dawn and dusk and the angle of the sun. To download the data the fish must be recovered. The electronic tags can record data every few seconds over several years depending on the tag´s sampling frequency and the duration of the battery.
The electronic pop-up tags, also known as PAT satellite tags, compile information on oceanic movements and preferred water temperature, clarity and currents through GPS location technology. They are pre-configured to come loose at a programmed time and rise to the surface to transmit the data to the Argos satellite network. This network collects, processes and disseminates environmental data and has a special channel dedicated to wildlife telemetry.
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