4. The secrets of
tuna migration
Surprisingly, the migration patterns
of bluefin tuna within and outside
the Mediterranean Sea have not
been well studied. We have only
hypotheses and estimations.
Catches by traditional tuna traps in the Strait of Gibraltar
have indicated that some adult migration occurs from the
Atlantic Ocean to the Mediterranean basin between April
and May, and back out again to the Atlantic from July to
August8,9. Meanwhile, scientific studies of Atlantic bluefin
tuna in the Mediterranean Sea have indicated that key
spawning grounds of the species are located around the
Balearic Islands, Sicily, Malta, Cyprus10 and Libya11; that
spawning occurs during May-June in the east and June-
July in the central and western Mediterranean3; and that
there is genetic subdivision between the west and east
Mediterranean populations4. However, exact patterns
of migration from the Atlantic Ocean to the spawning
grounds, duration of stay within the Mediterranean,
and differences in migration patterns between juvenile
and adult tuna, between tuna inhabiting the western
and eastern Mediterranean, and even between tuna
within a single area of the sea, remain unknown.
6. On the Med tuna trail:
a pioneering tagging project
“Even though so little is understood
about the migratory behaviour of
Atlantic bluefin tuna, and therefore
how the fishery can best be managed,
the species is being chased to the
edge of extinction by a greedy spiral
of short-term business interests.
Through the project On the Med
tuna trail, WWF and its partners are
gathering essential new insights and
knowledge about bluefin tuna biology
– which, if used well by international
fisheries managers, can help keep
this magnificent species thriving in our
oceans for generations to come.”
Dr Sergi Tudela, Head of WWF Mediterranean Fisheries Programme
10. First “The migration
patterns of
By the end of the
second year of
the assessment of
the movements of a
results Atlantic bluefin
tuna in the
the project, some
interesting results
began to be seen.
wild tuna for an entire
12-month period, for
the first time ever in the
Mediterranean From the tags deployed Mediterranean. From
have never in 2008, all four pop- the tags deployed in
looked so ups detached from the 2009, five pop-ups
fish and transmitted (three from the coast of
interesting...” data via satellite after Roses and two from the
Dr Pablo Cermeño,
Tuna Tagging Coordinator, 60-125 days. One of Adriatic Sea) detached
WWF Mediterranean the 21 archival tags from the fish within 20
Fisheries Programme
was retrieved from days, which regrettably
a juvenile tuna after provided little
391 days – allowing information about the
The four adult Atlantic
bluefin tunas tagged
in mid-August 2008 off
the coast of Mallorca
stayed within a region
north of that island for
a period of at least
30 days. Three of
them then migrated
south-westwards from
this region, with their
tags detaching off the
south-eastern coast of
Spain and north coast
of Algeria between
mid-October and mid-
December 2008. The
fourth tuna remained
north of Mallorca for the
entire 70 days before
its tag detached at the
end of October 2008.
Figure 1 The four adult Atlantic bluefin tunas tagged in mid-August 2008 off the coast of Mallorca.
12. Figure 3 The two adult tunas tagged off the coast of San Benedetto del Tronto, central-eastern Italy.
Of the two adult tunas when its tag detached
tagged off the coast in late December 2009.
of San Benedetto del The other tuna traveled
Tronto, central-eastern steadily southwards
Italy, one stayed in for the entire 172 days
the Adriatic Sea for while its tag remained
the entire 103-day attached, crossing
period that its tag was the Ionian Sea and
attached, seeming to reaching the waters
spend more time in north of Libya when
deeper areas. It was its tag detached in
heading towards the early March 2010.
northern Adriatic Sea
15. Figure 5a The vertical profile of the juvenile Atlantic bluefin tuna Figure 5b The vertical profile of the same fish during a two-
during a two-day interval in summer 2009, while it was day interval in winter 2009, in the waters between
south of Mallorca in the Balearic Sea. Sicily and the eastern coast of Tunisia.
Why are these results significant?
On the Med tuna trail Results suggest that Mediterranean, giving of the ecology and
is the first ever study tuna use the waters more weight to the demography of
that has succeeded around the Balearic possibility that – again, bluefin tuna in the
in collating extensive Sea not only as a contrary to popular Mediterranean Sea.
information on the spawning ground, as belief – populations of With greater knowledge
possible migration has been believed the western and eastern of this unique species,
paths of Atlantic to date, but also as Mediterranean may not scientists will increase
bluefin tuna in the a suitable foraging frequently interact. their understanding of
Mediterranean Sea, ground. Furthermore, In view of these the population structure
using electronic tags. it appears that tuna preliminary findings, and dynamics of bluefin
Results obtained rely strongly on the and being aware tuna – and will thus
from the 2008 and topographical features that further research be able to give sound
2009 expeditions so of the sea bed in the is needed in order advice to fisheries
far suggest that both Adriatic Sea. There is to obtain definite managers (such as
adults and juveniles probably a link between conclusions, WWF ICCAT, the International
of the species in the the feeding area in remains convinced Commission for the
western and central the Adriatic Sea and that the novel results Conservation of Atlantic
Mediterranean spend the Libyan spawning of On the Med tuna Tunas) and legislators
more time exploiting grounds. Last, none of trail project so far of the Atlantic bluefin
the habitats of the the tagged individuals should be seen as a tuna population in the
Mediterranean basin to date ventured into first step towards a Mediterranean Sea.
than originally thought. waters of the eastern better understanding
16. Tuna tagging hits
the headlines
Spreading the word about
On the Med tuna trail
WWF has launched
From the outset, global media interest in WWF’s a special web section
tagging project On the Med tuna trail has been for On the Med tuna
trail. Follow project
high. The pioneering nature of the project,
developments online at
great images and colourful stories from the www.panda.org/
field have kept audiences hooked on news and tuna/tagging
developments. Press releases and media material
have been regularly drafted, translated and
shared with top journalists covering environmental WWF organizes press
trips on board the
issues around the world. Press conferences and WWF Columbus to allow
trips coinciding with launches and highlights top global media to
have also helped attract media attention, while experience tuna tagging
a specially designed interactive WWF website activities first hand
and learn more about
has provided an attractive information hub for a the purpose and aims
range of stakeholders. Raising visibility among key of the project. These
audiences is essential for the dissemination trips have resulted in
quality press coverage
of project results, and to ensure that ultimately
– including this TV and
the findings help make Atlantic bluefin tuna online reportage by
fisheries management more sustainable. Al Jazeera International.
On the Med tuna trail is in the global spotlight!
17. News and results from On the Med tuna trail splashed
across the media.
His Serene Highness Prince Albert II of Monaco, whose
charitable foundation has made the WWF project On the
Med tuna trail possible, has given generously of his own
time to help spread the word of the project and its wider
significance. HSH Prince Albert II granted an exclusive
interiew to Channel Four, the UK news network, on
board the WWF Columbus, which was broadcast in
prime time evening news programmes and online.