135 research outputs found
Report of the 2020 second intersessional meeting of the ICCAT bluefin tuna MSE Technical Group
Southward re-distribution of tropical tuna fisheries activity can be explained by technological and management change
There is broad evidence of climate change causing shifts in fish distribution worldwide, but less is known about the response of fisheries to these changes. Responses to climate-driven shifts in a fishery may be constrained by existing management or institutional arrangements and technological settings. In order to understand how fisheries are responding to ocean warming, we investigate purse seine fleets targeting tropical tunas in the east Atlantic Ocean using effort and sea surface temperature anomaly (SSTA) data from 1991 to 2017. An analysis of the spatial change in effort using a centre of gravity approach and empirical orthogonal functions is used to assess the spatiotemporal changes in effort anomalies and investigate links to SSTA. Both analyses indicate that effort shifts southward from the equator, while no clear pattern is seen northward from the equator. Random forest models show that while technology and institutional settings better explain total effort, SSTA is playing a role when explaining the spatiotemporal changes of effort, together with management and international agreements. These results show the potential of management to minimize the impacts of climate change on fisheries activity. Our results provide guidance for improved understanding about how climate, management and governance interact in tropical tuna fisheries, with methods that are replicable and transferable. Future actions should take into account all these elements in order to plan successful adaptation. © 2020 The Authors. Fish and Fisheries published by John Wiley & Sons Ltd.This research is supported by the project CLOCK, under the European
Horizon 2020 Program, ERC Starting Grant Agreement nº679812
funded by the European Research Council. It is also supported by the
Basque Government through the BERC 2018-2021 programme and
by the Spanish Ministry of Economy and Competitiveness MINECO
through the BC3 María de Maeztu excellence accreditation MDM-
2017-0714. We thank, without implicating, C. Palma for his helpful
advice on the ICCAT database and M. Gabantxo and H. Gabantxo for
their knowledge transfer about tropical tuna fisheries. Also, we thank
I. Arostegui for her comments during the design of the random forest;
F. Saborido, A. Tidd and H. Arrizabalaga for scientific advice and
H. Murua and M. Ortiz for providing ICCAT data. Elena Ojea thanks
the Xunta the Galicia GAIN Oportunius programme and Consellería
de Educación (Galicia, Spain) for additional financial support
Tracking bluefin tuna reproductive migration into the Mediterranean Sea with electronic pop-up satellite archival tags using two tagging procedures
Thirteen adult bluefin tuna were tracked with elec-
tronic pop-up satellite tags during their reproductive
migration towards Mediterranean spawning grounds as
they entered the Strait of Gibraltar. Fish were caught
in tuna traps and tagged either underwater, with the
aid of a modified spear gun, or on the deck of the boat.
Fish tagged on board initially showed a shallower
behavior than those tagged in the water. The pattern
of horizontal movements was also different between
both groups. Shortly after tagging, the eight fish tagged
in the water entered the Mediterranean Sea. Six of
these fish reached the spawning ground located south-
west of the Balearic archipelago before headin g back
for the Atlantic, whereas the other two traveled far-
ther east, reaching its easternmost longitudes between
Formentera and Sardinia and the South Tyrrhenian
Sea, respectively. In contrast, two out of the five fish
tagged on board never entered the Mediterranean Sea,
and another one did enter the Medi terranean when
the reproductive season was already over. These results
suggest an impact of the tagging procedure on the
post-release behavior of bluefin tuna. Exclu ding the
tags that popped-off east of the Strait of Gibra ltar,
bluefin tuna stayed in the Mediterranean Sea for 22–
28 days. Analysis of the median depth indicated a
shallow behavior during both day and nighttime
throughout the return phase of the fish from the
Mediterranean Sea to the Atlantic Ocean with the
exception of the area around the Strait of Gibraltar,
where they showed a deeper behavior that coincided
with a marked vertical gradient in the currents.Versión del editor2,044
Fidelity of yellowfin tuna to seamount and island foraging grounds in the central South Atlantic Ocean
The yellowfin tuna (Thunnus albacares) is a widely distributed, migratory species that supports valuable commercial fisheries throughout their range. Management of migratory species requires knowledge of movement, mixing and key life history parameters such as growth rate, natural and fisheries mortality. Current management is based on the assumptions that the species is highly migratory and populations are well mixed, but these assumptions have been questioned by recent studies. Since November 2015, yellowfin tuna have been tagged with conventional, archival and pop-up satellite tags (PSAT) in the South Atlantic Ocean around St Helena, with the goal of better understanding their movement patterns and ecology in this region. Conventional tags were attached to 4049 yellowfin tuna (size range 24–158 cm fork length, FL), PSAT tags were deployed on 15 yellowfin in inshore St Helena waters (size range 95–138 cm FL) and 7 yellowfin (size range 125–140 cm FL) at Cardno Seamount, and archival tags were deployed on 48 yellowfin tuna in inshore St Helena waters (size range 69–111 cm FL). Most yellowfin tuna remained within 70 km of their release location, suggesting a degree of retention to the region. Although displacement of yellowfin was generally low, the furthest distance travelled between release and recapture location was 2755 km, with other tuna also displaying large-scale movements. Tagging revealed connections between inshore regions and seamounts, as well as links between St Helena waters and key fishing regions and putative spawning grounds in the Gulf of Guinea
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