Unusual Association of Skipjack Tunas Katsuwonus pelamis and a Longline Vessel

Abstract

Skipjack tuna were observed for the first time swimming in front of the bow of a fishing vessel during a tagging campaign in the North Atlantic. Video recordings show how tuna adapted their speed and direction to the vessel, using the pectoral fins to move from top to bottom and back and forth across the bow of the ship. We discuss the potential drivers of this behaviour.

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Journal : Large 12601 Article No : 2Pages : 3MS Code : 2Dispatch : 22-3-2021
Vol.:(0123456789)
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Ocean Science Journal
https://doi.org/10.1007/s12601-021-00002-6
NOTE
Unusual Association ofSkipjack Tunas Katsuwonus pelamis
andaLongline Vessel
GonzaloMucientes1,2,3· NairVilas-Arrondo4
Received: 24 July 2020 / Revised: 1 September 2020 / Accepted: 1 September 2020
© Korea Institute of Ocean Science & Technology (KIOST) and the Korean Society of Oceanography (KSO) and Springer Nature B.V. 2021
Abstract
Skipjack tuna were observed for the first time swimming in front of the bow of a fishing vessel during a tagging campaign in
the North Atlantic. Video recordings show how tuna adapted their speed and direction to the vessel, using the pectoral fins
to move from top to bottom and back and forth across the bow of the ship. We discuss the potential drivers of this behaviour.
Keywords Tuna association· Behaviour· Katsuwonus pelamis· North Atlantic· Fishing vessel· Interaction
1 Introduction
The skipjack tuna, Katsuwonus pelamis (Linnaeus 1758)
is a medium-sized tuna species with a wide distribution in
the Atlantic Ocean. It is a short-lived species that matures
at ~ 2 years and 45–48cm (Hazin etal. 2001). It feeds on
fishes, crustaceans, cephalopods and molluscs, but, canni-
balism has also been reported (Hart 1973). Large schools of
skipjack tuna have been observed in the open ocean. Tuna
schools confer important advantages to the individuals such
as predator avoidance, cooperative hunting or resting (Godin
1997). In fact, many species of tunas aggregate under float-
ing objects and fishers take advantage of this behaviour by
deploying fishing aggregation devices (FADs) that attract
fish (Dagorn etal. 2007). Schools of skipjack tuna have
also been observed in surface waters with dolphins, birds,
sharks, whales, while performing characteristic behaviours
like jumping, feeding or foaming (Hall 1992) but also as
free-swimming schools not associated with either dolphins
or floating objects. The objective of the present work is
to report and describe unusual behaviour of skipjack tuna
observed in relation to a fishing vessel and discuss similar
behaviours across several species.
2 Materials andMethods
During a tagging survey for pelagic sharks conducted in
September 2011 off the Azores islands, North Atlantic
(location 35°N and 38°W), unusual swimming behaviour
in association with a fishing vessel was observed from the
boat deck. The observations were recorded with a compact-
camera Sony Cyber-Shot G and GoPro Hero 3 (in time lapse
mode) attached to a pole, in good weather conditions and sea
surface temperature of 26.5°C.
3 Results andDiscussion
At least 17 skipjack tuna were observed and recorded swim-
ming close to the bow during fishing operations and vessel
displacements. Fish followed the boat movements adapt-
ing to changes in the vessel speed and direction. The skip-
jack tuna remained within 5–20m in front of the vessel at
the surface during hours when the vessel was travelling at
6–8 miles/hour (video footage, see Electronic Supplemen-
tary Material, A1). Fishes moved deeper when the vessel
stopped, disappearing from the camera focus and appar-
ently swimming slowly under the boat. Then, biologists
introduced a pole with a small camera recording the school
swimming at ~ 5–10m depth under the bow of the vessel
Online ISSN 2005-7172
Print ISSN 1738-5261
* Gonzalo Mucientes
gmucientes@iim.csic.es
1 Institute ofMarine Research, Spanish National Research
Council (IIM-CSIC), 36208Vigo, Spain
2 Research Centre inBiodiversity andGenetic
Resources(CIBIO/InBio), University ofPorto,
4485-661Vairão, Portugal
3 Ecoloxía Azul - Blue Ecology, 36208Vigo, Spain
4 Spanish Institute ofOceanography, Oceanographic Center
ofVigo, 36390Vigo, Spain
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G. Mucientes and N. Vilas-Arrondo
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(Fig.1a, b). The school of skipjack tunas was observed to
swim using the pectoral fins to adapt their speed to that of
the boat, as well as to move from left to right and back and
forward in front of the bow (video footage, https:// youtu. be/
6gk3f srqRos). The same behaviour was observed for several
consecutive days between 12 and 15 September—in all cases
with sea surface being calm. On one occasion, skipjack tunas
were observed to approach the catch of the longline (blue
shark, Prionace glauca) as it was being hauled (Fig.1c).
Even if it is relatively common for sport fishers to see
groups of tunas that swim near the boats in the open sea,
as far as we know, this is the first report of tunas swimming
in front of the bow of the vessel, and the first time it was
recorded. A similar behavioural association during brief
moments was previously reported in yellowfin tuna, Thunnus
albacares (Brill etal. 1999; Dagorn and Fréon 2001). One
possible explanation for our observation is that the skipjack
tuna considered the vessels a floating object. According to
the “meeting point” hypothesis (Dagorn and Fréon 1999),
there might be a social driver for the observed fish asso-
ciation with floating objects (drifting logs, anchored FADs,
vessels) as it may increase their chances of encountering co-
specifics and the opportunity for social interactions (Castro
etal. 2002; Robert etal. 2014). An alternative explanation
is that skipjack tuna used the vessel to move or migrate to
other places, as it has been observed in tunas associated
with dolphins. Specifically, yellowfin tuna use dolphins to
move from one floating object to the next (Scott etal. 2012).
The behaviour described in this work is apparently similar
to dolphins jumping in front of vessels, a common activ-
ity of small cetaceans (Luseau 2006). Given that tuna can
use dolphins to move or migrate, tuna might have imitated
dolphin behaviours.
Likewise, the observed phenomenon consisting in the
approach of the skipjack tuna to the catch of the vessel
(Fig.1c) could be compared to the behaviour of the pilot
fish, Naucrates ductor, an oceanic species with a semi-obli-
gate commensal relationship with sharks, rays, bill fish and
turtles (Vassilopopoulou etal. 2005) Finally, the reported
behaviour of skipjack tuna might be due to alterations in
anthropogenic sound. Indeed, boat noise can create a physi-
ological alteration in the bluefin tuna, Thunnus thynnus,
resulting in apparent avoidance behaviour that consists of
increased vertical movements in the water column that reach
the sea surface (Sará etal. 2007). Skipjack tuna could have
displayed similar avoidance diving behaviour at times during
our observations.
In conclusion, although we cannot arrive at definite con-
clusions about the ultimate drivers of the observed behaviour
of skipjack tuna swimming in front of the boat bow, our
observation expands the range of behaviours known about
this species.
Acknowledgements The crew of Ameal fishing vessel for their support
in the open ocean and to David Villegas-Ríos for providing insights to
the manuscript. GM was supported by a grant number ICETA 2017-49,
under the project I&D MarInfo–Integrated Platform for Marine Data
Acquisition and Analysis, NORTE-01-0145-FEDER-000031.
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