MARINE AND FISHERY SCIENCES 36 (1): 5-16 (2023)

https://doi.org/10.47193/mafis.3612023010102

ABSTRACT. Sea turtles are susceptible to a wide range of impacts. In Brazil, the loggerhead tur-

tle Caretta caretta (Linnaeus, 1758) is the main sea turtle species caught incidentally by longline

fishing fleets that target the blue shark Prionace glauca (Linnaeus, 1758) and swordfish Xiphias

gladius (Linnaeus, 1758). The latter is well known for its predation strategy, which consists of using

the rostrum to injure and catch prey. In this study, we recorded for the first time the impalement of

a juvenile loggerhead sea turtle by a swordfish during a fishing operation of a Brazilian longline ves-

sel in 2018. Two videos of this interaction were recorded by the shipmaster around 260 km from the

Brazilian coast. The sea turtle was incidentally caught with a hook and subsequently attacked by the

swordfish. The rostrum initially pierced the anterior left shoulder of the turtle and passed through

the body, exiting from the right posterior carapace. Given the position of the attack, considerable

internal damage was most certainly done to the turtle. Although the turtle was hauled aboard to

remove the hook and then returned to the sea alive, it probably died due to the extent of the injuries

caused by the rostrum having passed through the center of the body. Since both swordfish and turtle

are pelagic and these interactions are poorly recorded, such encounters may be relatively common.

Therefore, this type of information should be included in the data collection protocols of fishery

monitoring programs to better understand and scale the bill-stab phenomenon, not only for sea tur-

tles but also in relation to other groups of fauna.

Key words: Sea turtle, incidental capture, species interaction, fisheries, Southwestern Atlantic

Ocean.

Más allá de la pesca: empalamiento de una tortuga cabezona por el pez espada

RESUMEN. Las tortugas marinas son susceptibles a una amplia gama de impactos. En Brasil, la

tortuga cabezona Caretta caretta (Linnaeus, 1758) es la principal especie de tortuga marina captu-

rada incidentalmente por las flotas pesqueras de palangre que tienen como objetivo la tintorera

Prionace glauca (Linnaeus, 1758) y el pez espada Xiphias gladius (Linnaeus, 1758). Este último,

es muy conocido por su estrategia de depredación, que consiste en utilizar el rostro para herir y atra-

par presas. En este estudio, se registró por primera vez el empalamiento de un juvenil de tortuga

cabezona por un pez espada en 2018 durante una operación de pesca de un palangrero brasileño. El

capitán del barco grabó dos videos de esta interacción a unos 260 km de la costa brasileña. La tor-

tuga marina fue atrapada incidentalmente con un anzuelo y posteriormente atacada por el pez espa-

da. El rostro perforó inicialmente el hombro izquierdo anterior de la tortuga y atravesó el cuerpo,

5

*Correspondence:

fnfiedler@hotmail.com

Received: 21 June 2022

Accepted: 8 August 2022

ISSN 2683-7595 (print)

ISSN 2683-7951 (online)

https://ojs.inidep.edu.ar

Journal of the Instituto Nacional de

Investigación y Desarrollo Pesquero

(INIDEP)

This work is licensed under a Creative

Commons Attribution-

NonCommercial-ShareAlike 4.0

International License

Marine and

Fishery Sciences

MAFIS

ORIGINAL RESEARCH

Beyond fishing: loggerhead turtle impalement by swordfish

FERNANDO N. FIEDLER1, *, GILBERTO SALES2, RODRIGO BARRETO1, CAIAME J. NASCIMENTO3and

BRUNO B. GIFFONI4

1Centro Nacional de Pesquisa e Conservação da Biodiversidade Marinha do Sudeste e Sul (CEPSUL), Avenida Carlos Ely Castro 195

Centro, 88301-445 - Itajaí, Brazil. 2Centro Nacional de Pesquisa e Conservação de Tartarugas Marinhas e da Biodiversidade Marinha do

Leste (Centro TAMAR/ICMBio), 88061-160 - Florianópolis, Brazil. 3Independent researcher, 42830-034 - Camaçari, Brazil.

4Fundação Centro Brasileiro de Proteção e Pesquisa das Tartarugas Marinhas (Fundação Projeto Tamar), 11688-670 - Ubatuba, Brazil.

ORCID Fernando N. Fiedler https://orcid.org/0000-0001-5706-1937, Gilberto Sales https://orcid.org/0000-0002-6742-5551,

Rodrigo Barreto https://orcid.org/0000-0002-5737-9416, Caiame J. Nascimento https://orcid.org/0000-0002-6848-7375,

Bruno B. Giffoni https://orcid.org/0000-0002-7834-0609

INTRODUCTION

Sea turtles are subject to a wide range of

impacts and threats from human activity through-

out their life cycle (NRC 1990), such as exposure

to pollutants, collisions with vessels, and mainly

incidental capture by different fishing gear (Lazar

et al. 2011; Lewison et al. 2014; Schuyler et al.

2014; Ataman et al. 2021). In the latter case, the

loggerhead sea turtle Caretta caretta (Linnaeus,

1758) is one of the most widely incidentally cap-

tured species by longline fleets worldwide (Spoti-

la et al.2000; Yeung 2001; Lewison et al. 2004;

Lewison and Crowder 2007). The Southwestern

Atlantic Ocean is an important foraging and juve-

nile development area and is home to mixed

stocks of loggerhead turtles (Shamblin et al.

2014), which is the species that most interacts

with longline fleets in this region (Kotas et al.

2004; Sales et al. 2004, 2008; Domingo et al.

2006a, 2006b; López-Mendilaharsu et al. 2007;

Giffoni et al. 2008; Pons et al. 2010).

The swordfish Xiphias gladius (Linnaeus,

1758) is widely distributed worldwide, and par-

ticularly across the West Atlantic Ocean, from

Canada in the North to Argentina in the South

(Palko et al. 1981; Weidner and Arocha 1999). In

the Southwestern Atlantic, it is one of the main

target species of longline fisheries in the south-

east and south of Brazil and in Uruguay (Fiedler

et al. 2015). Moreover, it is considered an oppor-

tunistic species with a broad trophic spectrum

(Clarke et al. 1995; Figueiredo and Menezes

2000). The most striking morphological feature

of this species is an elongated and dorsolaterally

flat rostrum, which is mainly used to incapacitate

prey with a lateral movement (Wisner 1958;

McGowan 1988; Habegger et al. 2015).

Impalements caused by billfishes on different

taxonomic groups such as whales (Jonsgard

1962; Machida 1970; Oshumi 1973; Major

1979), sharks (Fierstine et al. 1997; Penadés-

Suay et al. 2017, 2019; Jambura et al. 2020;

Romeo et al. 2020), even humans (Carvajal et al.

2002; Gooi et al. 2007; Mendonça-Caridad et al.

2008; Haddad Jr and Figueiredo 2009; Geor-

giadou et al. 2010; Galarza et al. 2016), and

diverse inanimate objects, such as submarines

(Zarudzki and Haedrich 1974) and ships (Gudger

1940; Romeo et al. 2017) have been recorded

around the world. In contrast, records of turtles

impaled by billfishes are rare (Frazier et al.

1994), even today, when images can be quickly

captured using mobile phones. Furthermore,

impalements by billfish are usually identified

when the fishing gear is collected, when fishers

are fully focused on their catch and have no time

to record such events, which makes the opportu-

nity to obtain images even more difficult. Among

32 records identified since the 1940s, only 7

include information on the interaction between

billfish and sea turtles (Table 1). The turtle

species involved were olive ridley Lepidochelys

olivacea (3 records), leatherback Dermochelys

coriacea (2 records), and loggerhead and green

turtle Chelonia mydas (1 record each). The only

two interactions previously reported with Xiphias

gladius involved a Lepidochelys olivacea record-

6MARINE AND FISHERY SCIENCES 36 (1): 5-16 (2023)

saliendo por la parte posterior derecha del caparazón. Dada la posición del ataque, la tortuga sufrió un daño interno considerable.

Aunque la tortuga fue subida a bordo para quitarle el anzuelo y luego fue devuelta viva al mar, probablemente murió debido a la exten-

sión de las heridas causadas por el paso del rostro a través del centro del cuerpo. Dado que tanto el pez espada como la tortuga son

pelágicos y estas interacciones no se registran acabadamente, estos encuentros pueden ser relativamente comunes. Por lo tanto, este

tipo de información debe incluirse en los protocolos de recopilación de datos de los programas de monitoreo de pesquerías para com-

prender mejor y escalar este tipo de fenómenos, no solo para las tortugas marinas sino también en relación con otros grupos de fauna.

Palabras clave: Tortuga marina, captura incidental, interacción de especies, pesquerías, Océano Atlántico Sudoccidental.

7

FIEDLER ET AL.: LOGGERHEAD TURTLE IMPALEMENT BY SWORDFISH

Table 1. Literature review on the interaction of billfish and different groups of fauna (e.g. whales, sharks, and turtles), humans,

and inanimate objects (e.g. ships and submarines). *Brazilian EZZ: Brazilian Exclusive Economic Zone.

Year of Region/country Species/structure Billfish species Evidence

occurrence

Not reported Not reported Vessels Unknow Gudger 1940

1959 Antarctic sea Balaenoptera musculus Xiphias gladius Jonsgard 1959

1962 Antarctic sea Balaenoptera physalus Xiphias gladius Jonsgard 1962

1969 North Pacific Balaenoptera borealis Xiphias gladius Machida 1970

1972 Antarctic sea Balaenoptera Makaira mazara or Oshumi 1973

bonaerensis Istiompax indica

1967 Western Atlantic Ocean Submarine ‘Alvin’ Xiphias gladius Zarudzki and

Haedrich 1974

1951 Karuku Point, Oahu, Hawaii Unidentified whales Unknow Major 1979

1983 Off San José, Uruguay Dermochelys coriacea Makaira nigricans Achaval and

Prigioni 1988

1965 Off Cape San Lucas, Mexico Lepidochelys olivacea Xiphias gladius Frazier et al. 1994

1987 Ogasawara, Japan Chelonia mydas Istiophorus Frazier et al. 1994

platypterus

1989 150 km SW of Acapulco, Lepidochelys olivacea Istiophorus Frazier et al. 1994

Mexico platypterus

1989 480 km SSW of Acapulco, Lepidochelys olivacea Unknow Frazier et al. 1994

1992 Off Ventura, California, Caretta carreta Kajikia audax or Frazier et al. 1994

USA Makaira nigricans

1993 Off Algarve, Portugal Makaira nigricans Kajikia albida and Fierstine 1997

K. audax

1995 Off Enseñada, Mexico Isurus oxyrinchus Makaira nigricans Fierstine et al.

1997

Not reported Alicante, Spain Human (young male) Xiphias gladius Carvajal et al.

2002

Not reported Malaysia Human (adult male) Xiphias gladius Gooi et al. 2007

Not reported Spain Human (adult male) Xiphias gladius Mendonça-

Caridad et al.

2008

2008 Matinhos beach, Paraná, Human (adult male) Tetrapturus albidus Haddad Jr and

Brazil Figueiredo 2009

Not reported Satorini Island, Greece Human (adult woman) Xiphias gladius Georgiadou et al.

2010

2014 Grande Rivière beach, Dermochelys coriacea Unknow Martin 2014

2000 Spain Human (adult male) Xiphias gladius Galarza et al.

2016

ed in the Pacific Ocean, in the Cabo San Lucas

region (Mexico), and a Chelonia mydas recorded

in Japan (Frazier et al. 1994). Few records on the

interaction of swordfish with sea turtles were

found; however, a relatively larger number of

records were found of swordfish interacting with

other fauna groups and even inanimate objects

such as submarines, boats, and submersibles

(Ellis 2013).

In this regard, the present study provides the

first confirmed record of a loggerhead sea turtle

Caretta caretta impaled by a swordfish Xiphias

gladius.

METHODS

The impalement was recorded during the fish-

ing trip of a Brazilian longline vessel that specif-

ically fishes swordfish and shark, in August 2018.

The master of the vessel recorded two videos

each of 1 min 39 s using his smartphone. In the

first video, the turtle and swordfish reported on

herein were still in the water, before were brought

aboard, while, in the second video, the swordfish

and turtle were being boarded onto the vessel.

These videos were voluntarily given by the mas-

ter to the team of the Tamar Project Foundation (a

Brazilian non-governmental organization that has

been working for the conservation of sea turtles

for more than 40 years), in the port of Itajaí, Santa

Catarina state, southern Brazil.

RESULTS

On August 16th 2018, while reeling the third

longline set at position 26° 25'78"S and 46° 00'

69"W, about 260 km from the port of origin in

Itajaí (SC), Brazil, between 500 m and 1000 m

deep (Figure 1), a juvenile loggerhead turtle was

found hooked, and at some point the hooked tur-

tle had been impaled by a swordfish with its

sword still piercing the body of the turtle (Figure

8MARINE AND FISHERY SCIENCES 36 (1): 5-16 (2023)

Table 1. Continued.

Year of Region/country Species/structure Billfish species Evidence

occurrence

Not reported Senegal Human (4 adult male Xiphias gladius Ndiaye et al. 2017

and 1 young male)

2016 Valencia, Spain Prionace glauca Xiphias gladius Penadés-Suay et al. 2017

1999-2014 Sicilian waters Harpoon fishing vessels Xiphias gladius Romeo et al. 2017

Not reported Malaysia Human (adult male) Xiphias gladius Sriram et al. 2017

2017 Garrucha, Spain Prionace glauca Xiphias gladius Penadés-Suay et al. 2019

2017 Ostia, Italy Prionace glauca Xiphias gladius Penadés-Suay et al. 2019

2018 Vera, Spain Prionace glauca Xiphias gladius Penadés-Suay et al. 2019

2018 Manacor, Spain Prionace glauca Xiphias gladius Penadés-Suay et al. 2019

2020 Brega, Libyan Alopias superciliosus Xiphias gladius Jambura et al. 2020

2018 Sicilian waters Prionace glauca Xiphias gladius Romeo et al. 2020

2018 Southwestern Atlantic Caretta caretta Xiphias gladius This study

Ocean (Brazilian EEZ)

2 A). The rostrum of the swordfish pierced the

anterior region of the turtle between the neck and

the shoulder of the left flipper, passing through

the carapace and exiting from the right side of the

fourth central scute, approximately between the

fourth and fifth right lateral scute (Figure 2 B). At

the time of encountering between the two ani-

mals, the turtle was alive, and the swordfish was

dead. Before boarding the two animals, the body

of the swordfish was removed by the fishers to

facilitate hauling onto the deck, and only the head

with the rostrum remained attached to the turtle

(Figure 2 B and 2 C). After recording, the head

and rostrum of the swordfish were removed from

the turtle (Figure 2 D) and the turtle was returned

to the sea.

DISCUSSION

The way the swordfish was attached to the tur-

tle suggests that the attack was made in the same

horizontal plane as the turtle or at a slightly lower

9

FIEDLER ET AL.: LOGGERHEAD TURTLE IMPALEMENT BY SWORDFISH

Figure 1. Location where the loggerhead turtle Caretta caretta was captured incidentally by longline vessel and impaled by a

swordfish Xiphias gladius.

angle since the rostrum was attached longitudi-

nally to the turtle’s body. Considering the posi-

tion/orientation in which the rostrum of the

swordfish perforated the turtle, it is very likely

that at least one of the turtle’s lungs was struck

since they occupy a large area just below the cara-

pace. Furthermore, since the perforation occurred

longitudinally, from anterior to posterior of the

turtle’s body, and relatively diagonally (from ven-

tral to dorsal), other organs such as the gastro-

intestinal tract, heart, liver, and other structures

such as veins and arteries were also affected. If

indeed other organs and structures were perforat-

ed, the possibility of this turtle having survived

was very low. Although the animal was returned

to the sea alive, it probably died due to the extent

of the internal injuries caused by the impalement.

In June 2014, a leatherback turtle was observed

nesting on Grande Riviere beach in Trinidad,

Caribbean, with the rostrum of a billfish stuck into

its carapace (Martin 2014). This rostrum was

approximately 60 cm long and entered the turtle

transversely through the carapace and exited

through the plastron. According to the published

note, the rostrum perforating the turtle’s carapace

was encrusted by barnacles, indicating that it had

been embedded in the turtle for some time. There-

fore, the interaction of the turtle with the billfish

had not been recent and, despite any damage

caused by the impalement, the turtle had survived

(Martin 2014). The fact that the rostrum traversed

the turtle’s body from one side to the other sug-

gests that at least one of the turtle’s lungs had been

punctured. Regardless, the female leatherback tur-

tle was able to leave the sea and climb up the

beach to lay eggs, demonstrating the incredible

resistance of these animals to the injuries suffered.

The first known record of a sea turtle impaled

by a billfish was made in 1988, when Uruguayan

researchers reported the case of a leatherback tur-

tle impaled by the rostrum of a blue marlin

Makaira nigricans (Achaval and Prigioni 1988).

Four cases of turtle impalement, including the

previous one, were subsequently described (Fra-

zier et al. 1994). These include impalements by

sailfish Istiophorus platypterus, blue marlin, and

swordfish, and involve the leatherback turtle,

olive ridley sea turtle, and the green sea turtle. In

addition to these confirmed instances, the case of

a loggerhead turtle with a fragment of the rostrum

of the striped marlin Kajikia audax or M. nigri-

cans in its carapace, parallel to the ribs, caught in

a gill net in the USA was recorded. However,

10 MARINE AND FISHERY SCIENCES 36 (1): 5-16 (2023)

Figure 2. A) Loggerhead sea turtle Caretta caretta (alive)

with the swordfish Xiphias gladius (dead) that has

impaled the turtle. B) At this point, the decapitated

head of the swordfish with its rostrum passing

through the turtle: red circles show sites of entry and

exit of rostrum. C) Ventral view of the turtle, with

the steel wire (red circle) or ‘strop’, part of the long-

line gear in the mouth of the turtle, indicating that the

fishing gear first hooked the turtle. D) Fishers

removing the rostrum of the swordfish from the body

of the turtle. Images taken from the two videos

recorded by the master of the vessel.

there was no photographic record for validation

(Frazier et al. 1994).

The South Atlantic Ocean is an important area

for the reproduction, feeding, and growth of

swordfish, from larval to adult stage (Gorbunova

1969; Hazin and Erzini 2008). Swordfish migrate

horizontally and move vertically daily from

depths over 600 m, where they remain during the

day, to the surface at night (Carey and Robison

1981). Therefore, it is during the night that

swordfish and loggerhead turtles may occupy the

same water strata. A study carried out on logger-

head turtles caught incidentally by pelagic long-

lines in the Southwestern Atlantic and subse-

quently released with satellite transmitters,

revealed that the deepest dives carried out by

these animals were between 200 m to 300 m

deep. However, only 1% of all monitored dives

exceeded 100 m in depth and the loggerhead tur-

tles usually remained between depths of 10 m and

100 m (Barceló et al. 2013). Therefore, these

interactions between swordfish and sea turtles

should mainly occur at night, which is also the

time the longline vessels targeting swordfish set

their gear in the water.

At feeding times, swordfish can reach speeds of

more than 100 km h-1. The elongated, fusiform

body and large, light, thin, and profoundly forked

tail of the swordfish cause relatively little resist-

ance and require less effort than would be required

by less hydrodynamically designed fish, thus

allowing the swordfish to achieve very high

speeds (Ellis 2013). Moreover, top predators, such

as the swordfish, have a highly specialized ther-

moregulatory system located in an extraocular

muscle that maintains the eyes and brain up to

15 °C above water temperature (Carey 1982), sig-

nificantly improving the temporal resolution (10

times better than that of fish with eyes at the same

temperature as that of surrounding water), increas-

ing movement detection and providing a huge

advantage over the prey (Frietsches et al. 2005).

The rostrum has sensitive lateral lines that

detect pressure differences in the water and

enable the best angle for approach and attack

(Scott and Tibbo 1968; Nakamura 1983; Lee et al.

2009; Sagong et al. 2013; Habegger 2014). Pred-

ators with narrow body profiles and great swim-

ming speed, such as swordfish, can approach

their prey without triggering an escape response,

which increases their chances of successful

attacks (Webb 1986). In this regard, the rostrum

of billfish plays a critical role in feeding since

these species have one of the lowest absolute bite

forces among all bony and cartilaginous fish

(Habegger et al. 2017).

Studies on the swordfish diet carried out in

southeastern and southern Brazil recorded a high-

er frequency of the occurrence of cephalopods,

followed by bony fish (Mazzoleni and Schwingel

2002; Vaske Júnior and Lessa 2005; Gorni et al.

2012, 2013). Although turtles are not part of the

regular diet of swordfish or any other billfish,

impalements may be caused by an accidental col-

lision since this type of attack is not beneficial for

the swordfish as corroborated by Frazier et al.

(1994). These impalements may occur when the

swordfish tries to capture prey close to the turtle,

which often remains immobile on the surface and

tends to float, thus serving as an aggregator of

small fish that, in turn, can attract larger preda-

tors, such as the swordfish (Brock 1985; Frazier

et al.1994; Hirama and Witherington 2012). It

could also be that billfish in urgent need of feed-

ing may make risky attacks near to a dangerous

object, which would otherwise be avoided by a

billfish not under feeding stress.

In the present case, the turtle was attached to a

longline hook, resulting in a limited swimming

radius due to the length of the branchline

(between 15 m and 20 m), which forces the turtle

to swim in a circle or up and down to breathe or

submerge. This unnatural swimming pattern may

have attracted the attention of the swordfish. A

similar event was recorded in Mexico, when an

olive ridley sea turtle was captured by a longline

boat and was also impaled by a swordfish (Fra-

zier et al.1994). Some abundant data about this

11

FIEDLER ET AL.: LOGGERHEAD TURTLE IMPALEMENT BY SWORDFISH

species, including reports of interaction with dif-

ferent groups of fauna or structures can be found

in Ellis (2013).

Accidents with humans have also been report-

ed and, although rare, often result in serious

injuries to those attacked (Carvajal et al.2002;

Mendonça-Caridad et al.2008; Haddad Jr and

Figueiredo 2009; Georgiadou et al.2010; Galarza

et al. 2016; Sriram et al.2017). Many of these

cases of human attacks involve fishers, who are

evidently more susceptible to interactions with

billfish. Such incidents generally occur when the

billfish are provoked or when they feel threatened

and use the rostrum to defend themselves (Romeo

et al.2017).

The amount of evidence to date on impalement

of sea turtles and other taxa (including humans)

by billfish raise the question about the frequency

of these interactions. Therefore, this type of infor-

mation should be included in the data collection

protocols of fishery monitoring programs to bet-

ter understand and scale the impalement phenom-

enon, not only for sea turtles but also in relation

to other groups of fauna.

ACKNOWLEDGEMENTS

The authors are grateful to captain Wesley,

who generously allowed us to use the video of the

impaled turtle and who advised us about the event

that we report on herein, without which this work

would not be possible. We also thank the review-

ers for critical reading and suggestions for the

manuscript.

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