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Revista de Biología Tropical, ISSN: 2215-2075 Vol. 69(Suppl. 2): S246-S255, October 2021 (Published Oct. 30, 2021)

Residency of bull sharks, Carcharhinus leucas

(Carcharhiniformes: Carcharhinidae), at San Pedrillo Islet

in Islas Murciélago, North Pacific of Costa Rica

Andrés López-Garro1; https://orcid.org/0000-0001-7834-5306

Ilena Zanella1; https://orcid.org/0000-0002-3820-7643

1. Asociación Conservacionista Misión Tiburón, Playas del Coco, Guanacaste, Costa Rica; alopez@misiontiburon.org,

izanella@misiontiburon.org

Received 21-XII-2020. Corrected 08-II-2021. Accepted 05-V-2021.

ABSTRACT

Introduction: The bull shark, Carcharhinus leucas, is particularly vulnerable to anthropogenic actions because

of its permanence in coastal ecosystems; populations depletion is registered in different places around the world.

Aggregations of bull sharks have been reported in the North Pacific of Costa Rica, at Islas Murciélago, within

the Guanacaste Conservation Area.

Objective: To study the residency of bull sharks at San Pedrillo islet, Islas Murciélago.

Methods: During the study period (June 2013 to February 2015) we used passive telemetry to tag 10 bull sharks.

Results: All the sharks tagged were females, they were detected on 59 798 occasions by the acoustic receiver

deployed in San Pedrillo. Acoustic signals from tagged sharks were received for a total period of 1 to 229 days

(mean = 73.9 ± 71.3 days), with the last detections occurring on 9 January 2015. The Residency Index for each

tagged shark across the entire monitoring period ranged from 0.41 to 1.00. The bull shark activity showed a

significant pattern throughout the day at the receiver that specifically corresponded with the daily light cycle.

Conclusions: This study concludes that San Pedrillo is an aggregation site (cleaning station) for bull sharks (C.

leucas), possibly related to reproduction and not feeding behaviors.

Key words: Carcharhinus leucas; Guanacaste; tagging; acoustic telemetry; aggregation site.

López-Garro, A., & Zanella, I. (2021). Residency of bull sharks,

Carcharhinus leucas (Carcharhiniformes: Carcharhinidae),

at San Pedrillo Islet in Islas Murciélago, North Pacific of

Costa Rica. Revista de Biología Tropical, 69(Suppl. 2),

S246-S255. https://doi.org/10.15517/rbt.v69iS2.48321

https://doi.org/10.15517/rbt.v69iS2.48321

The Archipelago of Islas Murciélago is

part of the Marine Sector of the Guanacaste

Conservation Area, in the north Pacific of

Costa Rica. One of the top predators of this

area is the bull shark, Carcharhinus leucas

(Valenciennes 1839), which is a cosmopolitan

tropical and subtropical species commonly

found in coastal ecosystems such as estuar-

ies, lagoons, and river mouths thanks to their

capacity to enter freshwater systems (Com-

pagno, 1984). Like other elasmobranchs, the

bull shark uses estuaries and river mouths as

nurseries. The fact that these systems are also

of high productivity could be one of the reasons

why adult female bull sharks prefer these sites

to give birth (Curtis, Parkyn, & Burgess, 2013).

Several authors have reported bull sharks using

coastal ecosystems for protection and food

during their early life stages (Simpfendorfer,

Greitas, Wiley, & Heupel, 2005; Werry &

Clua, 2013). Nursery grounds for bull sharks

have been documented in the Gulf of Mexico

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and the east coast of Florida (Curtis, Adams, &

Burgess, 2011). Bull shark juveniles can access

rivers to feed, preying on species that migrate

between rivers and oceans during tidal changes.

Numerous studies have also reported the pref-

erence or habitat fidelity of adult bull sharks to

shallow waters of coastal habitats, particularly

to those with a high input of freshwater, such as

river mouths and estuaries (Bangley, Paramore,

Shifman, & Rulifson, 2018; Brunnschweiler,

Queiroz, & Sims, 2010; Carlson, Ribera, Con-

rath, Heupel, & Burgess, 2010; Graham et al.,

2016; Heupel et al., 2015). The permanence of

bull sharks in coastal ecosystems makes them

vulnerable to anthropogenic actions like habitat

degradation, pollution, and fishing exploitation

(Curtis et al., 2013; Thorson, 1971; Werry &

Clua, 2013).

Bull shark population depletion is reported

in different places around the world, such as

the Gulf of Mexico and the southwest Atlantic

of Brazil (Almeida, McGrath, & Ruffino, 2001;

Powers et al., 2013). In Central America, spe-

cifically in Lake Nicaragua, exploitation of bull

sharks started in the 1960s, when they were

consumed domestically and exported overseas

(Thorson, 1982). In the 1970s an Asiatic shark

fin processing plant started to operate near

Granada. In Lake Nicaragua, the bull shark

fishery industry collapsed in the 1980s, yet the

population has still not recovered from overex-

ploitation (McDavitt, 2002).

Bull sharks currently have a higher eco-

nomic value as a tourist resource, related to

recreational diving, than as a commercial spe-

cies. For example, at Cabo Pulmo National

Park (CPNP), Mexico, the bull shark is one of

the main attractions for tourists. According to

Pasos-Acuña (2018), bull shark recreational

diving at CPNP represents more than $7.5 mil-

lion each year. Worldwide, it is estimated that

half a million people are interested in shark

diving, generating more than US$314 million

per year and more than 10 000 jobs. Further-

more, it is expected that in the next 20 years

shark tourism is going to double at a global

scale, potentially generating more than US$750

million annually (Cisneros, Barnes, Navarro, &

Rashidsumaila, 2013).

In Costa Rica, bull shark juveniles and

adults are occasionally caught by artisanal

fishermen (bottom line and gill nets) who fish

close to river mouths and estuaries (López,

Arauz, Zanella, & Le Foulge, 2009; López &

Zanella, 2015). The exploitation of bull sharks

in Costa Rica has been developed without

any specific management regulation. The San

Pedrillo islet, located at Islas Murciélago archi-

pelago, has been identified empirically as an

aggregation site for bull sharks, the only one

reported for the species in Costa Rica. During

the rainy season (May-November), local com-

munities such as Playas del Coco, Tamarindo,

and Cuajiniquil, directly benefit from SCUBA

diving with bull sharks in a completely natural

environment (Davis & Klapfer, 2018). In this

study, we used acoustic telemetry to monitor

the residence of adult bull sharks at the San

Pedrillo islet. This study will add new informa-

tion for the design of conservation strategies to

improve the protection of the bull shark popu-

lation at the Conservation Area of Guanacaste

and surrounding areas.

MATERIALS AND METHODS

Study area: The archipelago of Islas Mur-

ciélago is located in the north Pacific of Costa

Rica, 5 km off mainland Costa Rica, and is

comprised of five islands and ten islets, one

of them being San Pedrillo (10º51’12.4”N &

85º57’32.5” W) (Denyer, Cortés, & Cárdenes,

2005). As part of the Área de Conservación

Guanacaste (ACG, Guanacaste Conservation

Area), the Islas Murciélago belong to a UNES-

CO World Heritage Site; part of the Sistema

Nacional de Áras de Conservación (SINAC,

National System of Conservation Areas of

Costa Rica) from the Ministry of Environment

of Costa Rica (SINAC, 2013). The archipelago

is a no-take Marine Protected Area with an

extension of 43,000 ha where only tourism

activities are allowed. The marine biodiversity

of Islas Murciélago is influenced by a seasonal

upwelling (from December to March) that rises

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cold deep water masses that generate an intense

effect on the distribution of nutrients and

plankton (Jiménez, 2016; Rodríguez, Alfaro, &

Cortés, 2021).

Acoustic array and shark tagging: Tag-

ging was performed between June 2013 and

September 2014 at San Pedrillo islet between

18 and 30 m depth, where the aggregation of

adult bull sharks is known to occur (Davis

& Klapfer, 2018). An acoustic receiver was

deployed at the same site using SCUBA gear.

The tags or acoustic transmitters were V16-4H

with external cases (Vemco Ltd., Halifax, Nova

Scotia, Canada), which were tethered to stain-

less steel darts. Scuba divers inserted the darts

into the muscle of the bull sharks at the base of

the first dorsal fin. The researchers reported the

sex of each shark tagged (presence or absence

of claspers) and estimated the size (total length)

of the shark. The sharks were tagged during

the rainy season when the upwelling is not

occurring and ocean conditions favor diving

activities and underwater tagging. Transmitters

were set to be silent (delay) for a random-

ized period of 40 to 140 s between each pulse

train and had a battery life of approximately 4

years. Each transmitter tag conveyed a specific

code for an individual shark, and periodically

emitted a pulse train of closely spaced 69 kHz

pings detected by the receiver VR2W (Vemco

Ltd., Halifax, Nova Scotia, Canada), which

was deployed before tagging on the 12th

of June 2013. The receiver was placed at a

depth of 30-35 m in a sandy bottom close to

the aggregation site, next to the San Pedrillo

islet. The receiver was anchored on a 65 kg

cement block attached to a stainless-steel cable

and suspended in the water column (approxi-

mately 3-5m from the bottom) with a buoy. The

receiver stored the information emitted from

the transmitters (date, time of the detection,

and transmitter number for each individual

pulse train) along a 250-300 m radius, veri-

fied via range tests. The detection of the tags

decreased abruptly after 250 m, and tags were

not detected at distances greater than 300 m.

Receiver data was downloaded approximately

every 5 months, for 1.5 years (June 2013 to

February 2015).

Data analysis: The data recorded by the

acoustic receiver in San Pedrillo was down-

loaded using the software VUE version 2.0.6.

Shark detections during the study period were

plotted using the ‘ggplot’ package in R version

3.6.3 (R Development Core Team R, 2014).

To determine whether an individual was pres-

ent on any day close to the receiver, we set a

minimum of three detections as a metric. The

detections were compared: a) between indi-

viduals using the no-parametric test Kruskall

Wallis; b) between months of the rainy season

(May-November) and months of the dry season

(December-April) using the no-parametric test

Wilcoxon (Infostat, 2008). The Residency

Index (RI) was further calculated for each bull

shark tagged to better examine occurrence

patterns across the array. RI was defined as

the number of days a bull shark was detected

within the receiver array, divided by the num-

ber of days monitored (i.e. number of days

from the tagging date to the last date detec-

tions were received for all transmitters) (Espi-

noza, Farrugia, & Lowe, 2011; Papastamatiou,

Friedlander, Caselle, & Lowe, 2010; Zanella,

López, & Cure, 2019); RI values range from

0 to 1, with a value of 1 indicating the highest

possible residency at the receiver array. The

average number of detections per individual

tagged shark throughout a daily cycle was plot-

ted using ‘ggplot’ and ‘plyr’ packages in R

version 3.6.3 (R Development Core Team R,

2014). The environmental variables of Sea Sur-

face Temperature, SST (°C) and Chlorophyll-α

concentrations (mg/m3) were downloaded from

NASA’s OceanColor platform (www.ocean-

color.nasa.org), with a resolution of 4 km,

whose source is the National Oceanic and

Atmospheric Administration (NOAA). Those

files were downloaded in HDF format. Data

was downloaded monthly from June 2013 to

February 2015. Processed data was exported

as an ASCII file using the QGIS and DIVAGIS

software, these layers were used to extract the

information from at least 6 points around the

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Islas Murcielago, to an optimal representation

of the area. Residual normality test (Shapiro)

and homoscedasticity of variances test (Lev-

ene) were conducted. Since data was normal

and homoscedastic, comparisons were made

between seasons of the year (dry and rainy)

with paired t-student tests, performed with 95

% confidence (Infostat, 2008). We compared

the detections of tagged sharks at the receiver

between day (06:00-17:00) and night hours

(18:00-5:00), using the Wilcoxon nonpara-

metric test (Infostat, 2008), and we described

the average number of detections per indi-

vidual tagged shark at the receiver throughout

a daily cycle.

Research Permit: All the activities related

to this study were done in compliance with

the resolution of scientific permits Nº ACG-

PI-004-2013, Nº ACG-PI-017-2014 and Nº

ACG-PI-030-2015. Such permits were autho-

rized by the Área de Conservación Guana-

caste (ACG, Guanacaste Conservation Area)

of the SINAC, Ministry of Environment of

Costa Rica.

RESULTS

Between June 2013 and September 2014,

we tagged ten adult female bull sharks (C. leu-

cas) at San Pedrillo, Islas Murciélago. Based on

the approximate size of the individuals (> 2 m

total length) we classified them as “adults” fol-

lowing the maturity size estimation determined

in the Gulf of México and Northern Brazil

(Cruz-Martínez, Chiappa-Carrara, & Arenas-

Fuentes, 2004; Niella, Afonso, & Hazin, 2017).

During the study period (June 2013 to February

2015) a total of 59,798 detections were record-

ed by the acoustic receiver. Acoustic signals

from tagged sharks were received for a total

period of 1 to 229 days (mean = 73.9 ± 71.3

days), with the last detections occurring on 9

January 2015 (Table 1). The number of detec-

tions was not significantly different between

individuals (H = 9.00, P > 0.05).

The detections of tagged bull sharks

recorded in the receiver were higher during the

rainy season (May-November) compared with

the detections recorded during the dry season

(December-April) (W = 1593.00, P < 0.05), as

more than 80% of the detections were recorded

between May and November. The months of

July and August together provided almost 50%

of all detections, therefore they are considered

the most outstanding months for bull sharks

in this area. Even though some sharks were

detected during the dry season (December-

February), less than 20% of detections were

registered for the first months of the year (Fig.

1, Table 2).

TABLE 1

Residency of Carcharhinus leucas monitored in San Pedrillo, Islas Murciélago, Costa Rica. Sex: F=females;

Residency Index (RI): the number of days a shark was detected within the receiver array divided by

the number of days monitored. All sharks were detected at the receiver

Tag # Tag ID Tagging

date

Last d

etection Sex Size

(m)

No of

detections

Days

monitored

Days

detected RI

1 30322 20-06-13 04-02-14 F >2 16127 229 193 0,84

2 58967 12-06-14 26-09-14 F >2 10520 75 68 0,91

3 25468 27-09 -14 09-01-15 F >2 16804 135 135 1,00

4 25466 27-09-14 09-01-15 F >2 5715 135 59 0,44

5 58968 12-06-14 21-07-14 F >2 5170 39 33 0,85

6 25465 27-09-14 13-10-14 F >2 1766 48 43 0,90

7 25467 15-06-14 10-07-14 F >2 1744 25 14 0,56

8 30321 20-06-13 12-07-13 F >2 1238 22 9 0,41

9 30320 15-06-14 15-07-14 F >2 707 30 28 0,93

10 30319 12-06-14 12-06-14 F >2 7 1 1 1,00

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Regarding environmental variables (SST

and Chlorophyll-α concentrations), the tem-

perature was significantly higher during the

months of the rainy season compared with the

months of the dry season (t = 8.82, P < 0.0001);

whereas the Chlorophyll-α concentrations were

significantly lower during the months of the

rainy season compared with the months of the

dry season (t = -7.79, P < 0.0001; Table 2).

The Residency Index for each tagged shark

across the entire monitoring period ranged from

0.41 to 1.00 (Table 1) and there wasn´t a clear

tendency to monthly variation in residency

metrics (Fig. 2). During the time of this study,

bull shark activity showed a significant pattern

throughout the day at the receiver that specifi-

cally corresponded with the daily light cycle.

Detections were significantly highest from the

early morning to late afternoon (6:00 h to 18:00

h) (W = 6862.50, P < 0.0001) (Fig. 3).

DISCUSSION

This study confirmed that adult bull sharks

use San Pedrillo as an aggregation site. This

islet, located in the Marine Protected Area of

the ACG, is a site where bull sharks remain

for long periods, especially during the rainy

season (May-November), mostly with short

absences of 1 to 3 days. Even though some

bull sharks visited San Pedrillo during the dry

TABLE 2

Average monthly detections of Carcharhinus leucas, Sea Surface Temperature (SST, °C) and Chlorophyll-α

concentrations (mg/m3) monitored in San Pedrillo, Islas Murciélago, Costa Rica

Month Average of Detections ± SD Average of SST (ºC) ± SD Average of Chlorophyll-α (mg/m3) ± SD

June 517.66 ± 424.15 27.89 ± 0.01 0.22 ± 0.08

July 2 673 ± 2 126.69 28.83 ± 0.01 0.41 ± 0.00

August 2 486.40 ± 2 268.54 29.24 ± 0.03 0.42 ± 0.01

September 1 550 ± 942.33 29.44 ± 0.02 0.31 ± 0.05

October 1 089.50 ± 1 054.40 28.92 ± 0.02 0.32 ± 0.00

November 1 817.00 ± 1 553.30 28.66 ± 0.02 0.74 ± 0.00

December 2 899.00 ± 1 951.07 27.87 ± 0.01 1.36 ± 0.07

January 1 170.33 ± 922.91 27.31 ± 0.01 2.36 ± 0.03

Febraury 5 ± 0 26.97 ± 0.18 4.75 ± 0.03

March 0.00 28.52 ± 0,06 0.89 ± 0,00

April 0.00 28.35 ± 0,01 0.65 ± 0,00

May 0.00 30.02 ± 0,37 0.21 ± 0,06

Fig. 1. Number of detections per month of bull sharks

(Carcharhinus leucas) tagged at San Pedrillo, Islas

Murciélago, ACG, Costa Rica during the study period

(June 2013-Febraury 2015).

Fig. 2. Residency Index of bull sharks (Carcharhinus

leucas) tagged at San Pedrillo, Islas Murciélago, ACG,

Costa Rica during the study period (June 2013-Febraury

2015).

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months, less than 20% of total detections cor-

respond to December to February. This study

also confirmed that during the dry season the

marine area around Islas Murcielago experi-

ment a significant decrease of the temperature

and a significant increment of Chlorophyll con-

centration, as a result of the seasonal upwelling

reported for the North Pacific of Costa Rica,

produced by strong winds from the Caribbean

(Jiménez, 2016; Rodríguez et al., 2021). These

changes in environmental variables correspond

to a significant decrease in the detections of bull

sharks in the study area. Such behavior patterns

of temporary residence by bull sharks have

also been reported in South Africa, Mexico and

Fiji, where authors make a close connection

between residence and change in water tem-

perature and food availability (Brunnschweiler

& Barnett, 2013; Brunnschweiler, Queiroz,

& Sims, 2010; Daly et al., 2014). Daly et al.

(2014) described a site known as “Pinnacle

reef” in Mozambique, as an important aggrega-

tion site for adult bull sharks who reside there

for long periods, mainly during the summer

austral months (November-May).

Several studies have reported local migra-

tions of bull sharks, which is correlated to

seasonal changes (Daly et al., 2014; Niella,

Afonso, & Hazin, 2017). Satellite tags on

bull sharks have revealed important coastal

migrations, thus contradicting many theories

that this species is sedentary in coastal waters,

such is the case in the Gulf of Mexico, where

tagged bull sharks covered between 2 to 1 500

km in only 85 days, using primarily temper-

ate shallow waters (> 20 m depth) (Carlson

et al., 2010). Another example is a male bull

shark who covered more than 3 000 km in

75 days, mostly waters > 20 m depth along

the Brazilian coast (Niella, Afonso, & Hazin,

2017). Similarly, off the coast of Australia,

Heupel et al. (2015) described migration pat-

terns of bull sharks with a range greater than

1 700 km. Some authors suggest that the Great

Barrier Reef plays an important ecological

role for adult bull sharks off the east coast of

Australia, where sharks move between differ-

ent coastal habitats primarily in the search for

warmer waters.

At San Pedrillo, the lowest number of

detections were reported during the night, sug-

gesting that the bull sharks take part in local

migrations outside of San Pedrillo, possibly for

feeding purposes. The data also revealed that

most of the tagged sharks in San Pedrillo made

daily migrations during the entire study period.

Such results can be compared to other studies

like the one off the east coast of Africa (Daly

et al., 2014), which showed bull sharks’ loyalty

to “Pinnacle reef” was higher during daytime

than at nighttime. Brunnschweiler and Barnett

(2013), conclude that bull sharks move during

the daytime at a local scale mainly for feeding

purposes, utilizing different coastal habitats

based on the different times of the day.

All the sharks tagged in this study were

females, no males were observed during the

dives for tagging. Local divers reported the

presence of mostly females in the study area

and they observed some of them with scars

from bites along their body’s sides (Fig. 4), and

in few occasions, divers have reported a chas-

ing behavior of male individuals to females.

At the same time, cleaner fishes around rocky

reefs are constantly observed in San Pedrillo

dive site (pers. comm. Vallejos E., Rojas E.,

Berrocal D., 2019).

Fig. 3. Average number of detections per individual tagged

shark at the receiver throughout a daily cycle, San Pedrillo,

Islas Murciélago, Costa Rica, during the study period (June

2013-February 2015).

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In Costa Rica, aggregations of sharks’

adult females were reported for the scalloped

hammerhead shark (Sphyrna lewini) in the

oceanic Isla del Coco (Cocos Island), where the

sharks aggregate in specific cleaning stations

(Nalesso et al. 2019). Nalesso et al. (2019) con-

cluded that the scalloped hammerhead sharks

in Isla del Coco were more resident compared

with other oceanic islands (RI = 0.52 ± 0.31),

demonstrating that the sharks are strongly

associated with that island. The residence of

the bull shark (RI = 0.77 ± 0.21) in San Pedrillo

suggests that the site is an important aggrega-

tion site for the species. The values of RI (0.44-

1.00) reported in this study are higher than the

reported for “Pinnacle reef” in Mozambique,

where the sharks showed an RI influenced by

different factors such as reproductive activity,

environmental fluctuations, prey availability,

among others (Daly et al., 2014).

We concluded that San Pedrillo is a tem-

porary residence for the bull shark, and it is an

important aggregation site related to reproduc-

tion, not feeding behaviors. It is also impor-

tant to highlight that diving activities at San

Pedrillo are carried out during the day (between

8:00 and 12:00) in the rainy season when

environmental conditions allow the arrival of

tourist boats to the site. The higher detection

of bull sharks during daytime hours and their

interaction with recreational divers makes it

necessary to promote good practices for recre-

ational diving in San Pedrillo. At the moment,

no shark attacks have occurred at the study site,

but it has already been shown that the greatest

impact between divers and bull shark occurs

when divers perform irresponsible practices

(Pasos-Acuña, 2018).

San Pedrillo islet is a critical site for the

bull shark, however, more studies are needed

to identify feeding and nursery grounds in the

Guanacaste Conservation Area and surround-

ing areas. The identification and protection

of critical habitats for this iconic species will

bring environmental and social-economic ben-

efits to local communities of Guanacaste.

Management recommendations

1. Long residence periods of bull sharks in

the islet of San Pedrillo, as well as their

local migrations, make them a vulnerable

Fig. 4. Bull shark (Carcharhinus leucas) female with bite scars observed at San Pedrillo, Islas Murciélago, Costa Rica.

Photography credit: Daniel Berrocal, Okeanos Aggressor.

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species to fishing pressures and habitat

loss. Therefore, we recommend increasing

conservation and protection efforts at Islas

Murciélago, especially at San Pedrillo, a

site considered essential and critical for

the species.

2. It is important to expand the knowledge

and understanding of bull shark habitat use

in San Pedrillo. Efforts should also focus

on the identification of nursery and fee-

ding grounds for the creation of effective

conservation measures that guarantee the

protection of the species during all its life

cycle. The boundary of the MPA is located

less than 2 km from San Pedrillo, therefo-

re, we recommend the creation of a buffer

zone to decrease the impact of fisheries on

the species. The bull shark is a top predator

and an umbrella species, the conservation

of its critical habitats will improve the pro-

tection of other marine species.

3. Its urgent to involve local communities

in the protection of bull sharks through

the implementation of training and edu-

cational environmental programs. The

protection of the species will bring envi-

ronmental and socio-economic benefits

to the local communities that base their

economy on tourism.

4. Demonstrating the socio-economic bene-

fits of bull shark conservation will be

essential to improve the involvement of

local stakeholders and governmental ins-

titutions, thus is necessary to estimate the

economic value that bull sharks represent

to the local communities, especially for

Playas de Coco and Cuajiniquil.

Ethical statement: authors declare that

they all agree with this publication and made

significant contributions; that there is no con-

flict of interest of any kind; and that we

followed all pertinent ethical and legal proce-

dures and requirements. All financial sources

are fully and clearly stated in the acknowled-

gements section. A signed document has been

filed in the journal archives.

ACKNOWLEDGMENTS

The study was successfully carried out

thanks to the collaboration and support of

various organizations, institutions, divers, and

ocean lovers. Thanks to the team of Seamaster

Costa Rica, (especially to Cristiano Paoli for

helping during the tagging), Área de Conser-

vación Guanacaste (ACG, Guanacaste Con-

servation Area), Carlos Hiller Submarine Arts,

Fallas family, Consorcio Primos Titin, Veerle

Roelandt, and Rufford Small Grants.

RESUMEN

Residencia del tiburón toro, Carcharhinus leucas,

(Carcharhiniformes: Carcharhinidae) en

el islote de San Pedrillo, Islas Murciélago,

Pacífico Norte de Costa Rica

Introducción: El tiburón toro (Carcharhinus leucas) es

una especie tropical y subtropical que habita ríos, estuarios

y aguas costeras.

Objetivo: Estudiar la residencia del tiburón toro en

San Perdillo, Islas Murciélago, Área de Conservación

Guanacaste.

Métodos: Durante el período de estudio (junio de 2013 a

febrero de 2015) se marcaron 10 tiburones toro con teleme-

tría acústica en San Pedrillo.

Resultados: los tiburones marcados fueron todos hembras

y fueron detectados en 59 798 ocasiones por el receptor

acústico desplegado en San Pedrillo. Las señales acústi-

cas de los tiburones marcados se recibieron durante un

período total de 1 a 229 días (media = 73.9 ± 71.3 días), y

las últimas detecciones ocurrieron el 9 de enero de 2015.

El índice de residencia de cada tiburón marcado durante

todo el período de seguimiento osciló entre 0.41 y 1.00. La

actividad del tiburón toro mostró un patrón significativo a

lo largo del día en el receptor que se corresponde específi-

camente con el ciclo de luz diario.

Conclusiones: Este estudio concluyó que San Pedrillo es

un sitio de agregación (estación de limpieza) para el tibu-

rón toro, posiblemente relacionado con comportamientos

de reproducción y no de alimentación; y es un sitio crítico

para la especie. Se necesitan más estudios para identificar

áreas de alimentación y cría en el Área de Conservación de

Guanacaste y áreas circundantes.

Palabras clave: Carcharhinus leucas; Guanacaste; marca-

je acústico; telemetría pasiva; sitio de agregación.

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