Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57284, diciembre 2023 (Publicado Nov. 01, 2023)

Bryde’s Whale (Balaenoptera edeni brydei, Artiodactyla: Balaenopteridae)

aggregation area in the Gulf of Chiriqui, Panama

Kristin Rasmussen1*; https://orcid.org/0000-0003-4758-5010

Daniel M. Palacios2, 3; https://orcid.org/0000-0001-7069-7913

1. Panacetacea, 1554 Delaware Ave., St Paul, MN 55118, USA; panamakristin@gmail.com (*Correspondence)

2. Marine Mammal Institute, Oregon State University, Newport, OR 97365, USA; daniel.palacios@oregonstate.edu

3. Department of Fisheries, Wildlife, and Conservation Sciences, Oregon State University, Newport, OR 97365, USA

Received 28-VII-2022. Corrected 23-VIII-2022. Accepted 07-II-2023.

ABSTRACT

Introduction: Even though they occur worldwide in tropical and subtropical waters, Bryde’s whales (Balaenoptera

edeni) are one of the most enigmatic of all the balaenopterid species. Previous research has reported the pres-

ence of Bryde’s whales off the Pacific coast of Panama, but little is known about their behaviors, abundance, and

distribution in these waters.

Objective: We report on an area in the Gulf of Chiriqui, Panama, where Bryde’s whales have regularly been

sighted.

Methods: We conducted small-boat surveys for marine mammals in the Gulf of Chiriqui between 2001 and 2022,

during both the austral (26 300 km) and boreal (4 700 km) winter seasons.

Results: We made 25 sightings of 33 Bryde’s whales. Sightings were made in nine of the years surveyed, and most

were in the austral winter season (92 %). Most sightings were of one animal (80 %), and one sighting was of a

mother-calf-escort trio. The aggregation area appears near the Contreras Islands, where most sightings (84 %)

were made. We have photo-identified 14 individual whales using the dorsal fin. One individual has been sighted

over two years (2014 and 2015), while the remaining have been documented only once. No photographic matches

have been made to other areas.

Conclusions: The persistent use of this aggregation area could indicate it is used for foraging, and the presence

of a calf may indicate the area is also used for reproduction. The one inter-annual resight suggests this area may

be used repeatedly by some of the same animals. Further research is needed off Panama to better understand this

population of Bryde’s whales, its conservation status, and its relationship to the broader eastern tropical Pacific

populations. Expanding the marine protected areas in the Gulf of Chiriqui may be warranted in order to protect

this aggregation area.

Key words: Central America; baleen whales; eastern tropical Pacific; occurrence; photo-identification.

RESUMEN

Área de Agregación de la Ballena de Bryde (Balaenoptera edeni brydei) en el Golfo de Chiriquí, Panamá

Introducción: Aunque la ballena de Bryde (Balaenoptera edeni) tiene una distribución global en aguas tropicales

y subtropicales, la especie es una de las más enigmaticas entre los balaenoptéridos. Observaciones previas han

reportado la presencia de ballenas de Bryde en la costa del Pacífico de Panamá, pero sabemos poco acerca de su

comportamiento, abundancia, y distribución en estas aguas.

Objetivo: Reportamos un área en el golfo de Chiriquí, Panamá, donde la ballena de Bryde ha sido avistada

frecuentemente.

https://doi.org/10.15517/rev.biol.trop..v71iS4.57284

SUPPLEMENT • WHALES

2Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57284, diciembre 2023 (Publicado Nov. 01, 2023)

INTRODUCTION

Bryde’s whales (Balaenoptera edeni Ander-

son, 1878) are one of the most enigmatic

of all the balaentopterid species, despite hav-

ing a worldwide distribution in tropical and

subtropical waters, including in the Pacific,

Atlantic, and Indian Oceans (Kato & Perrin,

2018). Much remains unclear about this spe-

cies, including its taxonomy, distribution, and

migration. Currently there are two subspe-

cies recognized; B. edeni edeni is smaller and

typically found in coastal waters, and B. edeni

brydei is larger and globally distributed (Kato

& Perrin, 2018; Kershaw et al., 2013,). Both

subspecies have been found in the Indian and

Pacific oceans, and B. edeni brydei also has

been found in the Caribbean (Luksenburg et

al., 2015). Unlike other baleen whale species,

Bryde’s whales do not make long annual migra-

tions between cold-water feeding areas and

warm-water breeding areas, but remain in trop-

ical and subtropical waters year-round. How-

ever, some populations have shown evidence of

large-scale movement within this range, while

others appear to be resident (Best, 2001; Kato

& Perrin, 2018; Lagerquist et al., 2017; Murase

et al., 2015). Bryde’s whales are considered

opportunistic feeders and can feed on small

pelagic schooling fish or zooplankton. Different

populations tend to show a preference for one

type of prey depending on geographic location

(Constantine et al., 2018; Kato & Perrin, 2018).

Between 1986 and 2005, large-scale visu-

al surveys in offshore waters of the eastern

tropical Pacific (ETP) documented Bryde’s

whales between 30°N and 15°S (Hamilton et

al., 2009). Additionally, an acoustic study in the

ETP between 1999 and 2001 detected Bryde’s

whale calls at seven different offshore sta-

tions between 12° N and 8° S (Heimlich et al.,

2005). Across the broader eastern Pacific, other

reports of Bryde’s whales include off southern

California (Kerosky et al., 2012; Smultea et al.,

2012), Mexico (Salvadeo et al., 2011; Tershy,

1992; Viloria- Gómora et al., 2021), Nicaragua

(De Weerdt et al., 2021), Costa Rica (May-

Collado et al., 2018), Colombia (Palacios et

al., 2012), Ecuador, including the Galapagos

Islands (Alava et al., 2013; Biggs et al., 2017;

Castro et al., 2017; Palacios & Forney, 2008),

Peru (Clarke & Aguayo, 1965; Ramirez, 1986;

Valdivia et al., 1981), and Chile (Clarke &

Aguayo, 1965; Gallardo et al., 1983; Pastene et

al., 2015). Bryde’s whales have been previously

reported in Panama (May-Collado et al., 2018;

Rasmussen & Palacios, 2013), but little infor-

mation is available from the Gulf of Chiriqui.

Métodos: Realizamos muestreos para mamíferos marinos desde embarcaciones pequeñas en el golfo de Chiriquí

entre el 2001 y el 2022, tanto durante el invierno austral (26 300 km) como el boreal (4 700 km).

Resultados: Registramos 25 avistamientos de 33 ballenas de Bryde. Los avistamientos ocurrieron en nueve de los

años muestreados, la mayoría en el invierno austral (92 %). La mayoría de avistamientos fueron de un animal (80

%), y un avistamiento fue de un trío madre-cría-escolta. El área de agregación ocurre cerca de las islas Contreras,

donde la mayoría de los avistamientos (84 %) fueron registrados. Foto-identificamos 14 individuos usando la aleta

dorsal. Un individuo fué avistado en dos años (2014 y 2015), mientras que el resto solamente ha sido documen-

tado una vez. No se han registrado recapturas fotográficas con otras áreas.

Conclusiones: El uso repetido de ésta área de agregación podría indicar que es usada para alimentación, y la

presencia de un trío madre-cría-escolta también sugiere actividad reproductiva. El único re-avistamiento inte-

rannual sugiere que el área es usada por algunos de los mismos animales. Se necesita más investigación en aguas

panameñas para entender mejor esta población de ballena de Bryde, su estatus de conservación, y su relación

con otras poblaciones del Pacífico tropical oriental. Una expansión de las áreas marinas protegidas en el golfo de

Chiriquí puede ser necesaria para proteger esta población.

Palabras clave: Centroamérica; ballenas de barbas; Pacífico tropical oriental; ocurrencia; foto-identificación.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57284, diciembre 2023 (Publicado Nov. 01, 2023)

This study reports on Bryde’s whales sighted

in the Gulf of Chiriqui from long-term, small-

boat surveys between 2001-2022.

MATERIALS AND METHODS

Study site: The Gulf of Chiriqui lies in the

western part of Panama and is bordered by the

Azuero Peninsula to the east, and Punta Burica

to the west (7°18’ - 8°18’ N & 82°54’ - 81°36’

W; Fig. 1). This gulf is characterized by gener-

ally shallow waters (< 300 m) and many island

groups. Monthly sea surface temperature ranges

between 25 – 29 °C (Randall et al., 2020). How-

ever, like the rest of the ETP, the gulf is subject

to the anomalous effects from the regional El

Nino-Southern Oscillation (ENSO) phenom-

enon, which results in warmer sea surface tem-

peratures (Podestá & Glynn 2001; Randall et

al., 2020; Wang & Fiedler, 2006;). Two protected

areas have been established by the government

of Panama (Fig 1a): Coiba National Park and

its Special Zone of Marine Protection, which

is also a UNESCO World Heritage Site and

includes Coiba Island and the Contreras Islands

(https://whc.unesco.org/en/list/1138/), and the

Gulf of Chiriqui National Marine Park, which

includes the Paridas Islands. The gulf is also

well-known for its use as a breeding area by

two different populations of humpback whale,

Megaptera novaeangliae (Borowski, 1781), one

migrating from feeding areas in the Southern

Fig. 1. A. Minimum convex polygons (MCP) for both survey area (green) and sighting locations (orange), red circles indicate

sighting locations for all Bryde’s whale sightings. The hatched overlays represent marine protected areas, including Gulf of

Chiriqui National Marine Park at the Paridas Islands, and Coiba National Park (right side of Coiba hatched overlay) and its

Special Zone of Marine Protection (left side of overlay). B. Survey effort tracklines and Bryde’s whale sighting locations for

two seasons (blue for boreal winter and red for austral winter). C. Gridded representation of the survey effort in the Gulf of

Chiriqui using a honeycomb grid with 1-km edges. D. Kernel density distribution for Bryde’s whale sightings.

4Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57284, diciembre 2023 (Publicado Nov. 01, 2023)

Hemisphere, and one migrating from feeding

areas in the Northern Hemisphere (Rasmussen

et al., 2007).

Boat surveys: Visual surveys were con-

ducted from a small boat in the Gulf of Chiriqui

between 2001 and 2022, in both the bore-

al winter (January-March) and austral win-

ter (July-September), to correspond with the

breeding seasons of the two humpback whale

populations that use this area (Rasmussen et

al., 2007). Humpback whales were the primary

species targeted, but all marine mammal spe-

cies encountered were documented. Data col-

lected included time, GPS location, number of

animals in the sighting, and behaviors. Surveys

were non-systematic in design and conducted

in waters less than 200 m depth, near coastlines,

island groups, and rocky outcroppings, which

are the preferred humpback whale breeding

habitat (Clapham & Mead, 1999; Rasmussen

& Palacios, 2013). When Bryde’s whales were

encountered, identification photographs of the

right and left sides of the dorsal fin were taken

with a Nikon SLR camera equipped with a tele-

photo lens.

Data analyses: Given the extensive and

non-uniform survey effort, the survey track-

lines were gridded for visual interpretation

using honeycomb cells with 1-km edges with

the XtoolsPro software (https://xtools.pro/) for

ArcMap v. 10.8.2 (Esri, Redlands, CA). Ker-

nel density analysis of the sighting locations

was conducted with ArcMap to characterize

the concentration of Bryde’s whale sightings.

The total survey area and the area used by the

Bryde’s whales were estimated using minimum

convex polygon analysis (MCP) in ArcMap.

RESULTS

We surveyed a total of 31 000 km over 334

days. Most effort (26 300 km and 294 days) was

in the austral winter between 2002 and 2019

(with the exception of 2005 and 2016, when

no effort took place) (Fig. 1b). The remaining

effort (4 700 km and 40 days) was in the boreal

winters of 2001-2003, 2018, and 2022 (Fig. 1b).

Surveys covered most of the gulf, with the

greatest concentration near the island groups

of Secas, Paridas, Ladrones, and Contreras (Fig.

1b and c).

Between 2004 and 2022 we made 25

sightings of 33 Bryde’s whales. Most sightings

(n = 23, 92 %) were in August and Septem-

ber, and two sightings (8 %) were in February

(Fig. 1b). Whales were sighted in nine separate

years (2004, 2007, 2009, 2013-2015, 2018, 2019,

2022), with the most sightings in one year (nine)

occurring in 2014. Most sightings were of single

whales (n = 20, 80 %), three sightings were of

two whales (12 %), and one sighting was of four

whales (4 %). One sighting (4 %) in September

2004 included a mother-calf-escort trio.

Encounter rates (whales seen per 100 km

surveyed) were calculated for both the austral

and boreal seasons to give an index of relative

abundance. Bryde’s whales were seen at a rate

of 0.09 whales/100 km in the austral winter,

and 0.04 whales/100 km in the boreal winter.

For comparison, humpback whales were docu-

mented during these same surveys at a rate of

13.79 whales/100 km in the austral winter and

0.41 whales/100 km in the boreal winter.

All sightings were near the Contreras and

Secas island groups, and one near Coiba Island

(Fig. 1b). All sightings were made in depths

of less than 200 m. Distances to shore ranged

between 1 and 16.1 km (mean = 5.0 km, medi-

an = 2.5 km, SD = 4.3 km).

The kernel density analysis of the sighting

locations revealed the highest concentration

of sightings around the southern Contreras

Islands, and extending to the northwest towards

the Secas Islands (Fig. 1d). The total survey

area, as delineated by a MCP, was estimated

at 11 800 km2, while the MCP of the area of

Bryde’s whale sightings was estimated at 1 200

km2, or 10 % of the survey area (Fig. 1a).

Of the 25 sightings of Bryde’s whales, most

(n = 17, 68 %) were under 20 minutes in dura-

tion, either because the whales were difficult

to follow or due to bad weather. The longest

period we followed a single whale was 1 hour

25 minutes. Most whales exhibited an erratic

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57284, diciembre 2023 (Publicado Nov. 01, 2023)

surfacing pattern, in which the direction of

travel changed between each surface series, and

sometimes within a surface series. Five sight-

ings included close approaches by the whales

to the boat.

We photographed dorsal fins of 19 whales,

of which 14 were of good quality for identifica-

tion purposes. Of the 14, six had distinctive

nicks or shape, and eight were nondescript.

One individual (identification #009) was sight-

ed over two years on 6 September 2014 and

again on 5 September 2015. The estimated dis-

tance between the two sighting locations was 12

km. The remaining 13 whales were identified

only once.

DISCUSSION

In the Gulf of Chiriqui, Bryde’s whales are

seen at a much lower rate (0.09 whales/100

km in the austral winter and 0.04/100 km

in the boreal winter) than humpback whales

(13.79/100 km in the austral winter and

0.41/100 km in the boreal winter). The results

of the kernel density estimate as well as the

MCP of the aggregation area both also indicate

that despite the extensive survey effort, Bryde’s

whales are more likely to be found near the

Contreras and Secas island groups than any-

where else in the Gulf of Chiriqui, regardless of

the season or year. Such a persistent aggrega-

tion area suggests this may be a localized area

of elevated productivity where Bryde’s whales

are foraging. The Contreras Islands are his-

torically known by local fishers to be one of the

most productive areas in the Gulf of Chiriqui,

including small schooling fish (L. Bernal, per-

sonal communication, 6 May 2022), although

this area is currently protected and no fishing

is allowed within the National Park boundaries

(see Fig. 1a). Examples of Bryde’s whale feeding

areas described less than 10 km to shore include

in the Galapagos Islands, Ecuador (Biggs et

al., 2017), the Beibu Gulf, China (Chen et al.,

2019), and the Gulf of California, Mexico (Ter-

shy, 1992). Further study is needed specifically

in the Contreras and Secas Islands to assess the

oceanographic and bathymetric conditions that

may lead to a localized area of high productivity

(Wingfield et al., 2011).

The September sighting of a mother-calf-

escort trio in Chiriqui could indicate that in

addition to this being a feeding area, it may also

be an area used for reproduction. Mother-calf

pairs have been seen in an area associated with

foraging in the Galapagos Islands (Biggs et al.,

2017), suggesting it is an area where both forag-

ing and breeding behaviors both occur. Further

study would also address the extent to which

Bryde’s whales are using Chiriqui for reproduc-

tive purposes in addition to foraging.

The seasonality of Bryde’s whales in this

area is somewhat unclear. This study reports

sightings in February, August and Septem-

ber, but there are also anecdotal reports from

residents and naturalists in Chiriqui from

November and December (L. Klein, V. Wil-

son, personal communication, 19 April 2022).

Between 2013-2021 seven strandings of Bryde’s

whales were reported off Panama in February,

March, April, August and December, although

none of these were in Chiriqui (L. Trejos-Lasso,

personal communication, 29 April 2022). A

current study in Chiriqui using continuously

sampling bottom-mounted hydrophones could

add information on the seasonality of Bryde’s

whales in the area (L. May-Collado, personal

communication, 4 May, 2022).

While the re-encounter of one of our pho-

to-identified whales to the same area a year

later could suggest that the same animals may

be using this area year after year, further study

is necessary to determine the extent of site fidel-

ity. Other studies have reported varying degrees

of site fidelity for this species (Athayde et al.

2020; Figueiredo et al. 2014, Lodi et al. 2015,

Tezanos-Pinto et al. 2017,). There is no infor-

mation on whether this population is strictly

coastal or may also move to offshore areas.

Different populations of Bryde’s whales have

shown a variety of seasonal movement patterns.

Two distinct populations of Bryde’s whales in

South Africa are an example of this, with one,

the Southeast Atlantic population, migrating

between the equator and 34° S, while the South

6Revista de Biología Tropical, ISSN: 2215-2075 Vol. 71(S4): e57284, diciembre 2023 (Publicado Nov. 01, 2023)

African coastal population is resident year-

round (Best, 2001; Constantine et al., 2018).

A previous study compared our photo-

identification catalog to 51 individually identi-

fied Bryde’s whales from Ecuador (both the

continent and the Galapagos) and Peru, and

found no matches (Castro et al., 2017). Fur-

ther comparisons among regional photo-ID

catalogs as well as satellite tagging could yield

more information about the movements of

these whales.

The taxonomy of this population and how

it relates to other Bryde’s whale populations in

the ETP is also worthy of investigation. Genetic

sampling will help determine the taxonomic

status as well as help to resolve some of the

uncertainty of this species on a global level

(Constantine et al., 2018). A previous genetic

study determined that Bryde’s whales off Brazil,

Chile, and Peru were the B. brydei form (Pas-

tene et al., 2015). Further genetic sampling is

needed not only off Panama, but in other areas

of the ETP as well.

While the Gulf of Chiriqui does contain

some marine protected areas (MPAs), extend-

ing some of these MPAs to better include

the Bryde’s whale aggregation area we have

identified here may be warranted. The gulf

is an important breeding area for humpback

whales from the southeast Pacific (Rasmussen

& Palacios, 2013) and is also used by hump-

back whales from the Central America Dis-

tinct Population Segment, which is currently

listed as endangered by the USA government

(Rasmussen et al., 2011, Rasmussen & Pala-

cios, 2020; National and Oceanic Atmospheric

Administration, 2016). In comparison with

humpback whales, Bryde’s whales are seen far

less frequently in the Gulf of Chiriqui, yet they

have been consistently sighted since 2004 and

are concentrated in a relatively small area of the

gulf. Globally, the conservation status of Bryde’s

whales is considered of “Least Concern” by the

IUCN (Cooke & Brownell, 2018). However, the

restricted distribution and low encounter rates

in the Gulf of Chiriqui suggests that either this

is a small and localized population, or that this

habitat supports a small number of visiting

individuals. This population could be particu-

larly vulnerable due to its restricted distribu-

tion within the gulf, although this restricted

distribution is well-suited for conservation pur-

poses as it lends itself to a clear designation of

a protected area. While some of the Bryde’s

whale aggregation area (as determined by the

MCP analysis) is within the Coiba National

Park MPA, some if it is outside the protected

zone (Fig. 1a). Therefore, it may be advisable

to expand this MPA to include all of the area

where Bryde’s whales are sighted. Connecting

it with the Gulf of Chiriqui Marine Park in

the Paridas Islands would create a continuous

protected corridor which could benefit not only

Bryde’s whales, but other marine species as well.

Ethical statement: the 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 fol-

lowed all pertinent ethical and legal procedures

and requirements. All financial sources are fully

and clearly stated in the acknowledgements sec-

tion. A signed document has been filed in the

journal archives.

Author Contribution: KR collected data

in the field, conceptualized and conducted data

analysis, and drafted the manuscript. DMP

collected data in the field, conceptualized and

assisted with data analysis, and contributed to

the manuscript.

ACKNOWLEDGMENTS

Funding for this project was provided by

the Islas Secas Foundation, Cascadia Research

Collective, the Earl and Ethel Myers Oceano-

graphic Trust, and The Packard Foundation.

Assistance in the field was provided by Luis

Bernal, Betzi Perez-Ortega, Ursula Gonzalez-

Peral, Tomas Bernal, Jose David Palacios, Laura

May-Collado, Matthew Leslie, Chelina Batista,

Jose Julio Casas, Ester Quintana, Lissettte Tre-

jos-Lasso, Marco Tulio-Saborio, and numerous

student interns. Linda Klein, Michael Klein,

Jim Matlock, George Ravenscroft, and the Islas

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 71(S4): e57284, diciembre 2023 (Publicado Nov. 01, 2023)

Secas Resort provided logistical assistance. We

thank these people and organizations.

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