Marine Mammals and Predators in Costa Rica

Expedition Briefing


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The Research

Golfo Dulce, a fiord-like embayment on the southern Pacific coast of Costa Rica, provides an ideal habitat for marine top predators such as cetaceans (whales and dolphins) and sharks. (Oviedo 2007, Oviedo & Solis 2008, Oviedo et al. 2015, 2018 Pacheco-Polanco et al. 2015). This region is among the best preserved marine habitats in the Osa Peninsula. However, tourism, development, and other human activities are encroaching on this critical habitat and the many species that depend on it.

There is mounting evidence that Marine Protected Areas (MPAs) increase the health and abundance of key marine species, and are therefore considered to be one of the best ways to safeguard the health of coastal ecosystems. But to designate Golfo Dulce as an MPA, scientists first need to understand and demonstrate the importance of this critical ecosystem.

For more than 10 years, scientists have gathered data on species such as migratory humpback whales, and resident bottlenose and pantropical spotted dolphins, in this marine habitat to evaluate their abundance and distribution. Now, they need to deepen this understanding within an ecosystem-based context and explore the ecological role of other species within a major predatory guild. We need to understand the non-mammal predatory structure of the ecosystem in several aspects; therefore, we seek to answer initially the basic questions of what are those predators, where we find them and when are they most abundant.

The preservation of the beauty and well-being of Golfo Dulce’s marine ecosystem benefits everyone—it can help local agencies manage tourism in the area in a sustainable way, which will generate income for the local community and give tourists the opportunity to learn about one of Costa Rica’s great treasures without destroying it. The research conducted by Earthwatch teams will help scientists to assess the importance of this marine habitat and design management plans to protect it.

Research Aims

Unlike in the open ocean, the confined nature of Golfo Dulce makes it possible for us to observe whales and dolphins at the surface for extended periods of time. Through our research, we seek to assess these species’ population sizes and structures, their distribution and habitat preferences, and their behavioral patterns and the ways in which they utilize this habitat. This information will help us develop conservation plans to protect the marine biodiversity in the gulf in the future. Additionally, Golfo Dulce being a low oxygen basin (anoxic), where marine predators thrive, will help us to understand the complex dynamic of possible scenarios of climatic changes driving the expansion of low oxygen zones in the Pacific Ocean and how upper trophic level organism would respond under this future potential environmental disruption. In other words Golfo Dulce is a small-scale model of what will come in the future for tropical marine ecosystems.

Objective 1: Increase the biological information on coastal cetaceans’ critical habitat in Golfo Dulce through the use behavior sampling, and photo-identification. Specifically, this objective seeks to:

  • Document changes in habitat use of known areas of critical importance for dolphins such as foraging areas, breeding and calving habitats, and other areas.
  • Document changes in habitat use within key areas for calving and breeding humpback whales

Objective 2: Deepen the knowledge of the food web that exists in Golfo Dulce to better understand the ecological role of species within a trophic web. This includes assessing which species of sharks and what life stage (adults, juveniles, pups) are present during different times of the year, and what their target prey tend to be.

Objective 3: To assess the composition of the marine predatory guild and prey base that makes up the entire food web of Golfo Dulce, both along coastal habitat such as the mangrove and in the inner basin.

How You Will Help

Our research team of three resident marine biologists and two students will lead you in all research tasks, including observing cetaceans, making photo identifications, recording vocalizations and collecting data. When you first arrive at camp, you’ll receive an orientation and intensive training on research methods, and during the days that follow, you’ll work in small teams or pairs on the following tasks:

  • Observing Cetacean Behavior. We will travel on board a 27-foot (nine-meter) motorboat a few days per team to make observations of whales and dolphins. You’ll record the position of cetaceans and any boats we spot (to help us assess how vessel traffic affects cetacean behavior) with a handheld GPS unit. You’ll also record the size, composition, and behavior of the dolphin and whale groups we see. And at the beginning and end of each survey period, as well as every half-hour throughout it, you’ll record environmental data like water surface temperature and sea condition. On excellent sea condition, you will also help in recording cetaceans’ vocal behavior using a hydrophone. Wildlife sighting are extremely likely, but not guaranteed. While the chance to seeing dolphins is extremely high, whales are a bit less predictable with respect to the timing of their arrivals. We will focus of studying the whales from the southern Pacific. Generally they arrive in early August and depart in mid-October to their foraging grounds. Migration patterns vary and sighting during these months cannot be guaranteed.
  • Documenting the Trophic Web in Golfo Dulce. You’ll help record and describe the species in multi-predator assemblages. We will observe aggregations of schooling fish and predators such as dolphins, seabirds, and sharks. We will collect data on species composition of the aggregations, the length of the event, and the location. You will also help sample the occurrence of other predators using hook and line. This sampling will take place at dawn, dusk and after dinnertime, and you will identify predators by species and take measurements to determine age.
  • Fishing Surveys.
    • Set long lines out by boat at dusk, returning to El Tucan for dinner. After dinner and once “full dark”, you’ll head back out on the boat to check the lines, identifying and measuring all sharks and other major predatory fish captures before releasing back into the gulf.
    • Some caught fish are used to get samples of stomach content, so there will be the opportunity to help doing necropsies and tissue sampling collection.
  • Sorting Photos and Identifying Individual Cetaceans. You’ll then help us sort photos by species and attempt to match individuals we’ve sighted with photos of individuals in our photo ID catalog. We use photo ID management software for the matching process, which displays the encounter history of each individual we’ve already identified, along with a high-quality photo of the dorsal fin, which clearly shows natural marks such as notches and nicks. These marks help distinguish between individuals.
  • Working with the Local Community: You may help present to and develop and run educational activities for local schools and other community stakeholders, giving you the opportunity to get to know some of the people who live around Golfo Dulce.

Note: All teams will work with dolphins, but only some teams will work with whales. Whales from the southern Pacific generally arrive in early August and depart in mid-October. These are general patterns and vary from season to season. The team has observed much more variation each year, and whale sightings are not guaranteed.

Life in the Field

After breakfast, the team will begin their work for the day. Each day’s tasks will rotate between dolphin and whale surveys, trophic web work and sorting and cataloging photos for individual identification. For whale and dolphin surveys, the team will usually establish a priority species of the day and focus on finding that species first. The team will change focus to other species throughout the day as time and conditions allow. Photographs for photo-ID and behavior-acoustic sampling are conducted with each of the focus species.

Lunch is eaten on the boat or in the field. You may help us carry light equipment to the boat and load it on. Photo-identification sessions will take approximately two hours, though groups will be on the boat for up to 5 hours. Everyone on the boat will have a specific task, such as handling video and photo equipment, recording instrument readings, such as GPS coordinates or keeping track of dolphins’ babies, specifically those of identified resident females. Always ask if you need to switch tasks or rest.

We will also spend some time on land. We will conduct surveys by hook and line for major predatory fish such as sharks, barracudas, and tuna. This includes baiting the hook and assembling the rig.

Once we are back to the camp we check equipment and store audios, footage and photos collected during the surveys. There will be free time to rest and get out of the sun in the afternoon, followed by data entry and photo ID matching in the evening. The team will eat dinner together, where a discussion on the day’s results and events and the impact on the current research-conservation project is encouraged.

You’re most likely to encounter the target whale and dolphin populations during the following times:

Spotted Dolphins: year-round

Bottlenose Dolphins: year-round

Humpback Whales (Southeast Pacific Population): early August through mid October; peak presence in August and September

  • Day 1: Arrival; tour of our home base, El Tucan; settling in; orientation and training
  • Day 2: Training on dolphin and whale behavior sampling and dolphin photo-identification (including both fieldwork and lab work at camp) and/or possible dolphin survey
  • Day 3: Boat survey and photo-ID lab work at camp; Predatory Fish Survey
  • Day 4: Boat survey and photo-ID lab work at camp; Predatory Fish Survey
  • Day 5: Boat Survey and Information logging at camp; Predatory Fish Survey
  • Day 6: Boat survey and photo-ID lab work at camp; possible cultural activity
  • Day 7: Boat survey and Photo-ID lab work at camp; Predatory Fish Survey
  • Day 8: Time off to explore or photo-ID lab work at camp
  • Day 9: Departure


Accommodations and Food

* Please note that not every expedition has couples’ or single's accommodations available. Please call or email Earthwatch to check for availability prior to reserving your space(s) on the team.


Volunteers will stay at a locally run hostel, Hostel del Mar. There will be two to four people per room and shared bathrooms. People of the same gender will share rooms. The hostel provides sheets, pillows, blankets, and a bath towel (however, bringing an extra one will be wise).

* Earthwatch will honor each person’s assertion of gender identity, respectfully and without judgement. For both teen and adult teams, where logistics dictate single-sex accommodations or other facilities, participant placements will be made in accordance with the gender identity the participant specified on their Earthwatch Participant form and/or preferences indicated in discussions with Earthwatch.


The accommodations have shared bathrooms, which include showers and flush toilets.

There is no bathroom on the boat. The boat is small and does not have an inside cabin. There will be a bucket available for bathroom use in the event someone cannot wait for land. This is standard for small boats and routine for the crew. Everyone aboard will make sure to turn away, and provide as much privacy as possible.


Electricity is 120 volts, 60 hertz, Type A and Type B plugs (as in the U.S.). You may charge electronic equipment, but please avoid plugging in many appliances at once.


While this is a remote area, there is cell reception at the cabins. Please check with your service provider regarding coverage in Costa Rica. The nearest town, Golfito has payphones available, but they do not accept prepaid calling cards from foreign countries. If you’d like to make calls during your stay, you should pick up an international prepaid card when you arrive in Costa Rica. Golfito also has a bank and several Internet cafés. The U.S. standard voltage used for small appliances, hair dryers, electronic equipment, etc. is 120 volts, 60Hz, supplied through type A or B sockets.

Personal communication with outsiders is not always possible while participating in an expedition. Earthwatch encourages volunteers to minimize outgoing calls and immerse themselves in the experience; likewise, family and friends should restrict calls to urgent messages only. However, in case of emergency there will be a landline available.


We’ll depart from Golfito’s pier for conducting research activities on the boat and travel to different areas in Golfo Dulce.


You’ll enjoy typical Costa Rican fare on this expedition, including rice and black beans, meat, vegetables, fruit, coffee, and juice. The team will eat breakfast and dinner together in the communal area at the hostel, and will pack lunches to take into the field each day. The cooks will do all meal prep.

The following are examples of foods you may find in the field. Variety depends on availability. We appreciate your flexibility.

  • Breakfast: Gallo pinto (rice and beans, the best in the country), plantains, fresh cheese, eggs
  • Lunch: Sandwiches, fruit (e.g., watermelon, pineapple, bananas)
  • Dinner: Costa Rican-style rice and chicken, salad, pasta with homemade sauce
  • Snacks: Each breakfast and dinner will be accompanied by amazing fresh, local fruit juice. The local grocery store is always well stocked with ice cream at our request; the local brand Dos Pinos is very good. You will have the opportunity to buy snacks during the day.
  • Beverages: We keep a container of filtered water exclusively for the use of participants. We refill the bottle regularly. We encourage constant hydration and water consumption. You’ll sweat a lot even when not exerting yourself, so it’s a good idea to replenish essential electrolytes by drinking a sports drink (e.g. Gatorade) at least once a day.

Please alert Earthwatch to any special dietary requirements (e.g., diabetes, lactose intolerance, nut or other food allergies, vegetarian or vegan diets) as soon as possible, and note them in the space provided on your volunteer forms.

This expedition can accommodate most special diets with advance notice. We can provide full options for vegetarians and even vegans, some other dietary requirements such as gluten free food might be a challenge in Golfo Dulce and Osa Peninsula in general. However, if volunteers, due to very specific diets, bring food complements we gladly assist with special meals preparation.

Project Conditions

The camp is on flat terrain, but any hikes (optional) will likely be located in hilly areas. The site is about 10 meters above sea level.

The general climate throughout the year is humid tropical, with a rainy season that extends from May to early November. The dry season runs from mid-November to April, but even during this time period, it’s still very humid with regular afternoon showers.


For weather and region-specific information, please visit and search for your project location.

Essential Eligibility Requirements

All participants must be able to:

  • Take an active role in your own safety by recognizing and avoiding hazards if and when they arise (including, but not limited to, those described in Earthwatch materials and safety briefings). Comply with project staff instructions and recommended safety measures at all times.
  • Be able to effectively communicate to the staff if you are experiencing distress or need assistance.
  • Be comfortable being surrounded by a language and/or culture that is different from your own.
  • Be able to get along with a variety of people from different backgrounds and ages, often in close proximity, for the duration of your team.
  • Follow verbal and/or visual instructions independently or with the assistance of a companion.
  • Enjoy being outdoors most of the day in variable weather, in the potential presence of wild animals and insects.
  • Tolerate 30°C (85°F) heat and high humidity levels.
  • Spend long hours sitting on a boat (some may experience seasickness) for an average of 5 hours per day with only access to a bucket on the boat to relieve yourself for 3–4 days per team.
  • Search for dolphin signs (jumps, unusual ripples in the water, movements) on the surface of the water, while moving aboard the survey boat and on a screen while sitting at a ground station.
  • Carry personal daily supplies such as lunch, water, and some small field equipment.
  • Climb into and down out of a minibus and ride, seated with the seatbelt fastened, for a total of about 1.5 hours a day.

Health and Safety


We have a VHF radio on the boat, mobile phones and two-way radios in some areas, and a landline phone at the cabins. Project staff members are not medical professionals.

Earthwatch has a 24-hour, 7-day-a-week emergency hotline number. Someone is always on call to respond to messages that come into our live answering service.


Please be sure your routine immunizations are up-to-date (for example: diphtheria, pertussis, tetanus, polio, measles, mumps, rubella and varicella) and you have the appropriate vaccinations for your travel destination. Medical decisions are the responsibility of each volunteer and his or her doctor. Visit the Center for Disease Control and Prevention or the World Health Organization for guidance on immunizations.

If traveling from countries or region where yellow fever is endemic, you must have a certificate of vaccination.

Project Risks and Precautions


We may encounter poor road conditions and landslides. Only qualified drivers will transport volunteers in project vehicles; we ensure project vehicles are well maintained. Seat belts must be worn at all times. Volunteers are not permitted to drive.


You’ll likely traverse uneven terrain and hike uphill in humid tropical conditions; there is a risk of sprains, strains, or breaks due to falling or tripping. You should never walk ahead of the local guide and should follow the guide’s instructions. Wear comfortable, closed-toed shoes when walking. At night, carry a personal headlamp or flashlight.


Poisonous snakes live in the area, but we have never had a snakebite incident. You’ll likely encounter many insects; wear long-sleeved shirts and long pants and apply insect repellent frequently to avoid bites. Those with insect allergies should bring the proper emergency treatment and inform staff of the problem and the location of the treatment.

Working with Sharks

Working with sharks alongside a boat is inherently dangerous. All sharks we work with are hooked in the mouth and are secured by their tails prior to the workup. Teams will be heavily supervised during this activity and will not touch sharks forward of their dorsal fins. Staff will train you to identify dangerous species and to avoid touching any organisms.

Working at Night

Conducting the predatory fish surveys may involve working after dark, because that is when the animals are active. These surveys are conducted from the boat, very close to the accommodations—about 20 meters away. The boat is equipped with 2-way VHF radios and lights. Lights will be used only in the event of an emergency. Minimal light is required so the animals are not disturbed. The surveys are conducted in an area free of rocks and other collision hazards. It is recommended that you bring a headlamp with an infrared light.


Dehydration, heat exhaustion, sunburn, and other heat-related illnesses can occur, but you can protect yourself by drinking sufficient water, wearing high-SPF sunscreen, and wearing appropriate clothing. Dehydration from sweating can be a problem; please bring your own water bottles that you can easily carry and refill them with electrolyte packets. Because of the high humidity, people who use a hearing aid device may find it doesn’t work properly. Consider purchasing a hearing aid dehumidifier.

Project Tasks/Equipment

Tripping over ropes on the boat or injury from equipment is possible. You will receive a full safety briefing on arrival; please follow all staff instructions. A first aid kit will be available on the boat.

Working on a Boat

There is a risk of sprains, strains, or breaks from stepping in and out of the boat, or during adverse sea conditions. We will use a ladder when entering and exiting the boat. Hazards may result from falling overboard. Some volunteers may get seasick; please bring seasickness medication as a precaution. Boarding and stepping out of an inflatable craft and/or sitting onboard when the sea is choppy may cause problems for those with mobility or spinal conditions. These volunteers should carefully consider participation on the project. In addition, volunteers with back, knee, and hip problems, or pregnant women, may face difficulties or discomfort not only when they step on board and leave the boat, but also during navigation under choppy sea conditions. Life jackets and appropriate footwear must be worn at all times while on deck and the vessel is underway.

Personal Security

Avoid areas designated as off limits by project staff.


Swimming may be possible during recreational time, as long as volunteers are competent swimmers and project staff has vetted the location. You may only swim in known, safe environments, close to the boat while it is at anchor, and under the supervision of project staff. Do not swim alone.

Distance from Medical Care

It may take an hour or more to arrange transport and reach the hospital. If you have a chronic condition which could require immediate medical care (e.g., heart conditions, kidney problems, severe asthma, etc.), or if you are pregnant, please discuss your participation on this expedition with your physician.


Diseases found in Costa Rica may include malaria, dengue fever, Zika, tuberculosis, filariasis, leishmaniasis, onchocerciasis, trypanosomiasis, schistosomiasis, strongyloidiasis, hepatitis, leptospirosis, chikungunya, and typhoid. Please see the U.S. Centers for Disease Control and Prevention ( or the World Health Organization ( websites for more information on these conditions and how to avoid them. You can decrease your risk of most diseases above by avoiding mosquito bites, practicing good hygiene, and drinking only bottled or filtered water when appropriate. If you feel ill once you return from your trip, make sure you inform your doctor that you have recently returned from a tropical region. A note on vaccinations and treatment: Malaria is not present at the project area.

Travel Planning


Golfito Airport, Golfito, Costa Rica

* Additional information will be provided by Earthwatch to meet your team. Please do not book travel arrangements such as flights until you have received additional information from Earthwatch.


Earthwatch strongly recommends that travelers investigate their destination prior to departure. Familiarity with the destination’s entry/exit requirements, visas, local laws, and customs can go a long way to ensuring smooth travel. The U.S. Department of State's Traveler’s Checklist and Destination Guides are helpful resources. For LGBTI travelers, the U.S. Department of State's LGBTI Travelers page contains many useful tips and links.


Entry visa requirements differ by country of origin, layover, and destination, and do change unexpectedly. For this reason, please confirm your visa requirements at the time of booking and, again, 90 days prior to travel. Please apply early for your visa (we recommend starting 6 months prior to the start of your expedition). Refunds will not be made for volunteers cancelling due to not obtaining their visa in time to meet the team at the rendezvous. You can find up to date visa requirements at the following website:

If a visa is required, participants should apply for a TOURIST visa. Please note that obtaining a visa can take weeks or even months. We strongly recommend using a visa agency, which can both expedite and simplify the process.

Generally, passports must be valid for at least six months from the date of entry and a return ticket is required.


  • Oviedo Lenin. 2007. Dolphin sympatric ecology in a tropical fjord: habitat partitioning by bathymetry and topography as a strategy to coexist. Journal of the Marine Biological Association. U.K. 87: 1327–1335.
  • Oviedo, Lenin et al. 2008. “The song of the southeast pacific humpback whale (Megaptera novaeangliae) off Las Perlas Archipelago, Panama: preliminary characterization.” Aquatic Mammals. 34: 458-463
  • Oviedo, Lenin and Mauricio Solis. 2008. “Underwater topography determines critical breeding habitat for humpback whales near Osa Peninsula, Costa Rica: implications for Marine Protected Areas.” Revista de Biología Tropical. 56(2): 591-602
  • Márquez-Artavia, Amaru et al. 2012. “The utilization distribution of humpback whales in Golfo Dulce, Costa Rica.” IWC/SC/64/O15. Paper presented at the 64th International Whaling Commision Meeting in Panama, 2012.
  • Bessensen, Brooke. 2015. “Occurrence and distribution patterns of several marine vertebrates in Golfo Dulce Costa Rica.” Osa Conservation Technical Report. (Provides good insight into marine macrofauna in Golfo Dulce).
  • David Herra-Miranda, Oviedo, L., Pacheco-Polanco, J.D. and M. Iñiguez. 2015. Spatial analysis of coastal cetaceans’ critical habitats in Golfo Dulce, Costa Rica: considerations for a marina construction project. IWC/66a/SC/E9. Paper presented at the 66th International Whaling Commision Meeting in San Diego, California 2015.
  • Oviedo, L. Fernandez, Marc., Herra-Miranda, David., Pacheco-Polanco, J.D., Hernandez Camacho, C and D. Aurioles. 2018. Habitat partitioning mediates the coexistence of sympatric dolphins in a tropical fjord-like embayment. Journal of Mammalogy.
  • Kricher, John. A Neotropical Companion. 2nd ed. Princeton, N.J.: Princeton University Press, 1999. (The best book on the beauty of the tropical rainforest.)
  • Hoyt, Erich. Seasons of the Whale. Moray, Scotland: Colin Baxter, 1998. (The best book on the life of the humpback whale.)
  • Shirihai, Hadoram and Brett Jarrett. 2006. Whales, Dolphins, and Other Marine Mammals of the World. Princeton, N.J.: Princeton University Press.
  • Folkens, Pieter A. 2002. Guide to Marine Mammals of the World. New York: Knopf.
  • Garrigues, Richard and Robert Dean. 2007. The birds of Costa Rica: A Field Guide. Ithaca, N.Y.: Cornell University Press.
  • Oviedo, L. (2007). Dolphin sympatric ecology in a tropical fjord: habitat partitioning by bathymetry and topography as a strategy to coexist. Journal of Marine Biological Association of the United Kingdom 87, 1-9.
  • Oviedo L. and M. Solis. (2008) Underwater topography determines critical breeding habitat for humpback whales near Osa Peninsula, Costa Rica: implications for Marine Protected Areas. Revista de Biología Tropical 56, 591-602.
  • Oviedo, L. Herra-Miranda, D., Pacheco-Polanco, D., Figgener, C. Marquez-Artavia, A., Quirós Pereira, W. and M. Iñiguez. (2015). Diversidad de cetáceos en el paisaje marino-costeros de Golfo Dulce, Península de Osa, Costa Rica. Revista de Biología Tropical, 63 (2), 395-406.
  • Oviedo, L. Fernandez, Marc., Herra-Miranda, David., Pacheco-Polanco, J.D., Hernandez Camacho, C and D. Aurioles. 2018. Habitat partitioning mediates the coexistence of sympatric dolphins in a tropical fjord-like embayment. Journal of Mammalogy