Marine Conservation, Science and Research

Osa Conservation Supports Research in Golfo Dulce: Drawing Conclusions

Mogos Islands mark the highest waters of Golfo Dulce.

By Brooke Bessesen

While Jorge and I both loved working on the water, the results of our research brought the greatest rewards. Golfo Dulce is a true bio-gem—one of Costa Rica’s preeminent riches. Several hundred Green sea turtles, critically endangered Hawksbill sea turtles, Olive Ridley sea turtles and (reportedly) Pacific Leatherback sea turtles, rest, feed, mate and nest in the gulf. A rare xanthic colony of pelagic sea snakes resides around the inner basin. Both Northern and Southern Hemisphere Humpback whales enter the inlet to give birth and possibly provide sanctuary for young calves. Whale sharks aggregate in Golfo Dulce. Resident dolphins and other toothed cetaceans breed and raise offspring. Scalloped hammerhead sharks are born there and needlefish spawn. What a remarkably vibrant bionetwork!

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Community Outreach, Marine Conservation

Save the Gulfo Dulce: A firsthand account

Luis Daniel Montero is a kayak tour guide and a local activist

Luis Daniel Montero is a 22-year-old kayak tour guide and volunteer for ASCONA (Asociacion De Servicio Comunitario Nacional y Ambiental), a local non-governmental organization dedicated to community service and environmental conservation on the Osa Peninsula.

Along with a few other ASCONA volunteers, Daniel, as he prefers to be called, is part of an extremely passionate group of activists protesting an American business-owner’s proposal for a large marina development project on the Gulfo Dulce, a proposal met with considerable opposition among Osa residents and various conservationists on and around the peninsula.
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Marine Conservation, Science and Research

Osa Conservation Supports Research in Golfo Dulce: More Species, More Understanding

By Brooke Bessesen

The name “Brown pelican” belies the attractive hues of a mature bird.

I’m sure it comes as no surprise that during our 400+ hours of observation in Golfo Dulce, Jorge and I witnessed an astonishing array of marine life. Indeed, we were astounded by the intense biodiversity revealed to us during our research. In addition to the animals I’ve already blogged about in this series, many more are worth mentioning. Some were officially documented, others were not, but all helped define our emerging portrait of Golfo Dulce.

Brown pelicans (Pelecanus occidentalis) are commonly seen in Golfo Dulce and we located a year-round communal roosting area along the banks of Piedras Blancas National Park in the upper half of Golfo Dulce. We saw many other marine birds, too, including Brown boobies, magnificent frigates, osprey, several species of gulls, terns, swallows, herons, ibis and dozens more wading and estuary birds.

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Marine Conservation, Science and Research

Osa Conservation Supports Research in Golfo Dulce: Different kinds of dolphins

A video still of a Pseudorca, or false killer whale, in Golfo Dulce

Brooke Bessesen conducted Marine research at the Osa in 2010 and 2011 as a recipient of the Greg Gund Memorial Fellowship. Check out her Golfo Dulce report on our website.

Jorge and I were always thrilled to see dolphins, as they are icons of the sea. Luckily, sightings were relatively common (only sea turtles were seen more frequently) and these graceful cetaceans graced our bow almost every day we were on the water. We observed many dolphin behaviors: foraging and traveling, mating and calf care, spyhopping and playing. But, of course, dolphins are not all same.

The most common delphinids seen in Golfo Dulce were Bottlenose dolphins (Turciops truncatus) followed by Spotted dolphins (Stenella attennata). Even though some Spotted dolphins don’t have spots, these two species are fairly easy to tell apart. Spotted dolphins are smaller in body size and have distinctly sickle-shaped dorsal fins. There are behavioral differences, too.

Most of the Bottlenose dolphins in Golfo Dulce appear residential and some even seem to show fidelity to certain parts of the embayment. This species tends to hang out more coastally, especially near river outlets, sometimes chasing ballyhoo and needlefish at the surface. While they occasionally converged into congregations of five to 15, the Bottlenose dolphins were usually seen in smaller groups of two or three.

Spotted dolphinsmigrate in and out of Golfo Dulce, generally using the deeper middle waters of the inlet. The average

A young spotted dolphin speeds along next to our research vessel

group recorded during our survey was five to 60 individuals; however, we recorded several sightings of scattered herds estimated to include 100 to 500 individuals. At times large groups of these gregarious cetaceans could be seen playfully flinging themselves into the air, a show-stopping riot of activity.

A sighting of False killer whales (Pseudorca crassidens) was also made during our study period while aboard the vessel of Project Golfo Dulce Wildlife. We followed about 30 individuals, adults and at least one calf, as they traveling and foraging between Sándalo and Playa Blanca in the upper half of the gulf.

It is also interesting to note that Spinner dolphins (Stenella longirostris) and Short-beaked common dolphins (Delphinus delphis) have been reported inside Golfo Dulce.

A playful Bottlenose dolphin leaps into the air (insert shows the shape of a Bottlenose dorsal).

Dolphins are arguably the most delightful animals to watch. While seeing them is always a thrill, it’s even more exciting to be able to distinguish the species and have enough knowledge about behavior to fully enjoy their aquatic antics.

Marine Conservation, Science and Research

Osa Conservation Supports Research in Golfo Dulce: So Many Sea Turtles!

Side by side, you can begin to see the characteristics that visibly differentiate the three sea turtle species we documented inside Golfo Dulce.

When we began our research, nobody expected us to find very many sea turtles inside Golfo Dulce — most sea turtle activity was thought to occur on the Pacific side of the Osa Peninsula. It turned out that chelonids were the most frequently seen family of animals, accounting for 38 percent of our total sightings. Discovering such significant numbers of sea turtles was one of our most important findings. Sadly, fishermen with many years of experience in Golfo Dulce say the sea turtles there have declined at least 30 percent in recent years.

Jorge and I documented three species: Pacific Black sea turtles, still commonly referred to as “Greens” (Chelonia mydas agassizii), Olive Ridley sea turtles (Lepidochelys olivacea) and Hawksbill sea turtles (Eretmochelys imbricata). Locals also reported seeing near-extinct Pacific Leatherback sea turtles (Dermochelys coriacea) inside Golfo Dulce. That’s four endangered species of sea turtles utilizing the embayment. Amazing!

Our biseasonal data show Golfo Dulce to be a year-round feeding and breeding area for endangered Green sea turtles. We logged over a hundred sightings of them between both surveys. This species, by far the most common, was usually observed in the upper regions of the gulf resting at the sea surface. But we also documented Green sea turtles mating in all four quadrants of the inlet, so their use of the fiord waters appears widespread.

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Marine Conservation, Science and Research

Osa Conservation Supports Research in Golfo Dulce: Photo-identification of Bottlenose dolphins

Dolphin B43 shown alongside a rendered outline of its dorsal fin. We saw this individual five times.

An unexpected but delightful result of our survey work in Golfo Dulce was the identification of about 80 individual Bottlenose dolphins (Turciops truncatus), some of which can be seen in the Appendix of my 2010 report.

How does one go about identifying dolphins? Well, pioneering biologists studying various species discovered ingenious ways to distinguish individuals. Jaguars have unique spots. Gorillas have unique nose prints. Dolphins have unique dorsal fins. By examining the shape, natural markings, scars and trailing edge, a dorsal may appear as distinct as a fingerprint. Of course dolphins don’t sit quietly at the surface while you study the intricacies of their dorsal patterns, so ID work is best done through photos. Luckily, we managed to get photographs for almost 90 percent of our dolphin sightings.

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