Underwater Cameras to Study Sharks in the Galapagos Islands

Dr. Pelayo Salinas de León with the DOVs underwater camera system at Darwin’s Arch.

Written in collaboration with: Pelayo Salinas de León.

Since 2013, the Charles Darwin Research Station’s shark team, in collaboration with the Galapagos National Park Directorate, have conducted three annual trips to Darwin and Wolf to study sharks: one during the warm season, another during the cold season and another during the transition season. The aim of this study is to determine the impact of the El Niño / La Niña cycles and the effect of the total protection from fishing provided by the Marine Sanctuary established in 2016 on the main species of sharks and predatory fish.

Silky sharks and a Galapagos shark around the camera system of stereo-BRUVs.
Silky sharks and a Galapagos shark around the camera system of stereo-BRUVs. Photo by: Thomas Peschak / National Geographic.

Two underwater camera systems are used by our scientists:

  • Stereo-BRUVs (Baited Remote Underwater Video Surveys), which are remote cameras mounted on a triangular metal structure, to which a canister with bait is attached so that the odor attracts sharks.
  • Stereo-DOVs (Diver-Operated Video Surveys), which are also cameras don’t have a bait canister, and are carried by a scuba diving scientist.

Both methodologies consist of two cameras placed in the lower corners of a steel base with a distance of 70 cm between them, and at a converging angle of 6 cm. The cameras film in high definition and allow scientist to record different species of sharks and fish. Because they record in stereo (as in 3D), by using a specialized software called Event Measure, scientists can measure the length of animals very precisely. This is vital to understand the distribution of juvenile and adult sharks in the archipelago, as well as their diversity and relative abundance. The cameras are calibrated in a pool before each field trip to ensure their accuracy.

Deploying a stereo-BRUVs at Darwin Island.
Deploying a stereo-BRUVs at Darwin Island. Photo by: Pelayo Salinas de León / CDF.

There are two types of BRUVs: A bottom BRUVs that is placed at a depth of 25 meters (close to the seabed) and the mid-water BRUVs, which is placed in the middle of the water column, about 15 meters from the seabed. On one of the rope ends, a weight is attached to keep the cameras in position. A set of buoys are attached on top of the triangle that holds the cameras to keep it at the desired depth. An additional two buoys are attached to the other end of the rope on the surface, to be able to locate and recover the cameras after an hour and a half of filming.

Schematic representation of the differences between pelagic and benthic BRUVs.
Schematic representation of the differences between pelagic and benthic BRUVs. Infographic by: Daniel Unda / CDF.

Contrary to what most people think, sharks are usually very shy, and when scuba divers are in the water, many species simply do not come into sight. However, these species can be recorded by using remote cameras with bait and without divers. When the bait is in a closed container, sharks can smell but not eat, so their behavior is not altered. In a recent study published in the Marine Ecology Progress Series international journal by scientists from CDF, Massey University in New Zealand, and Curtin University in Australia, the results from 629 stereo-BRUVs conducted in the Galapagos Marine Reserve were presented. A total of 877 sharks were recorded from 10 different species, most prominently including hammerheads, black tip and Galapagos sharks. Some species that were frequently recorded by the BRUVs, such as the tiger shark or hound shark, are very rarely seen by scuba divers in the Galapagos. The data obtained in Galapagos will also contribute to the Global Fin Print project, which aims to conduct the first global shark census using BRUVs.

 The eight most common shark species in the BRUVs: a) Bignose shark, b) Silky shark, c) Galapagos shark, d) Black tip shark, e) Tiger shark, f) Scalloped hammerhead shark, g) White tip shark, h) Galapagos bullhead shark, i) White-margin fin smooth-houndshark, j) Spotted houndshark.
The eight most common shark species in the BRUVs: a) Bignose shark, b) Silky shark, c) Galapagos shark, d) Black tip shark, e) Tiger shark, f) Scalloped hammerhead shark, g) White tip shark, h) Galapagos bullhead shark, i) White-margin fin smooth-houndshark, j) Spotted houndshark. Figure from Acuña-Marrero et al. 2018.

On the other hand, when conducting surveys with DOVs, a scientist carries the stereo-camera system while scuba diving. Scientists film a linear transect following the depth contour of the seabed at a depth of 20 m. A second diver carries a surface GPS located on a plastic buoy to record a track of the area covered. Swimming at a constant speed, scientists cover an approximate distance of 500 meters.

Schematic representation of a survey using DOVs.
Schematic representation of a survey using DOVs. Infographic by: Daniel Unda / CDF.

After returning from the field, the GPS data is downloaded to quantify the distance covered and videos are analyzed using the Event Measure software. Using this software, recorded species can be identified, the total number of individuals are counted and their length is estimated precisely. Unlike the BRUVs, videos filmed with DOVs allow us to estimate and standardize the area covered in order to estimate sharks and fish biomass per unit area (kilograms per square meter), which is the standard global unit used for coastal species. In 2016, Charles Darwin Foundation and National Geographic Pristine Seas scientists used two years of DOVs data to determine that Darwin and Wolf islands have the largest global shark biomass

Scientist David Acuña, carrying out a DOVs transect at Wolf Island.
Scientist David Acuña, carrying out a DOVs transect at Wolf Island. Photo by: Pelayo Salinas de León / CDF.

The use of the stereo-video methodology requires much more time to obtain results, but compared to the traditional underwater visual censuses (UVC), that have a very high error rate, the percentage error in length measurements is less than 5%. This makes the BRUVs and DOVs methodologies not only complementary, but very efficient to study sharks and other fish in the archipelago.

This project is carried out in collaboration with the Galapagos National Park Directorate, Massey University in New Zealand and Curtin University in Australia. It is possible thanks to the support of Save Our Seas Foundation, Helmsley Charitable Trust, National Geographic Pristine Seas, and several other individual donors.

This is one of the Charles Darwin Foundation’s many projects in Galapagos and we depend entirely on the generosity of our supporters. Please donate today.

The “Charles Darwin Foundation for the Galapagos Islands”, in French “Fondation Charles Darwin pour les îles Galapagos”, Association International sans but lucratif (“AISBL”), has its registered office located at Drève du Pieuré 19, 1160 Brussels, and is registered under the trade registry of Brussels under the number 0409.359.103.

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