An underwater canyon that traps krill: the secret of the whales in the Humboldt Archipelago

June 30, 2024

Featured image © Francis Pérez

Ocean Story contributed by Susannah Buchan, Humboldt Archipelago Hope Spot Champion

They say in Caleta Chañaral de Aceituno, located on the southern limit of the Atacama Region, that in the last five years the presence of whales has increased around Chañaral Island. Fin, blue and humpback whales are the species that are most frequently sighted in the surroundings of this town, which is part of the Humboldt Archipelago Multiple Use Protected Coastal Marine Area, the first bi-regional initiative promoted in Chile, and which will debut as a protected area in 2023.

These immense animals – the blue whale and the fin whale are the two largest species on the planet – and consume several tons of krill a day during the spring, summer and autumn seasons in the Humboldt Archipelago, a unique natural laboratory for scientists who study large cetaceans.

A recent study shed new light as to why whales come to feed in this area. A team led by oceanographer Susannah Buchan and made up of researchers from the Center for Advanced Studies in Arid Zones (Ceaza), the Oceanographic Center of the Southeastern Pacific (Copas Coastal) and the Universidad Católica del Norte, Concepción, Valparaíso and Austral of Chile investigated the topic using – for the first time in Chile – a hydroacoustic instrument called the Zooplankton and Fish Acoustic Profiler (AZFP), which uses four simultaneous sound signals of different frequencies to detect different marine organisms. The researchers carried out  high-resolution surveys of krill in the water column and the seabed, in order to investigate its spatial distribution and the oceanographic conditions in which it develops.

The surveys yielded an important discovery: the presence of a steep underwater canyon to the south of Chañaral Island starting at a depth of 500m and quickly rising to 130m, acting like a funnel between the island and the continent. The researchers discovered that this canyon has the effect of channeling the nutrient-rich waters of the coastal upwelling that occurs outside the island into the interior of the channel. This explains the higher concentration of krill in the underwater canyon and channel. On the other hand, the local currents that are formed as a result of the presence of the canyon traps the biological productivity within the area.

The local community and tour operators in the area have already known for a long time that there is a greater number of whales feeding south of Chañaral Island and in the channel, which is locally named the ‘alley’.  Oceanographer Susannah Buchan, said that this highlights how important the transfer of local knowledge between the communities and researching scientists can be.

Carlos Olavarría, co-author of the study and director of Ceaza, points out that the conclusions of this research provide greater evidence of the importance of the Humboldt Archipelago for the development of scientific research. “The more in depth study of this area adds value to the productive initiatives of local inhabitants who carry out tourism and where the local knowledge transferred to its visitors sets it apart from other locations”.

The Underwater Canyons

Marcel Ramos, physical oceanographer at UCN and co-author of the study, explains that underwater canyons are important areas for biological productivity, because they “interrupt” coastal currents, generating cross-shore flows and gyres that affect the distribution of planktonic organisms. He adds that these gorges can transport nutrient-rich waters to the surface layer, where the sunlight reaches and therefore photosynthesis occurs, helping local fertilization of the coastal ocean. “The interesting thing about this study was the ability to resolve the distribution of krill with a spatial resolution of hundreds of meters,” explains Marcel Ramos. “This allows us to associate its spatial distribution with finer-scale topographic features and different oceanographic conditions during the observed summers, providing evidence on the importance of the island and the small underwater canyon for biological productivity in the area,” he adds.

For the Conaf park ranger and co-author of the study, Marinella Maldonado, the scientific culture and environmental care that the tourism workers of Caleta Chañaral de Aceituno have, has been growing over the years and “this research allows us to put much more value on the environment.” of the Chañaral Island Marine Reserve, the island and to the Humboldt Archipelago as a global ecosystem. As Conaf we are committed to environmental education and to always remain active with the community that works at sea, so that together we can continue strengthening the care of the reserves.”

Maldonado explains that those who work in the Chañaral Island sector of the Humboldt Archipelago have been keeping a collective record of sighting data since 2014. This information has been compiled by Conaf and contributes to the science being carried out in the area. In this investigation. “A group of boating service providers are currently using SMART, a data tool that collects, measures and evaluates data to improve the effectiveness of their wildlife conservation efforts. With all these important records, we hope to support this research and understand the oceanographic dynamics of the feeding area of ​​the baleen whales of Chañaral Island and expand protection of the habitat.”

Until a few months ago, only one nautical mile around Chañaral Island had effective protection, under the category of Chañaral Island Marine Reserve, this does not include the underwater canyon. In 2023, this changed with the creation of the “Humboldt Archipelago” Multi-Use Coastal Marine Protected Area, which will be managed by the Ministry of the Environment. What comes next is the development of a broad and participatory management plan, where scientific information will become relevant for decision-making. “Now we know that there is this physical characteristic that is of special importance in the whales’ habitat and this evidence gives us a greater basis to propose special conservation measures for this area, such as, for example, the restriction of boats and transit speeds, which increases the risk of a vessel striking and killing a whale. Collisions with boats are strongly affecting the fin whale, the predominant species in northern Chile,” says Buchan.

Luis Bedriñana, marine biologist at the UACh and co-author of the study, explains that the fin whale is the most common species of cetacean in the Humboldt Current. “We know that a part of the fin whale population remains in these waters all year round. The intense use that this whale gives to coastal areas makes it susceptible to interacting with human activities, such as maritime traffic, this increases the risk of collisions which can be lethal, as well as entanglement in fishing gear,” he says. This is why, Bedriñana continues, it is necessary to implement mitigation measures in the areas that have been identified as priorities by scientific studies.

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About Hope Spot Champion Susannah Buchan