Science Program⎢Cape Verde⎢2021

Studying the common octopus
of Cabo Verde

Partnering with Faculdade de Ciências da Universidade de Lisboa

Arriving in Cape Verde, Charles Darwin’s fascination with the common octopus, Octopus vulgaris, grew quickly. However, he faced limitations due to the technological constraints of his time. Wondering about the potential discoveries Darwin could have made with modern diving suits, our team launched an underwater scientific program from our ship. Biologist Eduardo Sampaio, specializing in cephalopod behavior in the Lisbon Faculty of Science, joined us for 60 hours of underwater research over 15 days.

Our objectives were twofold: firstly, to gain a better understanding of octopus presence on the desert islands of Cape Verde, and secondly, to conduct behavioral tests on them.

Days of Exploration

Associated Researcher

Hours Underwater

Scientific Conclusions

1832

I was much interested, on several occasions, by watching the habits of an Octopus, or cuttle-fish. Although common in the pools of water left by the retiring tide, these animals were not easily caught. By means of their long arms and suckers, they could drag their bodies into very narrow crevices; and when thus fixed, it required great force to remove them.

While looking for marine animals, with my head about two feet above the rocky shore, I was more than once saluted by a jet of water, accompanied by a slight grating noise.

– Charles Darwin, Voyage of the Beagle, 1832

2021

With the aid of scuba diving suits, we have now scientifically confirmed the presence of Octopus vulgaris in locations previously inaccessible to Charles Darwin.

Although the common octopus population in Cape Verde is believed to have remained relatively stable over 200 years, this conclusion relies more on general reasoning than on precise data.

The species is subject to small-scale fishing by local fishermen. Simultaneously, industrial fishing carried out by Spanish and Chinese boats focuses on large fish and sharks, which happen to be natural predators of octopuses. This dual dynamic is resulting in a balanced and stable population for the species.

1832

I was much interested, on several occasions, by watching the habits of an Octopus, or cuttle-fish. Although common in the pools of water left by the retiring tide, these animals were not easily caught. By means of their long arms and suckers, they could drag their bodies into very narrow crevices; and when thus fixed, it required great force to remove them.

While looking for marine animals, with my head about two feet above the rocky shore, I was more than once saluted by a jet of water, accompanied by a slight grating noise.

– Charles Darwin, Voyage of the Beagle, 1832

2021

With the aid of scuba diving suits, we have now scientifically confirmed the presence of Octopus vulgaris in locations previously inaccessible to Charles Darwin.

Although the common octopus population in Cape Verde is believed to have remained relatively stable over 200 years, this conclusion relies more on general reasoning than on precise data.

The species is subject to small-scale fishing by local fishermen. Simultaneously, industrial fishing carried out by Spanish and Chinese boats focuses on large fish and sharks, which happen to be natural predators of octopuses. This dual dynamic is resulting in a balanced and stable population for the species.

Eduardo’s testimony

Hi, I’m Eduardo. I’m 33, studied Biology at the University of Lisbon, and developed a soft spot for octopuses during my studies. I am also a visiting scientist at the Max Planck Institute of Animal Behavior in Germany, and will continue my studies there as a postdoc in the Department of Collective Behaviour. My research focuses on the behavior of cephalopods, in particular I have studied how decision-making in these invertebrates is shaped by social contexts. Regarding octopuses, I’m interested in understanding more about how they coordinate with fish while hunting. So when Victor reached out and invited me to be part of the Captain Darwin expedition, I immediately accepted. It was an incredible opportunity to learn more about the natural history of octopuses, and to verify if collective octopus-fish hunts occurred in temperate ecosystems, which could help me define fieldwork locations for my next trips.

The Captain Darwin near the island of Razo, one of the three desert islands with Santa Luzia and Branco.

Diving from the ship, which carries two 14-litre twin tanks and a thermal compressor.

Eduardo Sampaio is a cephalopod biologist at the Lisbon Faculty of Sciences.

Although we weren’t in an exact replica of the vehicle, the fact that we didn’t have Internet, most of the electronics were conditioned to the available electricity we had, and the typical social interactions of being on a boat, really made me feel like Charles Darwin a little bit. On the boat, I took the opportunity to read his “The Origin of Species”. Despite knowing the fundamentals of Darwin’s theory of evolution by natural selection, I had never read the book itself. On a daily basis, we would wake up around 7 in the morning, eat something and drink hot coffee while watching the sunrise – with the desert islands on the background. During this time, we would plan the rest of the day: where to dive, how many dives during the day, lunch hour, sometimes a bit of own time after lunch (very useful for naps), and the rest of the day to go through video material and the occasional beer at sunset.

The waters of Cape Verde offer good visibility, and a mild temperature of around 27°C.

At 30 meters depth, Eduardo has just observed, under a rock, the first octopus of the mission.

Octopuses, in the middle of the breeding season, stay hidden in their den and avoid contact with divers.

When our diving program started, we were surprised. We found octopuses, but they weren’t hunting outside of their dens. It was mating season. We recorded some of the couples we found in Raso and Santa Luzia, but we wanted to get more from this expedition. To that end, we changed our approach from “finding and following” to “surveillance” methods: when we found an octopus or a couple, we would install several stationary cameras that could film their behavior in our absence. Moreover, I had thought about testing some cognitive puzzles or methods in the wild, so on my luggage I included some simple objects that could aid in experiments, among which was a mirror. We then used that mirror and stationary cameras to perform simple mirror tests, which assess how animals react to their own reflection. These tests are used to measure aggression, and can also be used as first stages for self-recognition tests in the lab, to assess if individuals are able to recognize themselves in the mirror. This preliminary exploration determined that octopuses do react to mirrors, which makes them suitable candidates for self-recognition tests. Thus, our exploration in Cabo Verde resulted in: octopus mating reports, a potential sighting of a new invasive species (yet to be confirmed), preliminary validation of the mirror test, and, last but by no means least, an amazing personal experience for which I’m incredible thankful to Nico, Martin, and Victor.

The dives continue even at night, a period conducive to octopus activity.

An octopus reacts strongly to the mirror test, conducted for the first time in Cape Verde in the wild.

Eduardo and Nicolas, the mission’s diving director, analyze the images captured underwater.

Scientific Conclusions

Our vessel proved ideal for conducting remote underwater scientific programs, equipped with autonomous capabilities and aquatic exploration tools, operated by a skilled team of divers, sailors, and scientists. The intensive work yielded three significant scientific findings, and led to an article published in the esteemed American magazine Science.

Presence of Octopus vulgaris in the Subtidal Zone • Previous observations by Eduardo, conducted from the surface using snorkeling, could not confirm the presence of the common octopus beyond the intertidal zone. However, with the scuba diving equipment provided by Captain Darwin, Eduardo was able to scientifically establish the presence of Octopus vulgaris up to 30 meters deep in Cape Verde.

Lag in the Reproduction Period • Among the six observed individuals, all were in reproductive phases, and they even managed to film a reproduction event using a strategically placed camera near a female octopus’s den. Interestingly, the observed reproductive cycle in November differed from the species’ known schedule in the North Atlantic, which typically occurs a month earlier. Further research is necessary to unravel the reasons behind this discrepancy.

Reactions to the Consciousness Test in the Wild • Eduardo conducted the “mirror” consciousness test on Octopus vulgaris in their natural habitat in Cape Verde, a first of its kind experiment. The recorded reactions were strong, but the test’s scientific method did not conclusively establish the species’ consciousness. Nonetheless, these experiments lay the groundwork for further laboratory testing, providing valuable insights into the cognitive abilities of these fascinating creatures.

How are Octopus doing, 200 years after Darwin?

Currently, the region faces anthropogenic pressure due to fishing activities. Despite being a nature reserve, some fishermen from neighboring islands come here to fish octopus for use as bait, potentially reducing the population of Octopus vulgaris.

Simultaneously, there is a concerning deficit of large predators, such as sharks, primarily because they are also being heavily fished (by industrial fishing companies), even more so than octopuses. Unfortunately, obtaining precise data is challenging, as some of it pertains to illegal fishing, making it difficult to accurately assess the situation.

On the whole, considering the decline in natural predators and the fishing threat, the population appears to have remained relatively stable since Darwin’s time. Unlike overexploited areas like Israel, for instance, octopuses here continue to display wariness, indicating the continued presence of their predators. However, sharks and large fish have experienced a significant decline in their populations since the 19th century.

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