Munk Foundation supports expeditions to study mysterious devil rays

While most rays are solitary or travel in small schools, Munk’s devil rays will form "super schools."
While most rays are solitary or travel in small schools, Munk’s devil rays will form “super schools” of hundreds of thousands.
(Paula Selby)

Even in death, famed La Jolla oceanographer Walter Munk is furthering science that aims to solve the mysteries of the deep.

To continue Munk’s legacy of “daring exploration and discovery through scientific research, education and ocean conservation,” the Walter Munk Foundation for the Oceans is supporting expeditions to Baja California, Mexico, to study the devil rays that bear Munk’s name.

Munk, a La Jolla resident known as the “Einstein of the Oceans” for his research at UC San Diego’s Scripps Institution of Oceanography, died in 2019 at age 101.

On the most recent trip in May, a team of marine scientists, Ph.D. and master’s degree candidates and foundation members embarked on a 10-day expedition to study the ecology and conservation of a species of pygmy devil ray known as mobula munkiana that lives in the Gulf of California off La Ventana in Baja California Sur.

“The species has been understudied aside from being described, and in the last few years there has been more attention to them,” said team member Josh Stewart, who completed his Ph.D. at Scripps Oceanography with a focus on manta and devil rays. “They are unique among their relatives. Most rays are more solitary or travel in smaller schools, but Munk’s ray forms super aggregations that have hundreds of thousands of individuals. At certain times of year and in some locations, they form these super schools. You see videos of people who have flown over them in a plane and it just keeps going. We don’t know why they form these groups.”

The trips, which began last year, aim to answer that question.

“Any time a species aggregates like that, it makes them vulnerable to impacts such as fishing or hunting,” Stewart said. “Any time you get a huge population in one place at one time, if something happens during that event, it can be catastrophic for that species. The data we collect helps us understand the ‘why,’ which is one of the hardest questions to answer.”

The running theory is that the rays gather in such large schools to reproduce, which Stewart said the team will continue to study and return to the area next year to further evaluate.

The first expedition last year was “kind of a dud,” Stewart said. Weather changed the water conditions so the team couldn’t see the rays.

Team members on an expedition supported by the Walter Munk Foundation for the Oceans tag a mobula munkiana for further study.
Team members on an expedition supported by the Walter Munk Foundation for the Oceans tag a mobula munkiana, or Munk’s devil ray, for further study.
(Mads St. Claire)

In the May attempt, local fishermen in Baja helped catch and tag the rays so the team can see where they go after they assemble.

Leading the team was Marta Diaz Palacious, a Ph.D. candidate at Centro Interdisciplinario de Ciencias Marinas in Mexico. She started studying the Munk rays six years ago in the wake of increased eco-tourism that drew attention to them.

“My focus is to study the species, the ecology and the abnormality of the Munk rays to understand possible management measures,” she said.

Noting that it is legal to fish for rays in other parts of the world, Palacious said she feels her work “gives me hope” that if certain protective measures are put in place, it can help species in need.

The International Union for Conservation of Nature rates the status of the Munk’s devil ray as “vulnerable,” largely because it is frequently caught in fishing nets.

“These animals’ populations were not as abundant as they are now,” Palacious said. “Seeing the aggregations gives me hope that if you protect something, the power of nature will let them recover. Munk rays are given protection and they can recover.”

Marta Diaz Palacious releases a tagged Munk ray back into the ocean.
(Mary Coakley Munk)

Italian ecologist Giuseppe Notarbartolo di Sciara, who discovered the species in 1983 and named it, was also on hand in Baja.

“Having the blissful opportunity of being in the water surrounded by a multitude of happy munkianas swimming around me was something quite different, as you imagine,” di Sciara said. “That experience provided me with a sense of accomplishment for having introduced the species to science through my formal description, because I realized that by describing it I have managed, perhaps unwittingly, to also diffuse its extraordinary beauty and natural value.”

Mary Coakley Munk, Walter’s widow and president of the Walter Munk Foundation for the Oceans, said: “It is incredible to facilitate work like this. ... This, I would say, meets the [foundation’s] mission from the standpoint that it is exploration and constantly discovering something about the mobula and the conditions of the Sea of Cortez.

“They are a vulnerable species, and we are learning so much about them. All of it is related to ocean conservation.”

She also commended the scientists involved in the work. “Just to see the dedication and passion that these young students have for the work they’re doing … was amazing,” she said. “Walter would have been proud to see the work going on in his name. It’s really inspiring to see what the young scientists are doing and how much they care.” ◆