Obituary: Adrianus Kalmijn, UCSD biologist who revealed sharks’ ‘sixth sense’ of hunting, dies at 88

Adrianus J. Kalmijn,the UC San Diego biophysicist who discovered that sharks and skates can detect the weak electric field produced by other fish, giving them a tremendous advantage in hunting prey, died on Dec. 7 at Scripps Green Hospital in La Jolla. He was 88.

Kalmijn, a longtime Encinitas resident, passed away of acute myeloid leukemia, according to his son, Jelger Kalmijn, a UC San Francisco researcher who often worked on his father’s projects.

The defining discovery of his life came in 1971, when the elder Kalmijn was a young scientist at UC San Diego’s Scripps Institution of Oceanography.

It was widely known that sharks have many ways of sensing what’s around them, especially through their sense of smell. Tiny droplets of blood can be picked up far, far away.

But Kalmijn and his collaborators took things further, showing experimentally that the tiny pores in the snout of sharks and skates served as electro-receptors that pick up on the electric signals of other fish, even if the fish are hidden beneath the sand or in close relation to food, such as chum.

This dazzled scientists, who said that Kalmijn had discovered that sharks have a “sixth sense,” one that also helps them in navigation. The finding added to the somewhat mystical reputation of sharks.

“His contribution to shark sensory biology is not just significant, it is monumental,” Kyle Newton, a Washington University of St. Louis researcher, said in a statement.

“He basically discovered that the ampullae of Lorenzini (or pores in the snout) are the organ responsible for electro-reception and he noted that this is a major tool for hunting prey that hide buried in the sediment.”

Kalmijn’s death brings an end to a roughly 60-year science career that includes papers he was working on just two days before he died.

He was born on Nov. 7, 1933, in Utrecht, the Netherlands. His father, Joseph, was a high school math teacher. His mother, Johanna Kalmijn-Spierenburg, wrote children’s books.

After attending high school, Adrianus Kalmijn served in the military for about three years, where he learned a great deal about radar and signals. That experience helped him take a practical, applied approach to his work when he studied at Utrecht University.

He later served on the university’s faculty and did extensive shark research at the Woods Hole Oceanographic Institution in Woods Hole, Mass., before he settled in for the long term at Scripps Oceanography in the early 1980s.

With support from the Navy and the Keck Foundation, he built a major electromagnetic research facility that was in use for decades. Kalmijn’s findings greatly expanded science’s understanding of how sharks hear, as well as how their other senses work.

“My father felt a deep humility toward animals,” Jelger Kalmijn said. “He felt that they had so much to teach us about the world.

“He would always spend Christmas morning with us, but by the afternoon, he was back in his office, working. That’s what he loved to do. He was obsessed.”

UCSD said that Kalmijn is survived by is wife, Vera, of Encinitas; son Jelger Kalmijn of Encinitas, daughter Thera Kalmijn of Berkeley; son Sander Kalmijn of Drymen, Scotland, and six grandchildren.

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