The squids are all right — as are their cephalopod cousins the cuttlefish and octopus.

In the same waters where fish have faced serious declines, the tentacled trio is thriving, according to a study published Monday.

“Cephalopods have increased in the world’s oceans over the last six decades,” Zoë Doubleday, a marine ecologist from the University of Adelaide in Australia, and lead author of the study, said in an email. “Our results suggest that something is going on in the marine environment on a large scale, which is advantageous to cephalopods.”

Dr. Doubleday and her team compiled the first global-scale database of cephalopod population numbers, spanning from 1953 to 2013. It included historical catch rates for 35 cephalopod species, including the Japanese flying squid, the giant Pacific octopus and the common cuttlefish. The species inhabit marine ecosystems all over the world, from Australia and the United States to Morocco and Madagascar, among other countries.