Squid, octopus, and cuttlefish populations are booming across the world. These fast-growing, adaptable creatures are perfectly equipped to exploit the gaps left by extreme climate changes and overfishing, according to a study colleagues and I published in the journal Current Biology.

Humans have reached and in many cases surpassed sustainable fishing limits, as our growing population demands more food. In terms of the food web, we tend to start from the top and fish “downwards.” Fishermen fish out the top predators first, including large sharks, tuna, and whales, and then medium size fish such as cod, hake, and halibut that usually live long and grow slowly.

The vacant space left by fish may be occupied by other species, with rapidly proliferating animals having a clear advantage. And these animals are cephalopods. Squid, octopus, and cuttlefish live in the “fast lane”, growing quickly and typically living for only one or two years. They produce lots of eggs, and their eggs have relatively low mortality rates, whether thanks to patient brooding by an octopus mother or the protective mucous that covers embryonic squid. These traits enable cephalopods to adapt rapidly to changes in the environment which have become even more pronounced in recent decades thanks to human activity.

Counting cephalopods

These are elusive creatures, notoriously difficult to count. To get a better estimate of their overall abundance, we looked at what we call catch rates—how many were caught per vessel per unit of time—over the past six decades. We used an extensive dataset of 35 different species (52 percent squid, 31 percent octopus, and 17 percent cuttlefish) from all major oceanic regions. Most were “target” species deliberately sought by fishermen, others were non-target or bycatch species. We used data from both regular commercial fisheries and specific research surveys.

Everywhere we looked we found a substantial and statistically significant increase. Bottom-dwelling octopus and cuttlefish who live relatively static lives are thriving, as are squid that hover over the bottom, along with those in the open ocean that may travel thousands of kilometres from spawning to feeding sites. At a time when life in the oceans is threatened, cephalopods seem able to buck the trend.