Den-Associated Behavior of Octopus rubescens Revealed by a Motion-Activated Camera Trap System

Dens are a crucial component of the life history of most shallow water octopuses. However, den usage dynamics have only been explored in a few species over relatively short durations, and Octopus rubescens denning behavior has never been explored in situ. We built four underwater camera traps to observe the behavior of O. rubescens in and around their dens. To distinguish individuals, octopuses were captured and given a unique identifiable visible implant elastomer tag on the dorsal side of their mantle. After being tagged and photographed, each octopus was released back to its original capture site within its original den bottle. The site is unique in that octopuses reside almost exclusively in discarded bottles, therefore aiding in locating and monitoring dens. Motion-activated cameras were suspended in a metal field-of-view above bottle dens of released octopuses to observe den-associated behaviors. Cameras were regularly retrieved and replaced to allow continuous monitoring of den locations in 71 h intervals for over a month. We found that O. rubescenswas primarily active during the day and had frequent interactions with conspecifics (other members within the species). We also found that rockfish and red rock crabs tended to frequent den locations more often when octopuses were not present, while kelp greenling both visited dens more frequently and stayed longer when octopuses were present. Our results, demonstrate the utility of motion-activated camera traps for behavioral and ecological studies of nearshore mobile organisms.