Movement patterns of giant Pacific octopuses, Enteroctopus dofleini (Wülker, 1910)

Abstract

We attached sonic transmitters to, and tracked, 40 giant Pacific octopuses (Enteroctopus dofleini) ranging from <1 to 21kg in size in south-central Alaska using near-continuous tracking by fixed-array receivers and intermittent tracking with a mobile receiver. We documented area use, daily activity patterns, spatial scale of movements and whether these differed by octopus size, and whether octopuses actively selected habitats. Near-continuous fixed tracking provided positions about every 4 min over a limited area, while intermittent mobile tracking provided positions every 1–6h but over open and larger areas. Mantle-mounted transmitters on modified Peterson disks had >83% retention to the end of a tracking period (range <1day [before animal left the study area] to at least 88days post-release), an improvement over published studies. Octopuses were found to be stationary or hiding 94% of the time. Otherwise, octopuses were active throughout the day but more so from midnight to 0500. During low tides, movements were restricted for animals in intertidal habitats but not for those deeper. Maximum movement distance from release was 4.8km (by a 16.5kg female). Minimum convex polygon area use averaged 4,300m2 for the smallest animals to an average over 50,000m2 for the largest during 2 to 20days of tracking, substantially larger than previously reported. Larger octopuses moved further and used greater area than smaller animals, but differences between sexes were not significant.Stationary behavior and periods without detection (rest) by fixed near-continuous tracking were bi-modally distributed, with peaks <3h duration and >18–48h. Direct movements (indicating relocation or den switching) were common at night, central-tendency movements (indicating localized area use and return to den) were common at dawn, and stationary behavior was common in daylight, although each pattern occurred at all periods. Central-tendency movements recorded by intermittent tracking were oriented parallel to contours, while movements without central-tendency crossed contours, suggesting that animals navigate by contour following to return to a known den. During a relocation experiment, octopuses released at shallow depths moved deeper and those released deeper moved shallower, both into habitats with greater kelp cover. Although >90% of their time was spent stationary and hiding, Enteroctopus dofleini utilizes information about its environment (contour following), selects habitats (preference for more kelp cover), and occupies large use areas (minimum convex polygons) by making substantial direct movements from previous use areas.