Images as proximity sensors: the incidence of conspecific foraging in Antarctic fur seals

Abstract

Background:Although there have been recent advances in the development of animal-attached 'proximity' tags to remotely record the interactions of multiple individuals, the efficacy of these devices depends on the instrumentation of sufficient animals that subsequently have spatial interactions. Among densely colonial mammals such as fur seals, this remains logistically difficult, and interactions between animals during foraging have not previously been recorded. Results:We collected data on conspecific interactions during diving at sea using still image and video cameras deployed on 23 Antarctic fur seals. Animals carried cameras for a total of 152 days, collecting a total of 38,098 images and 369 movies (total time 7.35 h). Other fur seals were detected in 74 % of deployments, with a maximum of five seals detected in a single image (n = 122 images, 28 videos). No predators other than conspecifics were detected. Detection was primarily limited by light conditions, since conspecifics were usually further from each other than the 1-m range illuminated by camera flash under low light levels. Other seals were recorded at a range of depths (average 27 ± 14.3 m, max 66 m). Linear mixed models suggested a relationship between conspecific observations per dive and the number of krill images recorded per dive. In terms of bouts of dives, other seals were recorded in five single dives (of 330) and 28 bouts of dives <2 min apart (of 187). Using light conditions as a proxy for detectability, other seals were more likely to be observed at the bottom of dives than during descent or ascent. Seals were also more likely to be closer to each other and oriented either perpendicular or opposing each other at the bottom of dives, and in the same or opposite direction to each other during ascent. Conclusions:These results are contrary to animal-attached camera observations of penguin foraging, suggesting differing group-foraging tactics for these marine predators. Group foraging could have consequences for models linking predator behaviour to prey field densities since this relationship may be affected by the presence of multiple predators at the same patch.

Key Questions in Marine Megafauna Movement Ecology

“…However, breakthroughs in both hardware and analysis tools show promise for elucidating social interactions [e.g. 30,31].…”

Inferring animal social networks and leadership: applications for passive monitoring arrays

“…[14,15]). The logistical constraints to data storage, retrieval and battery life of such systems in marine environments or the ability to deploy and collect sufficient numbers of proximity loggers to capture the social structure of wide-ranging animals remains prohibitive and hence the emergence of analytical inference methods that can help to fill this gap with no extra risk or cost associated [16]. …”

View From Below: Inferring Behavior and Physiology of Southern Ocean Marine Predators From Dive Telemetry

“…Evidence for foraging flexibility or prey switching may come from high variability and/or temporal (e.g., seasonal) changes in individual dive (Deagle et al, 2007) or bout (Harcourt et al, 2002) characteristics which can be difficult to detect. When animals are large enough, prey selection can be directly observed using miniature cameras mounted on a data logger, as has been done successfully on Antarctic fur seals (Hooker et al, 2002(Hooker et al, , 2015Heaslip and Hooker, 2008). Cameras were also deployed on gentoo and Adélie penguins foraging on krill and fishes schooling underneath sea ice (Takahashi et al, 2008;Watanabe and Takahashi, 2013).…”