Searching for prey in a three-dimensional environment: hierarchical movements enhance foraging success in northern elephant seals

Open Access Peer Reviewed Publication 2016

Functional Ecology

1. Foraging theory predicts that predators adjust their movements according to the spatial distribution of prey. Since prey is often patchily distributed, area-restricted search (ARS) behaviour, characterized by sinuous search paths of predators with increased turning frequency, should be effective in foraging. 2. However, it remains unclear whether ARS behaviour actually enhances foraging success in free-ranging animals, especially in marine animals that forage in a three-dimensional (3D) environment. 3. Here, we reconstructed 3D dive paths of a highly pelagic marine predator, the northern elephant seal (n = 3), with multisensor data loggers that recorded depth, tri-axis acceleration, tri-axis magnetism and swim speed. We identified spatial scales of volume-restricted search (VRS, termed for 3D ARS) behaviour using spherical first-passage time analysis on 3D dive paths, accompanied with quantifying feeding rates in VRS by using mandible accelerometers that recorded feeding events. 4. Seals exhibited VRS behaviour at two spatial scales (radius of spheres): small-VRS (8–10 m) and large-VRS (17–19 m). Most feeding events occurred in VRS zones (78 and 86% for small and large-VRS, respectively), although VRS accounted for a small proportion of bottom phase of dives in distance travelled. This suggests a strong link between VRS behaviour and foraging success. 5. There was a hierarchical structure to the VRS; most small-VRS (95%) were nested within large-VRS (i.e. nested VRS). Importantly, nested VRS had significantly higher feeding rates than non-nested VRS, because nested VRS contained small- and large-VRS with higher and lower feeding rates, respectively. These results suggest that seals forage on mesopelagic prey in a hierarchical patch system where high-density patches at small scales are nested within low-density patches at larger scales. 6. We demonstrated that seals employed scale?dependent, hierarchical 3D movements and that underwater fine?scale sinuous movements (i.e. VRS) were strongly linked to higher foraging success, particularly within nested VRS zones. We suggest that seals enhanced foraging success by employing hierarchical movements that possibly reflect the hierarchical property of prey distribution. Although recent studies advocate that optimal searching behaviour would be scale?independent (e.g. Lévy walk), our study suggests that scale?dependent processes are important components of successful foraging behaviour.

Link To Publication

Similar Research

Anthropogenic sound and marine mammal health: measures of the nervous and immune systems before and after intense sound exposure

Pay-walled Journal Article 2004

Canadian Journal of Fisheries and Aquatic Sciences

Anthropogenic sound is a potential stressor for marine mammals that may affect health, as has been demonstrated in other mammals. Therefore, we have initiated investigations on...
Read More

International Regulation Of Transboundary Pollutants: The Emerging Challenge Of Ocean Noise

Open Access Journal Article 2001

Ocena and Coastal Law Journal

Transboundary pollution law poses the challenge of addressing environmental problems irrespective of boundaries in an international legal system that values, above all, territorial sovereignty of individual...
Read More

A Brief Review of Anthropogenic Sound in the Oceans

Open Access Journal Article 2007

International Journal of Comparative Psychology

Sound in the oceans is generated by a variety of natural sources, such as breaking waves, rain, and marine animals, as well as a variety of...
Read More

Effect of anthropogenic low-frequency noise on the foraging ecology of Balaenoptera whales

Pay-walled Journal Article 2006

Animal Conservation

The human contribution to ambient noise in the ocean has increased over the past 50 years, and is dominated by low-frequency (LF) sound (frequencies <1000 Hz)...
Read More

Response and Responsibility: Regulating Noise Pollution in the Marine Environment

Pay-walled Journal Article 2007

Journal of International Wildlife Law and Policy

The ocean is becoming an increasingly noisy environment. With a rise in com-mercial shipping, resource extraction activities, and military-related activities,the underwater ocean environment is a virtual...
Read More

Influences of man-made noise and other human actions on cetacean behaviour

Pay-walled Journal Article 1995

Marine and Freshwater Behaviour and Physiology

Behavioral reactions of cetaceans to man-made noises are highly variable, ranging from attraction (e.g. bow riding by dolphins) or no response through short-term changes in behaviour...
Read More

Determination of environmental sensitivity of acoustic propagation on continental shelves using an equivalent fluid parabolic equation model

Pay-walled Journal Article 1995

The Journal of the Acoustical Society of America

A coupled environment and acoustic prediction system was developed to evaluate the sensitivity of acoustic propagation on the continental shelf to water column and sediment properties....
Read More

Effects of underwater noise on auditory sensitivity of a cyprinid fish

Pay-walled Journal Article 2001

Hearing Research

The ability of a fish to interpret acoustic information in its environment is crucial for its survival. Thus, it is important to understand how underwater noise...
Read More

Effects of noise exposure on click detection and the temporal resolution ability of the goldfish auditory system

Pay-walled Journal Article 2005

Hearing Research

Hearing specialist fishes investigated so far revealed excellent temporal resolution abilities, enabling them to accurately process temporal patterns of sounds. Because noise is a growing environmental...
Read More

The effects of noise on the auditory sensitivity of the bluegill sunfish, Lepomis macrochirus

Pay-walled Journal Article 2002

Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology

As concerns about the effects of underwater anthropogenic noises on the auditory function of organisms increases, it is imperative to assess if all organisms are equally...
Read More