Sharks shape the geometry of a selfish seal herd: experimental evidence from seal decoys

Vos, Alta De; O’Riain, M. Justin

doi:10.1098/rsbl.2009.0628

Cited by 47 publications

(35 citation statements)

References 16 publications

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“…It was assumed that this predatory breaching behaviour would provide a good opportunity to test the effect of the electric field. Experimental decoy tows have been successfully used to study Cape fur seal predation risk when moving near Seal Island [45].…”

Section: Methodsmentioning

confidence: 99%

“…A fibreglass coated foam seal decoy was towed 20–25 m behind a vessel at speeds of 8–10 km.hr –1 , which was based on travelling speeds of Cape fur seals leaving Seal Island [45]. To maximise the chance of eliciting a predatory response, the tow time and route were chosen based on the knowledge that predator-prey activity is spatio-temporally confined and predictable at Seal Island [43].…”

Section: Methodsmentioning

confidence: 99%

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Effects of an Electric Field on White Sharks: In Situ Testing of an Electric Deterrent

et al. 2013

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Elasmobranchs can detect minute electromagnetic fields, <1 nVcm–1, using their ampullae of Lorenzini. Behavioural responses to electric fields have been investigated in various species, sometimes with the aim to develop shark deterrents to improve human safety. The present study tested the effects of the Shark Shield Freedom7™ electric deterrent on (1) the behaviour of 18 white sharks (Carcharodon carcharias) near a static bait, and (2) the rates of attacks on a towed seal decoy. In the first experiment, 116 trials using a static bait were performed at the Neptune Islands, South Australia. The proportion of baits taken during static bait trials was not affected by the electric field. The electric field, however, increased the time it took them to consume the bait, the number of interactions per approach, and decreased the proportion of interactions within two metres of the field source. The effect of the electric field was not uniform across all sharks. In the second experiment, 189 tows using a seal decoy were conducted near Seal Island, South Africa. No breaches and only two surface interactions were observed during the tows when the electric field was activated, compared with 16 breaches and 27 surface interactions without the electric field. The present study suggests that the behavioural response of white sharks and the level of risk reduction resulting from the electric field is contextually specific, and depends on the motivational state of sharks.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Effects of an Electric Field on White Sharks: In Situ Testing of an Electric Deterrent

et al. 2013

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“…Antipredator tactics of seals have been explored (Laroche et al . ; De Vos and O'Riain , ) but have largely excluded sublethal impacts of such predation on spatiotemporal movement patterns and both social and thermoregulatory behaviors in different predation risk scenarios.…”

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confidence: 99%

Behavior of Cape fur seals (Arctocephalus pusillus pusillus) in response to spatial variation in white shark (Carcharodon carcharias) predation risk

Vos

O’Riain

Meÿer³

et al. 2015

Marine Mammal Science

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Foraging and predation risk are often separated at rookeries of marine central place foragers, thus offering an opportunity to gain insight into how predator‐avoidance shapes the behavior of prey. Here we compare the behavior of Cape fur seals (Arctocephalus pusillus pusillus) at two island rookeries with and without white shark (Carcharodon carcharias) predations, and assess seal behavior in relation to marked spatiotemporal variation in risk at the high‐risk site (Seal Island, South Africa). Our results show that seal behavior at the two sites is comparatively similar in summer, when predation risk is low at both sites, but not in winter. Compared to seals at the “low‐risk” site, seals at Seal Island avoided deep‐water habitat around the island at high risk times and restricted their use of this habitat in favor of safe, shallow waters when engaging in social and thermoregulatory behaviors. Seals increased their frequency of jostling, porpoising, and diving when moving through the danger zone and seals in groups were safer than single individuals. Overall, our results suggest that seal behavior around the high‐risk site is strongly affected by predation risk, and show this rookery to be an excellent predator‐prey system at which to evaluate long‐standing ecological hypotheses.

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“…The selfish herd effect (Hamilton, ) occurs when members of a group attempt to use each other as cover from predators (Beauchamp, ; Caro, ). This effect can also drive sociality and spacing patterns in animals (De Vos & O’Riain, ). The confusion effect is another major benefit of sociality and is based on the idea that a predator has difficulty targeting an individual animal among the many possible targets in a fleeing group.…”

Section: Introductionmentioning

confidence: 99%

Is social coordination during escape flights a general phenomenon in birds?

Lima

Lee

2019

Ethology

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Escape from predatory attack as a socially coordinated group is observed in many social animals, including birds, especially those in more open habitats where the group itself may be the only source of protection from an attacking predator. For many social birds, however, woody vegetative cover is the main refuge from attack, but such birds might nevertheless benefit from social coordination during escape flights to cover. Such benefits could reflect the confusion effect, selfish herd effect, or the simple dilution of risk. We examined this possibility of coordinated escape in mixed flocks of wintering passerellid sparrows (Passerellidae). These free‐living birds fed in a patch of food flanked on opposite sides by two refuges composed of woody cover. Under such conditions, coordination in escape behavior should be expressed as a tendency to escape together as a group to the same cover location. Such behavior, however, was not the rule. During spontaneous flushes to cover, a group of escaping birds stayed together only when one cover location was clearly closer than the other. With cover equidistant from the food patch, escaping flocks tended to split about evenly between cover locations. Birds in close proximity prior to an escape flight did not show enhanced escape coordination, nor did those feeding at significant distances from protective cover. Evidence of escape coordination was observed in small groups (two–four birds), but even in such groups, flock splitting during escape was generally the rule. Flock splitting during attacks might reflect some sort of strategic decision‐making process that lessens the risk of capture, but the most parsimonious explanation is that (all else equal) birds head for the nearest refuge, largely irrespective of the behavior of their flockmates. Our results thus provide little evidence of flock‐wide social coordination during escape flights in cover‐dependent birds.

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Sharks shape the geometry of a selfish seal herd: experimental evidence from seal decoys

Cited by 47 publications

References 16 publications

Effects of an Electric Field on White Sharks: In Situ Testing of an Electric Deterrent

Effects of an Electric Field on White Sharks: In Situ Testing of an Electric Deterrent

Behavior of Cape fur seals (Arctocephalus pusillus pusillus) in response to spatial variation in white shark (Carcharodon carcharias) predation risk

Is social coordination during escape flights a general phenomenon in birds?

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