Studying Killer Whale Predation in the Field A Sound Approach to Detecting Kills

Volker B. DEECKE

John K.B. FORD

Peter J.B. SLATER

•Delineating the ecological role of mammal-eating killer whales requires precise knowledge about their abundance, dietary preferences, and the frequency of predation events

•Predation by killer whales is likely to play a crucial role in regulating marine mammal populations in the North Pacific ecosystem1,2

1 Springer, A.M. et al. 2003, Proc. Natl. Acad. Sci. U.S.A.100:12223-12228 2 Williams, T.M et al. 2004, Ecology 85:3373–3384

•Rates of killer whale prey consump-tion are usually extrapolated from estimates of metabolic requirements. •Field data on predation rates for this area are currently limited

•Delineating the ecological role of mammal-eating killer whales requires precise knowledge about their abundance, dietary preferences, and the frequency of predation events

•Predation by killer whales is likely to play a crucial role in regulating marine mammal populations in the North Pacific ecosystem1,2

1 Springer, A.M. et al. 2003, Proc. Natl. Acad. Sci. U.S.A.100:12223-12228 2 Williams, T.M et al. 2004, Ecology 85:3373–3384

•Field data on predation rates for this area are currently limited

Introduction Methods Results Conclusions

BACKGROUND: Killer whales in the North Pacific ecosystem

•Rates of killer whale prey consump-tion are usually extrapolated from estimates of metabolic requirements.

•Predation on some species can be very subtle and some kills may be missed using visual observations alone. This may bias data on prey preference and predation rates

►OBJECTIVE: to test whether monitoring killer whale sound production can help to detect predation events

•Mammal-eating killer whales feed on prey that can detect killer whale vocalizations and respond with anti-predator behaviour1

1 Deecke V.B. et al. 2002 Nature, 420:171-173

•These animals typically hunt in silence but vocalize following a successful attack2

2 Deecke V.B. et al. 2005 Anim. Behav. 69:395-405.

•These animals typically hunt in silence but vocalize following a successful attack2

2 Deecke V.B. et al. 2005 Anim. Behav. 69:395-405.

•Mammal-eating killer whales feed on prey that can detect killer whale vocalizations and respond with anti-predator behaviour1

1 Deecke V.B. et al. 2002 Nature, 420:171-173

Introduction Methods Results Conclusions

•Predation on some species can be very subtle and some kills may be missed using visual observations alone. This may bias data on prey preference and predation rates

►OBJECTIVE: to test whether monitoring killer whale sound production can help to detect predation events

BACKGROUND: Detecting killer whale predation in the field

500m

The rate of sound production is:

No. of sounds within 500m

(No. of minutes within 500m) x (No. of animals)

(Sounds per animal per minute)

•We counted the number of sounds produced while the animals were within 500m of the boat

•We documented any predatory behaviour and collected prey remains whenever possible

•We recorded underwater sound production near groups of killer whales in Southeast Alaska

•We measured the distance to the animals using laser rangefinders

•We recorded underwater sound production near groups of killer whales in Southeast Alaska•We documented any predatory behaviour and collected prey remains whenever possible

•We measured the distance to the animals using laser rangefinders

Introduction Methods Results Conclusions

500m

The rate of sound production is:

No. of sounds within 500m

(No. of minutes within 500m) x (No. of animals)

(Sounds per animal per minute)

•We counted the number of sounds produced while the animals were within 500m of the boat

Data Collection

0.0

0.5

1.0

1.5

Other behaviours (N=7)After kill (N=7)

Behaviour CategoryCalls p

er

an

imal p

er

min

ute

0.0

0.5

1.0

1.5

Other behaviours (N=7)After kill (N=7)

Behaviour CategoryCalls p

er

an

imal p

er

min

ute

See also: Deecke et al. 2005, Anim. Behav. 69:395-405

Kruskall Wallis: p = 0.028

Time (s)

Fre

qu

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cy (

kH

z)

5

10

15

1 32 40Time (s)

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kH

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Introduction Methods Results Conclusions

Time (s)

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►mammal-eating killer whales consistently emit pulsed calls after a kill and these are good indicators of predatory activity.

Acoustic Detection of Kills: Pulsed Calls

Time (s)

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1 32 40Time (s)

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Introduction Methods Results Conclusions

►whistles are only produced rarely and are not consistently associated with predation events.

0.0

0.5

1.0

1.5

Other behaviours (N=7)After kill (N=7)

Behaviour Category

Wh

istl

es p

er

an

imal p

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min

ute

0.0

0.5

1.0

1.5

Other behaviours (N=7)After kill (N=7)

Behaviour Category

Wh

istl

es p

er

an

imal p

er

min

ute

Kruskall-Wallis: p = 0.109

Acoustic Detection of Kills: Whistles

Time (s)

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kH

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1 32 40Time (s)

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Introduction Methods Results Conclusions

►mammal-eating killer whales typically echolocate during and after an attack and echolocation presents a useful tool to detect predation events.

0.0

0.5

1.0

1.5

Other behaviours (N=7)After kill (N=7)

Behaviour Category

Click t

rain

s p

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an

imal p

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min

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Time (s)

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kH

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1 32 40

0.0

0.5

1.0

1.5

Other behaviours (N=7)After kill (N=7)

Behaviour Category

Click t

rain

s p

er

an

imal p

er

min

ute

Kruskall-Wallis: p = 0.028

Acoustic Detection of Kills: Echolocation Clicks

Time (s)

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kH

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1 32 40

Introduction Methods Results Conclusions

Acoustic Detection of Kills: Killing, Ramming and Crushing Sounds

►KRaCS are generated when killer whales handle a prey animal or carcass. They may be some of the best indicators that an attack was successful.

0.0

0.5

1.0

2.5

Other behaviours (N=7)After kill (N=7)

Behaviour CategoryKR

aC

S p

er

an

imal p

er

min

ute

0.0

0.5

1.0

2.5

Other behaviours (N=7)After kill (N=7)

Behaviour CategoryKR

aC

S p

er

an

imal p

er

min

ute

Kruskall-Wallis: p = 0.028

Time (s)

Fre

qu

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kH

z)

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1 32 40Time (s)

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Diet of West Coast Transients

•In the years 2003-2005, we followed 28 groups of transient killer whales for a total of 115 hrs while monitoring their sound production. •We documented a total of 22 successful attacks. The prey species could be identified in 12 attacks

•This is equivalent to a predation rate of 1.01 successful attacks per killer whale per day (when feeding on pinnipeds and small cetaceans)

•In the years 2003-2005, we followed 28 groups of transient killer whales for a total of 115 hrs while monitoring their sound production.

Unidentified marine mammal: 45%

Harbour seal32%

Steller sea lion5%

Harbour porpoise18%

Dall’s porpoise: 0%Sea otter: 0%

Diet of West Coast Transients

Dedicated acoustic follows (N=22)

•We documented a total of 22 successful attacks. The prey species could be identified in 12 attacks

Diet of West Coast Transients

Observer Reports(N=16) Harbour porpoise: 0%

Sea otter: 7%

Harbour seal36%

Steller sea lion36%

Dall’s porpoise21%

•This is equivalent to a predation rate of 1.01 successful attacks per killer whale per day (when feeding on pinnipeds and small cetaceans)

Diet of West Coast Transients

•We documented a total of 22 successful attacks. The prey species could be identified in 12 attacks

Estimating Predation Rates: Preliminary results

Introduction Methods Results Conclusions

Preliminary data suggest that killer whales consume the equivalent of one harbour seal per day. Killer whale predation has a significant potential impact on populations of pinnipeds and cetaceans in the North Pacific.

•Pulsed calls and KRaCS are consistently associated with kills

•Relying on surface behaviour alone may lead to missed predations events and may bias the prey spectrum towards larger and faster prey that are more difficult to subdue

•Acoustic monitoring presents a powerful tool to detect killer whale predation in the field

Preliminary data suggest that killer whales consume the equivalent of one harbour seal per day. Killer whale predation has a significant potential impact on populations of pinnipeds and cetaceans in the North Pacific.

Introduction Methods Results Conclusions

•Pulsed calls and KRaCS are consistently associated with kills

•Relying on surface behaviour alone may lead to missed predations events and may bias the prey spectrum towards larger and faster prey that are more difficult to subdue

•Acoustic monitoring presents a powerful tool to detect killer whale predation in the field

CONCLUSIONS: acoustic detection of killer whale predation

How do you know that transients have made a kill?

Listen to the whales – they’ll probably let you know.

THANKS TO: