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 ecosystem 1,2 1 Springer, A.M. et al. 2003, Proc. Natl. Acad. Sci. U.S.A.100: 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 ecosystem 1,2 1 Springer, A.M. et al. 2003, Proc. Natl. Acad. Sci. U.S.A.100: Williams, T.M et al. 2004, Ecology 85:3373–3384 Field data on predation rates for this area are currently limited IntroductionMethodsResultsConclusions 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 behaviour 1 1 Deecke V.B. et al Nature, 420: These animals typically hunt in silence but vocalize following a successful attack 2 2 Deecke V.B. et al Anim. Behav. 69: These animals typically hunt in silence but vocalize following a successful attack 2 2 Deecke V.B. et al Anim. Behav. 69: Mammal-eating killer whales feed on prey that can detect killer whale vocalizations and respond with anti- predator behaviour 1 1 Deecke V.B. et al Nature, 420: IntroductionMethodsResultsConclusions 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 IntroductionMethodsResultsConclusions 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

Other behaviours (N=7)After kill (N=7) Behaviour Category Calls per animal per minute Other behaviours (N=7)After kill (N=7) Behaviour Category Calls per animal per minute See also: Deecke et al. 2005, Anim. Behav. 69: Kruskall Wallis: p = Time (s) Frequency (kHz) Time (s) Frequency (kHz) IntroductionMethodsResultsConclusions Time (s) Frequency (kHz) ► 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) Frequency (kHz) Time (s) Frequency (kHz) Time (s) Frequency (kHz) IntroductionMethodsResultsConclusions ► whistles are only produced rarely and are not consistently associated with predation events Other behaviours (N=7)After kill (N=7) Behaviour Category Whistles per animal per minute Other behaviours (N=7)After kill (N=7) Behaviour Category Whistles per animal per minute Kruskall-Wallis: p = Acoustic Detection of Kills: Whistles

Time (s) Frequency (kHz) Time (s) Frequency (kHz) IntroductionMethodsResultsConclusions ► mammal-eating killer whales typically echolocate during and after an attack and echolocation presents a useful tool to detect predation events Other behaviours (N=7)After kill (N=7) Behaviour Category Click trains per animal per minute Time (s) Frequency (kHz) Other behaviours (N=7)After kill (N=7) Behaviour Category Click trains per animal per minute Kruskall-Wallis: p = Acoustic Detection of Kills: Echolocation Clicks

Time (s) Frequency (kHz) IntroductionMethodsResultsConclusions 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 Other behaviours (N=7)After kill (N=7) Behaviour Category KRaCS per animal per minute Other behaviours (N=7)After kill (N=7) Behaviour Category KRaCS per animal per minute Kruskall-Wallis: p = Time (s) Frequency (kHz) Time (s) Frequency (kHz)

Diet of West Coast Transients In the years , 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 , we followed 28 groups of transient killer whales for a total of 115 hrs while monitoring their sound production. Unidentified marine mammal: 45% Harbour seal 32% Steller sea lion 5% Harbour porpoise 18% 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 seal 36% Steller sea lion 36% Dall’s porpoise 21% 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 IntroductionMethodsResultsConclusions

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. IntroductionMethodsResultsConclusions 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: COLLABORATORS: Lance G. Barrett-Lennard Graeme M. Ellis Craig O. Matkin Dena R. Matkin Jan M. Straley FUNDING: National Oceanic and Atmospheric Administration Alaska Fisheries Development Foundation North Pacific Universities Marine Mammal Research Consortium SUPPORT IN THE FIELD AND LAB: Douglas Chadwick Michael deRoos Steve Jeffries Vicky Livaditis Josh London Allyson Miscampbell Patrick Presi LOGISTIC SUPPORT: Alaska Marine Lines Glacier Bay National Park & Preserve The Communities of Gustavus, Juneau, and Petersburg