Transcript Deecke - North Pacific Research Board

Studying Killer Whale Predation in the Field
A Sound Approach to Detecting
Kills
Volker B. DEECKE
John K.B. FORD
Peter J.B. SLATER
Introduction
Methods
Results
Conclusions
BACKGROUND: Killer whales in the North Pacific ecosystem
•Predation by killer whales is likely to play a crucial role in regulating
marine mammal populations in the North Pacific ecosystem1,2
•Delineating the ecological role of mammal-eating killer whales requires
precise knowledge about their abundance, dietary preferences, and the
frequency of predation events
•Rates of killer whale prey consumption are usually extrapolated from
estimates of metabolic requirements.
•Field data on predation rates for this
area are currently limited
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
Introduction
Methods
Results
Conclusions
BACKGROUND: Detecting killer whale predation in the field
•Mammal-eating killer whales feed
on prey that can detect killer whale
vocalizations and respond with antipredator behaviour1
•These animals typically hunt in
silence but vocalize following a
successful attack2
•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
1 Deecke V.B. et al. 2002 Nature, 420:171-173
2 Deecke V.B. et al. 2005 Anim. Behav. 69:395-405
69:395-405..
Introduction
Methods
Results
Conclusions
Data Collection
•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
•We counted the number of sounds produced
while the animals were within 500m of the boat
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)
Introduction
Methods
Results
Conclusions
Acoustic Detection of Kills: Pulsed Calls
Frequency (kHz)
15
10
5
Calls per animal per minute
0
1
2
Time (s)
3
4
1.5
Kruskall Wallis: p = 0.028
►mammal-eating killer whales consistently
emit pulsed calls after a kill and these are
good indicators of predatory activity.
1.0
0.5
0.0
Other behaviours (N=7)
After kill (N=7)
Behaviour Category
See also: Deecke et al. 2005, Anim. Behav. 69:395-405
Introduction
Methods
Results
Conclusions
Acoustic Detection of Kills: Whistles
Frequency (kHz)
15
10
5
Whistles per animal per minute
0
1
2
Time (s)
3
4
1.5
Kruskall-Wallis: p = 0.109
►whistles are only produced rarely and are
not consistently associated with predation
events.
1.0
0.5
0.0
Other behaviours (N=7)
After kill (N=7)
Behaviour Category
Introduction
Methods
Results
Conclusions
Acoustic Detection of Kills: Echolocation Clicks
Frequency (kHz)
15
10
5
Click trains per animal per minute
0
1
2
Time (s)
3
4
1.5
Kruskall-Wallis: p = 0.028
►mammal-eating killer whales typically
echolocate during and after an attack and
echolocation presents a useful tool to
detect predation events.
1.0
0.5
0.0
Other behaviours (N=7)
After kill (N=7)
Behaviour Category
Introduction
Methods
Results
Conclusions
Acoustic Detection of Kills: Killing, Ramming and Crushing Sounds
Frequency (kHz)
15
10
5
KRaCS per animal per minute
0
1
2
Time (s)
3
4
2.5
Kruskall-Wallis: p = 0.028
►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.
1.0
0.5
0.0
Other behaviours (N=7)
After kill (N=7)
Behaviour Category
Introduction
Methods
Results
Conclusions
Estimating Predation Rates: Preliminary results
•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
Diet of West Coast
Transients
Observer
Dedicated
acoustic
Reports
follows
(N=16)
(N=22)
Harbour seal
32%
Harbour seal
36%
Harbour porpoise
18%
Steller sea lion
36%
5%
Dall’s porpoise: 0%
Harbour
Sea otter:
porpoise:
0% 0%
Dall’s porpoise
Unidentified
Sea otter: 7%
marine mammal: 45%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)
Introduction
Methods
Results
Conclusions
CONCLUSIONS: acoustic detection of killer whale predation
•Pulsed calls and KRaCS
consistently associated with kills
are
•Acoustic monitoring presents a
powerful tool to detect killer whale
predation in the field
•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
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.
How do you know that transients have
made a kill?
Listen to the whales – they’ll probably
let you know.
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