decaf – density estimation for cetaceans from passive ... · decaf – density estimation for...

DECAF – Density Estimation for Cetaceans from passive

Acoustic Fixed sensors

Presented by: Len Thomas

JIP Program Review Meeting October 28-30, 2008

JIP program review, October 28JIP program review, October 28--30 200830 2008

About the project• 3 year project: May 2007 – 2010• Funded under NOPP by JIP and NOAA.

Leveraging previous work funded by ONR.• Investigators:

– University of St Andrews: Len Thomas, David Borchers, Tiago Marques, Catriona Stephenson

– US Naval Undersea Warfare Center: Dave Moretti, Jessica Ward, Nancy DiMarzio, Ron Morrissey

– US Space and Naval Warfare Systems Center: Steve Martin– University of Oregon: Dave Mellinger, Elizabeth Küsel– Woods Hole Oceanographic Institution: Peter Tyack

• Steering group:– Walter Zimmer, Jay Barlow, Steve Buckland


Goals1. Develop methods for estimating the density of

cetacean species from fixed passive acoustic devices.

2. Demonstrate the utility and generality of the methods by implementing them in a set of key test case studies.

3. Promote adoption of the new methods in the marine mammal research community by

a. publishing results in the peer-reviewed literatureb. archiving data and results in publicly available

electronic storehousesc. holding workshops open to all interested

researchers


Why estimate absolute density?

• Why not use an easier-to-obtain, relative measure such as detections per unit time?

• Relative measures not good enough when:– population size is of intrinsic interest– doing long term monitoring– regulatory framework – need to determine “take limits”

and “takes”– need to determine population effect of potentially

harmful activity (e.g., via BACI)– want priors on real-time monitoring studies


• Minke whales at PMRF• Sperm whales at AUTEC

• Humpback whales at PMRF

Case studies

All use US Navy instrumented testing ranges

( )

• Beaked whales at AUTEC

• Sperm whales from a single sensor at AUTEC


Conceptual framework

How to estimate whale density from fixed passive acoustic monitoring


Focus here on cue-based methods

• We have K hydrophones• operating for T hours• and we detect n cues

• How many whales are there? or, equivalently• What is the whale density?

(numbers per unit area)

Cue=discrete, identifiable vocalization – e.g., click, song unit, etc.


Example: Beaked whales at AUTEC

K=82 hydrophones

T=5,062 minutes

n= 2,943,789 Mesoplodon densirostriswhale clicks detected

What is the average beaked whale density at AUTEC over this 6-day period?


Estimating density (1)• Let w be a distance beyond which no cues

can be detected.• If all cues with distance w

are detected• then density of cues per

unit time is

TwKnDc 2π

=0 2 4 6 8 10

0.0

0.2

0.4

0.6

0.8

1.0

distancep(

dete

ct)

example: w=7


Estimating density (2)• but, realistically, not all cues within w will

be detected.

• Let the average proportion detected be p.

• Then,

TpwKnDc 2π

=0 2 4 6 8 10

0.0

0.2

0.4

0.6

0.8

1.0

distance

p(de

tect

)

example: p=0.12


Estimating density (3)• Also, most detectors have a non-negligible

false positive rate.• Let c be the proportion of false positive

detections. • Then,

TpwKcnDc 2

)1(π−

=


Estimating density (4)• Lastly, to convert density of cues to

density of animals, we need the cue rate –number of calls per unit time.

• Let r be cue rate. • Then,

TprwKcnD 2

)1(π−

=


Canonical formula

So, we need estimates of 3 quantities:• p – the detection probability• r – the cue rate• c – the proportion of false positive

detections

rpTwKcnD

ˆˆ)ˆ1(ˆ

2π−

=

e.g., hand calibrate a sample of data

e.g., tagging study or focal follow

lots of ways…


0 1 2 3 4

1020

3040

5060

distance

n.de

tect

ed

0 1 2 3 4

1020

3040

5060

distance

n.de

tect

ed

0 1 2 3 4

1020

3040

5060

distance

true

n

Estimating p using distance sampling• Need (a) distances to detected cues, and

(b) “randomly” placed hydrophones

12

34

ππ3

π5

π7

0 1 2 3 40.0

0.2

0.4

0.6

0.8

1.0

distance

p(de

tect

)


What if you can’t get distances and/or don’t have random hydrophones?

• Lots of options – see poster on DECAF web site

• (or chat to me anytime!)• Also covers individual

and group-based (as opposed to cue-based) methods – don’t need cue rate (but may need group size)!


Estimating p for beaked whales at AUTEC

• Can’t get distances (narrow beam pattern)• Used data from tagged animals

– Dives geo-referenced– Clicks from diving animals associated with those

received on surrounding range hydrophones

– Preliminary estimate of with w=7km– Need to adjust for different ambient noise conditions

057.0ˆ =p


Estimating cue rate for beaked whales at AUTEC

• Use tagged whales• Do “tag-on” effect – confirmed by 72 hour

dataset from Robin Baird• Mean cue rate 0.41 clicks/second.


Estimating false positive rate forbeaked whales at AUTEC

• Hand checked 30 10-minutes samples from all hydrophones

• False positive rate (for simple FFT-based detector used) 0.44 or 0.49 depending on assumptions made about calls ambiguous even to human operator


Preliminary density estimate for beaked whales at AUTEC

rpTwKcnD

ˆˆ)ˆ1(ˆ

2π−

=

41.00573.0303720782)443.01(2984379

2 ×××××−×

=π

21000kmper whales18=

• Note (1) preliminary estimate; (2) no variance!


Progress on other case studies• Humpback whales

Niihau Kauai

Localizations of manually detected songs, 10 minute period 15 Apr 07

range hydrophones

song locations

• Many are far from the range and/or close together, making localization difficult

• Assumption of known distribution with respect to hydrophones not justified

• Therefore, not the “simple”case study we thought it would be


Progress on other case studies• Minke whales at PMRF

– Found within range hydrophones, so provides a better “simple” case study

– 10 minute test datasets have been manually analyzed and we are developing automated detectors and localizers

– Call rates currently unknown• Sperm whales at AUTEC

– Test datasets identified, and preliminary analysis has been conducted

• Sperm whale single sensor– Postdoc Küsel to start at OSU soon


Open workshops on estimating cetacean density from passive

acoustics – You’re invited!• San Diego, California

– 16th July 2009– Informal, one-day workshop, after

distance sampling training workshop

• Pavia, Italy– 13th September 2009– One day workshop, linked to

Detection, Classificiation and Localization meeting

• More details on DECAF web site

COME TO AN ACOUSTIC DENSITY

ESTIMATION WORKSHOP


Conclusions

• Obtaining robust density estimates from fixed PAM is hard…

• … but it is possible

• Often auxiliary information is required– Tagging studies / Visual-acoustic data


Future priorities“Beyond DECAF”…

• Further case studies– vertical arrays– other biological systems– …

• Transition– software, training workshops…

• Survey design


For more information• DECAF web site

http://www.creem.st-and.ac.uk/decaf/– Background white paper– Marques et al. Poster paper

• Nice PAM overview paper:– Mellinger, D. K., Stafford, K. M., Moore, S. E.,

Dziak, R. P. and Matsumoto, H. 2007. An overview of passive acoustic observation methods for cetaceans. Oceanography 20: 36-45.

• Come to the workshops• Come talk with me!

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