Acoustically derived growth rates of sperm whales (Physeter macrocephalus) around Ischia and Ventotene Islands (Italy): preliminary results.

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INTRODUCTION
Measuring the size of animals and quantifying their growth are fundamental to answering many ecological questions.
The sperm whale (Physeter macrocephalus) is the largest odontocete cetacean existing today. This animal emits almost exclusively one type of sound called "click", used in
different circumstances and for different functions, including communication and echolocation. Clicks are multiple pulses (3 or more) at frequencies ranging from 5 to over 25
kHz, with high sound pressure level (greater than 223 dB) and high directionality. The type of the arrangement, frequency, intensity and duration of the clicks may provide
insights on behavior, while the range of the pulses in the same click (Inter Pulse Interval - IPI) seems to be related to the size of the emitting animal.
Acoustic methods for estimate the size of sperm whales by measuring the IPI of their clicks have been applied in some different studies; however, very few data on the growth
rate of sperm whale individuals in the Mediterranean Sea is available to date. We recently started to use to recordings collected around Ischia and Ventotene islands
(Tyrrhenian Sea), Italy, in order to estimate the size and the growth of sperm whales that have been photo-identified and recorded at least two times in two different years
between 2004 and 2012.
Here, we report the preliminary analysis on two individuals – one of unknown sex named PMODO.003 ‘Norma’ (Figure 1) and one immature male named PMODO.015
‘Brunone’ (Figure 2) – over a three year period (2004, 2005 and 2006). The entire dataset counts 60 photo-identified individuals, 20 of which resighted in different years.
Acoustically derived growth rates of sperm whales
(Physeter macrocephalus) around Ischia and
Ventotene Islands (Italy): preliminary results
Pace D.S.1,2, Miragliuolo A.2, Dernowski R.2, Vivaldi C.2 and Mussi B.2
1 University of Rome ‘La Sapienza’, Department of Environmental Biology – Rome, Italy
2 Oceanomare Delphis Onlus – Rome, Italy
METHODS
We analyzed a total of 22:36:07 of recordings, 11:07:36 related to ‘Norma’ e 11:28:31 related to
‘Brunone’.
The acoustic parameters used to characterize the sounds were:
1) Intensity of the acoustic wave (in dB), i.e. the amount of energy (P) which passes through, in
a second, the unit of surface area (S).
2) Rhythm. A number of different parameters were taken into account to assess the rhythms,
including:
- IPI - Inter Pulse Interval, i.e. the time intervals between pulses within a click.
- Cepstrum, i.e. according to the theory of the signals, the result of the "Fourier Transform"
(FFT) applied to the spectrum (in dB) of a signal.
- ICI (Inter Click Interval), i.e. the time interval between two clicks.
Different types of acoustic signals emitted by the two sperm whales were classified according
to ICI (usual click, creak, codas, etc.). Sequences of usual clicks were then selected to
measure IPIs. Each click within a sequence was identified, numbered sequentially and saved
in a separate file. A limited number of clicks (n=15 per year for each whale, i.e. 45 per whale),
out of a total of 283.932 clicks for both whales, was sorted out through a simple random
sampling. Selected clicks were initially ‘clean’ from background noises and then checked for
their suitability for the IPI analysis by the means of Audacity 2.0.1 software. Finally, IPIs were
manually derived through the ‘cross correlation’ function in Rainbow Click 4.06 and body length
estimated using different polynomial formulas:
TL=4,833+(1,453*IPI)-(0,001*IPI2) (Gordon, 1991) (TL formula 1)
TL=9,75-(0,521*SL)+(0,068*SL2)+(0,0057*SL3) (Gordon, 1991) (TL formula 2)
TL=(1,258*IPI)+5,736 (Growcott, 2011) (TL formula 3)
Where TL= total length in meters, IPI=Inter Pulse Interval in milliseconds, SL=spermaceti
length in meters.
NORMA BRUNONE
RESULTS
Table 1 and 2 report IPI values, spermaceti length and total body length estimates for Norma
and Brunone, respectively.
Unconcernedly from the applied formula, both whales showed:
• Similar estimated length in 2004 and different ones in 2006 (Figure 3 and 4);
• An increasing derived IPI over time (Figure 5) as well as a growth of the spermaceti
organ (Figure 6)
• A quicker growth rate between 2005 – 2006 than 2004 – 2005 (Table 3), with the
immature male Brunone seeming to grow up significantly faster than the other whale
Norma.
To proceed with the analysis of the other individuals of the dataset, we will use automatic
methods to generate IPIs in order to match results with our manually derived preliminary
finding.
Year Whale
Selected
clicks
IPI
Spermaceti
lenght (m)
Whale lenght (m)
Formula 1
(Gordon, 1991)
Whale lenght (m)
Formula 2
(Gordon, 1991)
Whale lenght (m)
Formula 3
(Growcott, 2011)
2004 Norma 5210 3,99 2,85 10,137 10,615 10,755
2004 Norma 13129 3,99 2,85 10,137 10,615 10,755
2004 Norma 13831 3,86 2,85 10,137 10,427 10,592
2004 Norma 15391 3,69 2,76 10,028 10,181 10,378
2004 Norma 15957 3,88 2,64 9,897 10,456 10,617
2004 Norma 17225 3,38 2,77 10,040 9,733 9,988
2004 Norma 18356 3,47 2,42 9,695 9,863 10,101
2004 Norma 20053 4,17 2,48 9,746 10,875 10,982
2004 Norma 26840 3,86 2,98 10,310 10,427 10,592
2004 Norma 34193 3,58 2,76 10,028 10,022 10,240
2004 Norma 34408 4,08 2,98 10,310 10,745 10,869
2004 Norma 39284 4,08 2,76 10,028 10,745 10,869
2004 Norma 42677 3,58 2,76 10,028 10,022 10,240
2004 Norma 44726 3,45 2,76 10,028 9,834 10,076
2004 Norma 50596 3,86 2,56 9,818 10,427 10,592
3,79±0,25 2,75±0,16 10,01±0,18 10,33±0,37 10,51±0,32
2005 Norma 478 4,08 2,92 10,228 10,745 10,869
2005 Norma 3853 4,08 2,92 10,228 10,745 10,869
2005 Norma 12037 4,31 3,08 10,456 11,077 11,158
2005 Norma 16661 3,79 2,71 9,972 10,326 10,504
2005 Norma 22347 3,99 2,85 10,137 10,615 10,755
2005 Norma 22639 3,74 2,67 9,929 10,253 10,441
2005 Norma 29761 3,97 2,84 10,124 10,586 10,730
2005 Norma 36218 3,85 2,75 10,017 10,412 10,579
2005 Norma 37759 3,65 2,61 9,867 10,123 10,328
2005 Norma 38238 4,08 2,92 10,228 10,745 10,869
2005 Norma 41612 4,08 2,92 10,228 10,745 10,869
2005 Norma 51047 4,29 3,06 10,426 11,048 11,133
2005 Norma 55191 3,61 2,58 9,837 10,065 10,277
2005 Norma 58274 3,9 2,79 10,064 10,484 10,642
2005 Norma 70895 3,88 2,77 10,040 10,456 10,617
3,95±0,21 2,83±0,15 10,12±0,19 10,56±0,30 10,71±0,26
2006 Norma 2068 4,08 2,92 10,228 10,745 10,869
2006 Norma 2153 4,08 2,92 10,228 10,745 10,869
2006 Norma 4171 4,22 3,02 10,367 10,947 11,045
2006 Norma 6413 4,4 3,15 10,565 11,207 11,271
2006 Norma 8121 4,08 2,92 10,228 10,745 10,869
2006 Norma 11569 4,08 2,92 10,228 10,745 10,869
2006 Norma 11793 4,08 2,92 10,228 10,745 10,869
2006 Norma 13138 4,08 2,92 10,228 10,745 10,869
2006 Norma 13950 4,31 3,08 10,456 11,077 11,158
2006 Norma 14707 4,31 3,08 10,456 11,077 11,158
2006 Norma 15604 4,24 3,03 10,381 10,976 11,070
2006 Norma 16276 4,08 2,92 10,228 10,745 10,869
2006 Norma 16331 4,4 3,15 10,565 11,207 11,271
2006 Norma 16779 3,89 2,78 10,052 10,470 10,630
2006 Norma 18573 4,13 2,95 10,268 10,817 10,932
4,16±0,14 2,98±0,10 10,31±0,14 10,87±0,21 10,97±0,18
2004 AVERAGE±SD
2005 AVERAGE±SD
2006 AVERAGE±SD
Tab. 1
Year Whale
Selected
clicks
IPI
Spermaceti
lenght (m)
Whale lenght (m)
Formula 1
(Gordon, 1991)
Whale lenght (m)
Formula 2
(Gordon, 1991)
Whale lenght (m)
Formula 3
(Growcott, 2011)
2004 Brunone 931 3,88 2,77 10,040 10,456 10,617
2004 Brunone 1458 3,70 2,64 9,897 10,195 10,391
2004 Brunone 3564 3,72 2,66 9,918 10,224 10,416
2004 Brunone 3673 3,90 2,79 10,064 10,484 10,642
2004 Brunone 3806 3,87 2,77 10,040 10,441 10,604
2004 Brunone 4375 3,72 2,66 9,918 10,224 10,416
2004 Brunone 4551 3,87 2,77 10,040 10,441 10,604
2004 Brunone 5846 3,88 2,77 10,040 10,456 10,617
2004 Brunone 5913 3,88 2,77 10,040 10,456 10,617
2004 Brunone 7426 3,88 2,77 10,040 10,456 10,617
2004 Brunone 9115 3,72 2,66 9,918 10,224 10,416
2004 Brunone 10870 3,90 2,79 10,064 10,484 10,642
2004 Brunone 11638 3,90 2,79 10,064 10,484 10,642
2004 Brunone 14841 3,88 2,77 10,040 10,456 10,617
2004 Brunone 15960 3,85 2,75 10,017 10,412 10,579
3,84±0,08 2,74±0,05 10,01±0,08 10,39±0,11 10,56±0,10
2005 Brunone 1098 4,20 3,00 10,338 10,918 11,020
2005 Brunone 2134 3,86 2,76 10,028 10,427 10,592
2005 Brunone 2381 4,01 2,87 10,162 10,643 10,781
2005 Brunone 2458 4,08 2,92 10,228 10,745 10,869
2005 Brunone 2876 4,04 2,89 10,188 10,687 10,818
2005 Brunone 3029 4,01 2,87 10,162 10,643 10,781
2005 Brunone 4512 4,08 2,92 10,228 10,745 10,869
2005 Brunone 5177 3,88 2,77 10,040 10,456 10,617
2005 Brunone 5671 3,88 2,77 10,040 10,456 10,617
2005 Brunone 8344 4,17 2,98 10,310 10,875 10,982
2005 Brunone 9580 3,99 2,85 10,137 10,615 10,755
2005 Brunone 9656 4,08 2,91 10,214 10,745 10,869
2005 Brunone 9827 4,04 2,89 10,188 10,687 10,818
2005 Brunone 10568 3,88 2,77 10,040 10,456 10,617
2005 Brunone 11480 4,13 2,95 10,268 10,817 10,932
4,02±0,11 2,87±0,08 10,17±0,10 10,66±0,16 10,80±0,14
2006 Brunone 10220 4,39 3,14 10,549 11,192 11,259
2006 Brunone 24299 4,38 3,13 10,533 11,178 11,246
2006 Brunone 30895 4,17 2,98 10,310 10,875 10,982
2006 Brunone 61399 4,35 3,11 10,502 11,135 11,208
2006 Brunone 66821 4,35 3,11 10,502 11,135 11,208
2006 Brunone 76207 4,12 2,95 10,268 10,802 10,919
2006 Brunone 78110 4,17 2,98 10,310 10,875 10,982
2006 Brunone 79283 4,31 3,08 10,456 11,077 11,158
2006 Brunone 94535 4,35 3,11 10,502 11,135 11,208
2006 Brunone 95424 4,35 3,11 10,502 11,135 11,208
2006 Brunone 99228 4,33 3,1 10,486 11,106 11,183
2006 Brunone 102748 4,33 3,1 10,486 11,106 11,183
2006 Brunone 107441 4,26 3,05 10,411 11,005 11,095
2006 Brunone 109059 4,11 2,94 10,255 10,788 10,906
2006 Brunone 109503 4,33 3,1 10,486 11,106 11,183
4,29±0,10 3,07±0,07 10,44±0,10 11,04±0,14 10,13±0,12
2004 AVERAGE±SD
2005 AVERAGE±SD
2006 AVERAGE±SD
Tab. 2
Fig. 1
Fig. 2
2004
2005
2006
TL1 - Gordon 1991
10,00718
10,11502
10,31187
TL2 - Gordon 1991
10,32551
10,55675
10,87017
TL3 - Growcott 2011
10,56382
10,70510
10,96928
9,6
9,8
10,0
10,2
10,4
10,6
10,8
11,0
11,2
Body lenght (m)
Estimated body lenght by year NORMA
Fig. 3
2004
2005
2006
TL1 - Gordon 1991
10,01189
10,16782
10,43669
TL2 - Gordon 1991
10,39777
10,65790
11,04797
TL3 - Growcott 2011
10,56672
10,79316
11,13282
9,6
9,8
10,0
10,2
10,4
10,6
10,8
11,0
11,2
Body lenght (m)
Estimated body lenght by year - BRUNONE
Fig. 4
2,74±0,05
2,87±0,08
3,07±0,07
2,75±0,16
2,83±0,15
2,98±0,10
2,5
2,6
2,7
2,8
2,9
3
3,1
2004
2005
2005
lenght (m)
Spermaceti lenght variation by year
NORMA
BRUNONE
Fig. 6
3,79±0,25
3,95±0,21
4,16±0,14
3,84±0,08
4,02±0,11
4,29±0,10
3,5
3,6
3,7
3,8
3,9
4
4,1
4,2
4,3
4,4
2004
2005
2005
time (ms)
IPI variation by year
NORMA
BRUNONE
Fig. 5
TL Formula 1 TL Formula 2 TL Formula 3 TL Formula 1 TL Formula 2 TL Formula 3
2004-2005 10,77 cm 23,12 cm 14,13 cm 15,60 cm 26,01 cm 22,64 cm
2005-2006 19,70 cm 31,30 cm 26,42 cm 26,90 cm 39,01 cm 33,97 cm
TOT (2004-2006) 30,47 cm 54,42 cm 40,55 cm 42,50 cm 65,02 cm 56,61 cm
Growth rate 0,10 0,18 0,13 0,14 0,21 0,19
NORMA
BRUNONE
YEAR
Tab. 3
www.oceanomaredelphis.org
ACKNOWLEDGEMENTS
This project received funding from Ocean Care (CH)
and the Riccardo Domenici Association (Italy); their
support is gratefully acknowledged.
Thanks to Massimo Azzali for the acoustic supervision.