SC/F16/JR55

Preliminary report on progress in earplug-based age
determination of sei whales collected during 2002 to2013 JARPNII surveys
TAKEHARU BANDO1, HIKARI MAEDA2, YUICHIRO ISHIKAWA3, TOSHIYA KISHIRO2, HIDEHIRO KATO3
1

Institute of Cetacean Research, Toyomi-cho 4-5, Chuo-ku, Tokyo 104-0055, Japan
National Research Institute of Far Seas Fisheries 2-12-4, Fukuura, Kanazawa, Yokohama, Kanagawa
236-8648, Japan
3
Tokyo University of Marine Science and Technology, 5-7, Konan 4, Minato-ku, Tokyo 108-8477, Japan
Contact e-mail: bando@cetacean.jp
2ABSTRACTCounting the number of growth layers in earplugs is the standard method for age determinationof sei whales. The objective of this note is to report the progress of age determination of sei
whales collected during 2002 to 2013 JARPNII surveys. Earplugs were collected carefully fromall whales sampled and laboratory work was carried out to count growth layers. Readability ofsexually-immature sei whale earplugs was 52.8% for males and 49.2% for females. Readabilityof mature animal was higher than immature, 71.0% and 64.5% for males and females,respectively. Readability of all samples was 63.0%. Studies on spatial and temporal segregation,
feeding ecology and population dynamics of western North Pacific sei whales will be conductedin the future, based on age data.
SAMPLES AND METHOD FOR AGE DETERMINATION
Earplugs were collected from 1,084 sei whales (513 males and 571 females) sampled during 2002 to 2013
JARPNII surveys. The method of collection of earplugs and age determination for sei whale is almost thesame as that used for common minke whale (Maeda et al., 2016: SC/F16/JR53). The left and rightearplugs were collected carefully, and immediately fixed in 10% formalin solution until age
determination. In the laboratory, the flat along the central axis of the earplug was cut using a sharp blade,then it was ground on a wet stone to expose the neonatal line and growth layers. Growth layers werecounted under water using stereoscopic microscope.
A year of age was defined as one pair of the light and dark laminae in the core. Earplugs collected during
2002 to 2011 were read by one reader (Ishikawa), and samples collected in 2012 and 2013 were read byanother reader (Maeda). An inter-reader calibration experiment, following the method of Kitakado et al.
(2013), is planned for the near future.
AGE READABILITY
Readability of immature sei whale earplugs was 52.8% for males and 49.2% for females. Readability ofearplugs in mature animal was higher, 71.0% and 64.5% for males and females, respectively (Table 1).
Readability of all samples was 63.0%, which was higher than 44.1% observed in common minke whale(Maeda et al., 2016: SC/F16/JR53). Figure 1 shows readability of earplugs by body length class and sex.
Readability gradually increased with body length.
ANALYSIS TO BE CONDUCTEDAs mentioned above an inter-reader calibration exercise will be conducted. Biological parameters such as
age distribution, growth curve and age at sexual maturity will be estimated based on the new age data.
Furthermore, studies on spatial and temporal segregation, feeding ecology and population dynamics will
be conducted in the near future based on age data.

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REFERENCE
Kitakado, T., Lockyer, C. and Punt, E. A. 2013. A statistical model for quantifying age reading errors and its application to theAntarctic Minke whales. J. Cetacean Res. Manage. 13(3): 181-190.
Maeda, H., Bando, T., Kishiro, T., Kitakado, T. and Kato, H. Basic information of earplug as age character of common minke
whales in western North Pacific. Paper SC/F16/JR53 presented to the JARPNII special permit expert panel review workshop,Tokyo, February 2016 (unpublished). 10pp.

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Table 1. Number of samples and age readability of sei whales collected during 2002 to 2013 JARPN IIsurveys.
Number ofwhales
Male161
Female132
Male352
Female439
Male513
Female5711084
Sex

Immature
MatureCombined
Total

Number of whales withreadable earplugs
8565250283
335
348683

80

500

All

400

60300

40200

20100

n

Readability (%)

100

Readability(%)
52.8
49.2
71.0
64.5
65.3
60.9
63.0

00891011121314
Body length class (m)1516100

500

80

400

60

300

40200

20100

n

Readability (%)

Male00891011121314
Body length class (m)1516100

500

80

400

60300

40200

20100

n

Readability (%)

Female00891011121314
Body length class (m)1516

Figure 1. Age readability of sei whales collected during 2002 to 2013 JARPNII surveys by body lengthclass and sex.

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