Whale age at sexual maturity is one of the most
important biological parameters that can be used in stock management and
population analysis. Earplugs have been widely used as an indicator of age
among rorquals. It has also been accepted that the transition phase in the
earplug can be used as an indicator of age at sexual maturity in fin whales,
sei whales, and Antarctic minke whales. This study aimed to provide further
insight into the utility of the transition phase as an indicator of age at
sexual maturity in the North Pacific common minke whales, which has not yet
been clarified. The relationship between sexual maturity and transition phase
in earplugs was examined using 981 readable earplugs from common minke whales
that were sampled at the JARPN and JARPN II scientific permit survey platform
in the western North Pacific from 1994 to 2011. The transition phase was
recognized in 53.2% of mature males and in 58.6% of mature females. Most whales
in which the transition phase was recognized in the earplug were sexually
mature. A significant correlation was found between the number of corpora and
time after sexual maturation, as revealed by the transition phase,
demonstrating that the transition phase is a valid indicator of age at sexual
maturity in common minke whales. However, it was difficult to recognize the
transition phase in whales that had recently attained sexual maturity because
insufficient time had elapsed since its formation. To avoid potential bias, the
use of earplugs as an indicator of age should be restricted to whales more than
12 years old.
References
[1]
Lockyer, C. (1984) Age Determination by Means of the Earplug in Baleen Whales. Report of the International Whaling Commission, 34, 692-696.
[2]
Lockyer, C. (1984) Review of Baleen Whale (Mysticeti) Reproduction and Implications for Management. Report of the International Whaling Commission, 6, 27-50.
[3]
Purves, P. E. (1955) The Wax Plug in the External Auditory Meatus of the Mysticeti. Discovery Reports, 27, 293-302.
[4]
Lillie, D.G. (1910) Observation on the Anatomy and General Biology of Some of Members of the Lager Cetacea. Proceedings of the Zoological Society of London, 80, 769-792. https://doi.org/10.1111/j.1096-3642.1910.tb01916.x
[5]
Ichihara, T. (1959) Formation Mechanism of Ear Plug in Baleen Whales in Relation to Glove-Finger. Scientific Reports of the Whales Research Institute, 14, 107-135.
[6]
Roe, H.S.J. (1967) Seasonal Formation of Laminae in the Ear Plug of the Fin Whale. Discovery Reports, 35, 1-30.
[7]
Ohsumi, S. (1964) Examination on Age Determination of the Fin Whales. Scientific Reports of the Whales Research Institute, 18, 49-88.
[8]
Lockyer, C. (1972) Maturity of the Southern Fin Whale (Balaenoptera physalus) Using Annual Layer Counts in the Ear Plug. ICES Journal of Marine Science, 34, 276-294. https://doi.org/10.1093/icesjms/34.2.276
[9]
Gabriele, C.M., Lockyer, C., Straley, M.J., Jurasz, M.C. and Kato, H. (2010) Sighting History of a Naturally Marked Humpback Whale (Megaptera novaeangliae) Suggests Ear Plug Growth Layer Groups Are Deposited Annually. Marine Mammal Science, 26, 443-450. https://doi.org/10.1111/j.1748-7692.2009.00341.x
[10]
Ichihara, T. (1964) Prenatal Development of Ear Plug in Baleen Whales. Scientific Reports of the Whales Research Institute, 18, 29-48.
[11]
Maeda, H., Kawamoto, T. and Kato, H. (2013) A Study on the Improvement of Age Estimation in Common Minke Whales using the Method of Gelatinized Extraction of Earplug. NAMMCO Scientific Publications, 10, 17. https://doi.org/10.7557/3.2609
[12]
Maeda, H., Bnado, T., Kishiro, T., Kitakado, T. and Kato, H. (2016) Basic Information of Earplugs as Age Character of Common Minke Whales in Western North Pacific. Paper SC/F16/JR53 Presenter to the JARPNⅡ Special Expert Panel Final Review Workshop, February 2016 (Unpublished), 15 p.
[13]
Lockyer, C. (1974) Investigation of the Ear Plug of the Southern Sei Whale, Balaenopteraborealis, as a Valid Means of Determining Age. Journal du Conseil, 36, 71-81. https://doi.org/10.1093/icesjms/36.1.71
[14]
Kato, H. (1983) Some Considerations on the Decline in Age at Sexual Maturity of the Antarctic Minke Whale. Report of the International Whaling Commission, 33, 393-399.
[15]
Lockyer, C. (1977) A Preliminary Study of Variations in Age at Sexual Maturity of the Fin Whale with Year Class in Six Areas of the Southern Hemisphere. Report of the International Whaling Commission, 27, 141-147.
[16]
Lockyer, C. (1981) The Age at Sexual Maturity in Fin Whales off Iceland. Report of the International Whaling Commission, 31, 389-393.
[17]
Masaki, Y. (1976) Biological Studies on the North Pacific Sei Whale. Bulletin Far Seas Fisheries Research Laboratory, 14, 1-104.
[18]
Lockyer, C. and Martin, A.R. (1983) The Sei Whale off Western Iceland. II. Age, Growth and Reproduction. Report of the International Whaling Commission, 33, 465-476.
[19]
Masaki, Y. (1979) Yearly Changes of the Biological Parameters for the Antarctic Minke Whale. Report of the International Whaling Commission, 29, 225-251.
[20]
Best, P.B. (1982) Seasonal Abundance, Feeding, Reproduction, Age and Growth in Minke Whale off Durban (with Incidental Observations from the Antarctic). Report of the International Whaling Commission, 32, 759-786.
[21]
Kato, H. (1985) Further Examination of the Age at Sexual Maturity of the Antarctic Minke Whale as Determined from Earplug Studies. Report of the International Whaling Commission, 35, 273-277.
[22]
Ohsumi, S. (1986) Earplug Transition Phase as an Indicator of Sexual Maturity in Female Antarctic Minke Whales. Scientific Reports of the Whales Research Institute, 37, 17-30.
[23]
Lockyer, C. (1979) Changes in a Growth Parameter Associated with Exploitation of Southern Fin and Sei Whales. Report of the International Whaling Commission, 29, 191-143.
[24]
Kato, H. and Sakuramoto, K. (1991) Age at Sexual Maturity of Southern Minke Whales: A Review and Some Additional Analyses. Report of the International Whaling Commission, 41, 331-337.
[25]
Kishiro, T., Kato, H., Yoshida, H., Yasunaga, G., Tabata, S., Nakamura, G., Maeda, H., Inoue, S., Miyakawa, N., Okamoto, R., Oikawa, H., Watanabe, H., Iwasaki, T., Kanaji, Y., Minamikawa, S., Otani, H., Ishikawa, H., Kanda, N., Gokita, A., Yamazaki, K. and Yonehara, Y. (2010) Cruise Report of the Second Phase of the Japanese Whale Research Program under Special Permit in the Western North Pacific (JARPN II) in 2009 (Part 2)—Coastal Component off Kushiro. Paper SC/62/O6 Presented to the 62nd IWC Scientific Committee Meeting, 13.
[26]
Zenitani, R. (2011) Long-Term Change of the Age at Sexual Maturity and Ecological Analysis in Antarctic Minke Whale. Dr. Scient Thesis, Tokyo University of Marine Science and Technology, 106. (In Japanese)
[27]
Kato, H. (1992) Body Length, Reproduction and Stock Separation of Minke Whales of Northern Japan. Report of the International Whaling Commission, 42, 443-453.
