TITLE:
Utility of the Transition Phase in Earplugs of the North Pacific Common Minke Whale as an Indicator of Age at Sexual Maturity
AUTHORS:
Hikari Maeda, Yoshihiro Fujise, Toshiya Kishiro, Hidehiro Kato
KEYWORDS:
Common Minke Whale, Balaenoptera acutorostrata, Earplug, Age at Sexual Maturity, Transition Phase
JOURNAL NAME:
Open Journal of Animal Sciences,
Vol.7 No.4,
September
25,
2017
ABSTRACT: 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.