SEASONAL CHANGES IN THE EARPLUG GERMINAL LAYERS OF NORTH PACIFIC COMMON MINKE WHALES

Abstract

We investigated the annual accumulation rate of the most recently formed layer of earplugs, the germinal layer (GL), of the North Pacific common minke whales, which is important for age estimation. The pale GLs from Kushiro in September and October were found to be significantly thicker than those from Ayukawa in April and May. The results suggest that the pale lamina accumulated during an approximately six-month period from spring to autumn in their feeding season. This was consistent with the hypothesis that one pale and one dark lamina, comprising one growth layer group, are formed annually in this species.