Accurate calculation of growth in long-lived species is challenging. When a large wild Japanese giant salamander (Andrias japonicus) is found, we are often asked, “How old is it?” But we cannot answer this for sure under few information of the growth.

Over the past 35 years we have conducted a survey of A. japonicus in the Ichikawa River, Hyogo Prefecture, Japan. We identified more than 1500 salamanders by photographs and 850 with PIT tags. In this presentation we try to estimate the growth of A. japonicus by analyzing a large quantity of long-term data.

We sampled 337 individuals with recapture intervals of more than 5 years. Their total lengths ranged from 145 to 1105 mm, mean 688±8 and median 690 mm. Growth rates ranged from -9.4 to 42.2, mean 5.4±0.4 and median 3.8 mm/year. They decreased gradually with age and significantly divided into 3 groups by each initial total length: 200 - 500, 500 - 700, and 700 - 1100 mm. Moreover, several individuals became smaller and smaller.

The individual with the longest recapture interval increased in length from 690 to 860 mm over 36.6 years. How old is this Japanese giant salamander?