SWIMMING ABILITY OF JAPANESE EEL (Anguilla japonica) ELVERS

Abstract

 The Japanese eel, Anguilla japonica, elvers in their upstream migration period averaging 5.8cm total lengths, were examined for their swimming ability in an experimental flume. Our results are as follows: 1) The results of the elvers burst swimming speed were 36-56cm per second (6.4-10.0 body lengths cm/s). 2) It was observed that the elvers could not make progress against water currents greater than 50cm/s on their noses. Even slight advances were difficult. 3) Against less than 39cm/s water current, 68% of the elvers were able to make more than 30cm upstream progress. 4) These results indicated that most of the about 6cm elvers would not be able to ascend many standard stepped-pool type fishways in Japan. Therefore, for elvers to migrate successfully, it is necessary to regulate the water velocity in some places, or provide upstream migration facilities to accommodate the elvers’ climbing behavior. This would be essential at weirs of high flow velocity.