© 2004 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
Estimating migration rates from two tag–release/one recovery experiments
a Ocean Research Institute, the University of Tokyo 15-1 Minamidai, Nakano-ku, Tokyo 164-8639, Japan
b Tokyo University of Fisheries 4-5-7 Konan, Minato-ku, Tokyo 108-8477, Japan.
*Correspondence to K. Shirakihara: tel: +81 3 5351 6493; fax: +81 3 5351 6492. e-mail: shirak{at}ori.u-tokyo.ac.jp.
We propose a method for estimating migration (movement) rates from two tag–release/one recovery experiments, regardless of tag-shedding or incomplete tag-reporting which are major problems when tag–recovery techniques are applied to commercially exploitable populations. The entire survey area is divided into multiple strata in advance. The first release is limited to one stratum; then, the second release occurs in every stratum. Recoveries from both releases occur in every stratum. The migration rate between the time of the first and second release is estimated together with its variance. To check the applicability of our method, we applied it to tag–recovery data for skipjack tuna from various places at different times and unequal time intervals. The precision of the estimates was low and the coefficient of variation was 22.6–42.1% because of the small number of recoveries. The experimental design necessary to improve precision is discussed.
Keywords: migration rate, movement, skipjack tuna, tagging experiment
Received 31 July 2003; accepted 5 January 2004.