Recovery plan for an exploited species, southern bluefin tuna |
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Authors: | M Mori T Katsukawa H Matsuda |
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Institution: | (1) Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo 164-8639, Japan Tel. +81-3-5351-6491; Fax +81-3-5351-6492 e-mail: mmori@ori.u-tokyo.ac.jp, JP;(2) Ocean Research Institute, University of Tokyo, Tokyo, Japan, JP |
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Abstract: | Southern bluefin tuna (SBT) were heavily depleted in the mid-1980s, and the fishing quota has been restricted since 1985.
As a result of this restriction and protection of immature individuals, spawning stock biomass (SSB) recently has shown a
slight increase. The Commission for the Conservation of Southern Bluefin Tuna (CCSBT) has the target of recovering SSB to
the 1980 level by 2020. We investigated whether SBT populations will recover and reach the target level set by CCSBT. Our
projection shows that the SSB of the SBT will temporarily decrease again after 1999. This temporary decrease of SSB does not
always mean failure of the recovery plan, because the SSB trend is highly vulnerable to age-composition dynamics. The SBT
is an example of this. The number of mature SBT was small during the 1980s because of overfishing. Thus, the number of eggs
that were spawned by these mature SBT was small in these years, and when these small numbers of immature fish become mature,
the SSB will decrease again. We call this effect the inverse baby-boom effect. The inverse baby-boom effect may be common
for managed bioresources that have once been overexploited. We also examine the use of spawning potential (SP) and SSB as
an index of stock recovery.
Received: August 17, 2000 / Accepted: March 19, 2001 |
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Keywords: | Spawning stock biomass (SSB) Spawning potential (SP) Inverse baby-boom effect |
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