CoML Meeting at Washington D.C., October 23, 2003
According to NHK International News (in Japanese) on October 23, Japan Fisheries Agency regulated 2003 total allowable catch of Pacific chub mackerel. I frequently claimed that overfishing of chub mackerel is a strong impact on the stock (Matsuda et al. 1992). Fishing pressure on immature mackerels since 1990s was much stronger than that during 1970-1989. Using average fishing mortality from 1993 to 1999, the stock will not be recovered within the next 20 years (Kawai et al. 2002: special thanks to Prof. Y. Watanabe for arrangement of co-work with National Research Institute of Fisheries Sciences). I proposed a cyclic-advantage hypothesis for species replacement of mackerel-sardine-anchovy cycle (Matsuda et al. 1992). If this hypothesis is true and overfishing of immature mackerel continues, both mackerel and sardine will not recover forever (Matsuda and Katsukawa 2002). I greately appreciate Japan Fisheries Agency's decision of TAC control on chub mackerel fishery, despite of a late decision.
2003．10.23 Census of Marine Life全体会議出席中のワシントンDCにて
昨夜のNHK衛星放送ニュースによると、いよいよ来年からサバ漁業の操業規制を実施するという。その規模については情報を得ていないが、私が水産庁にいた当時、Matsuda et al. (1992)でサバの乱獲が資源も漁獲量も減らしていると警告して以来（松田1995「共生とは何か」、2000「環境生態学序説」に紹介）、ようやく水産庁が操業規制を実施したことの意義は大きい。Kawai et al.( 2002)では1990年代の未成魚乱獲が資源回復を妨げたことを示した。これはH14年版の水産庁の資源評価にも記された。水産研究所並びに水産庁の担当者の粘り強い努力に敬意を表すると同時に、水産総合研究センターとの共同研究を斡旋して頂いた渡邊良朗教授に感謝する。先週のPICESでも1990年代のマサバ未成魚乱獲と日本のTAC（漁獲可能量）制度について質問があり、今後は資源回復を妨げるようなTACは設定されないだろうと返答したが、それが現実のものになった。
CoML会議に出席しているが、Smithsonian National Museum of Natural Historyで開かれたOcean Life: The known, unknown, and unknowableと題されたシンポでは、中心メンバーの一人であるR.Myers教授のマグロ90%減少説が成果として強調され、彼のサメ減少問題の講演の他に、Ian Poiner (CSIRO)およびBarbara Block（Stanford大）がマグロ問題を取り上げていた。今後マグロ延縄漁業に対する批判がさらに高まることが必至であり、おそらく、次のCITESではマグロ附属書掲載問題が討議されることだろう。Myers教授の解析はマグロ延縄漁業のデータから得られたものであり、漁業がなくなれば今後のデータは得られなくなる。他の資源監視手法を確立する必要があるが、もともとCPUE9割減（これはデータである）が資源の9割以上の減少を意味するという彼の主張には異論が多い（9割かどうかはともかく、大幅な資源減少を意味することは異論がない）。調査手法を変えるなら、今後はCPUEで比べられず資源量の比較になるのだから、資源量評価を合意しないといけない。
CoML会議では京大の白山義久教授を中心に進めているNaGISAという長期広域調査の成果が最も強調され、その次に深海の生物多様性についてもさまざまな研究成果が報告された。今後、深海（中深層）の生物資源を利用するにあたり、CoMLの研究成果は国際合意を作る上で見過ごすことができなくなるだろう。
Matsuda H, Kishida T, Kidachi T (1992) Optimal harvesting policy for chub mackerel in Japan under a fluctuating environment. Can J Fish Aq Sci 49:1796-1800
Temporal fluctuation in (he reproduction rates of chub mackerel (Scomber japonicus) was estimated for the period 1971-86, when stock abundance of chub mackerel varied from a high to low level. To estimate the effect of various harvesting policies on stock conservation and Ihe long-term catch, six harvesting policies were considered: (1) actual catch data during 1975-88, (2) 1/3 constant rate of exploitation, (3) low maximal catch amount, (4) 1/5 constant rate of exploitation, (5) prohibition of fishing when the stock is rare, and (6) constant-escapement policy. Using the data of reproduction rates during 1975-85, the final stock abundance at 1988 and the total catch amount during 1975-88 under each harvesting policy are calculated. We concluded that harvesting policies (4), (5), and (6) were effective for the stock conservation and that policies (2), (5), and (6) were effective for increasing the total catch.
On a eslime la fluctuation temporelle du taux de reproduction du maquereau blanc (Scomber Japonicus) pour la periode 1971-1986, pendant laquelle I'abondance du stock est passee d'un niveau eleve a un niveau bas. Pour estimer I'elfet des divcrses politiques de capture sur la conservation du stock et les prises a long terme, on a examine six politiques : 1) donnees reelles sur les captures de 1975 a 1988, 2) laux d'exploitation constant de 1/3, 3) prises maximales fixees au niveau le plus bas, 4) taux d'exploitation constant de 1/5, 5) interdiction de la peche en cas de rarete et 6) maintien d'un niveau constant des chappees. A partir des donnees sur les taux de reproduction do la p6riode 1975-85, on a calcule I'abondance du stock en 1988 et le montant total des captures de 1975 a 1988 en fonction de chacune des politiques. Nous concluons que les politiques 4, 5 et 6 sont efficaces en ce qui concerne la conservation du stock, et que les politiques 2, 5 et 6 sont efficaces en ce qui concerne ['augmentation du total des captures.
Kawai H, Yatsu A, Watanabe C, Mitani T, Katsukawa T, Matsuda H (2002) Recovery policy for chub mackerel stock using recruitment-per-spawning. Fish. Sci. 68:961-969.
ABSTRACT: The stock abundance of chub mackerel
(Scomber japonicus) in the Pacific Ocean off Japan declined
in the 1980s and remained at low levels through
the 1990s. There were recruitment successes
in 1992 and 1996. However, the cohorts born
in these years were heavily fished before
the age of maturity and chub mackerel has
not begun to recover. To investigate the
effects of conserving immature fish, we created
four recovery policies: (i) policy 0, actual
fishing mortality during the 1990s; (ii)
policy 1, conserve strong year classes; (iii)
policy 2, apply the average fishing mortality
in the 1970s1980s after 1992; and (iv) policy
3, a 55% reduction of the mortality adopted
by policy 2. Policy 3 was considered to be
the best in terms of final stock abundance
and total catch from 1992 to 1999. We also
calculate the future projection of stock
and catch under these three policies as well
as using average fishing mortality from 1993
to 1999. Using average fishing mortality
from 1993 to 1999, the stock will not be
recovered within the next 20 years. Even
under the best policy, the risk that the
final stock is not recovered to 3 million
tons within the next 10 years is 40%.
KEY WORDS: recovery probability, Scomber
japonicus, simulation model, spawning potential
ratio, virtual population analysis.
Matsuda H, Katsukawa T (2002) Fisheries Management Based on Ecosystem Dynamics and Feedback Control. Fisheries Oceanography 11 (6): 366-370
Recently, ecosystem management has become
popular for forestry, agriculture and fisheries
management. Carrying capacity and maximum
sustainable yield for a particular species
definitely depend on population sizes of
other species in the same ecosystem. Natural
stock fluctuations of sardine, anchovy and
chub mackerel are well known examples of
large, natural fluctuations. There is a negative
correlation among their fluctuations. In
accordance with the cyclic advantage hypothesis
for replacement of pelagic fish species (Matsuda
et al., 1992), we can predict the next dominant
species, despite an uncertainty in the year
of the next replacement. We recommend that
commercial fisheries should switch their
target to the next dominant species before
the stock of the present dominant species
collapses. Whilst total allowable catch (TAC)
of the present dominant species can be as
large as we can consume, TAC after the species
collapses should be much smaller than the
present catch level.
Key words: ecosystem management, species
replacement, target switching