Japan Fisheries Agency regulates 2004 total allowable catch (TAC) of Pacific chub mackerel

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。


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