Seek simplicity, but distrust it

クジラ類とその餌生物である
魚類との関係
• 松田裕之(横浜国立大学）
10/20/04
http://risk.kan.ynu.ac.jp/matsuda/2004/041114f.ppt
1
http://risk.kan.ynu.ac.jp/matsuda/2004/041114f.ppt
Overview
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•
•
•
•
鯨害獣論
上位捕食者激減説
生態系モデル
We can get more fish
単純さを求めよ．しかし，それを信じるな
10/20/04
2
鯨類の摂食量と漁獲量
10/20/04
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鯨類の初期資源量と現在
10/20/04
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鯨類乱獲の歴史
南氷洋における鯨類の捕獲量の推移
捕獲頭数
50000
40000
30000
20000
マッコウ
ナガス
10000
ニタリ
シロナガス
ザトウ
0
1931/32
10/20/04
Ref:
41/42
51/52
61/62
71/72
年
ミンク
81/82
91/92
森光代作図 5
謬説：クジラ害獣論
•
•
•
•
Fallacy of whale-fishery competition as
reason for culling whales
鯨はカタクチイワシ、中深層性ハダカイワ
シなどを大量に摂食
必ずしも漁業とは競合しない
大昔より鯨類全体としては減っている
たくさんいるミンク鯨
を食べよう！
資料：日本鯨類研究所
10/20/04
file: Institute for Cetacean Research
6
http://risk.kan.ynu.ac.jp/matsuda/2004/041114f.ppt
Overview
•
•
•
•
•
鯨害獣論
上位捕食者激減説
生態系モデル
We can get more fish
単純さを求めよ．しかし，それを信じるな
10/20/04
7
Whales Before Whaling in the North Atlantic
• DNA多様性
解析：大西洋
の鯨類は商業
捕鯨以前より
ずっと少ない
（差＞累積捕
獲数）
10/20/04
Population abundance (thousands)
Roman J & Palumbi SR (2003) Science 301:508-510
Historical
Current
600
300
Humpback
Fin
Minke
8
日本のマイ
ワシ減少
期？
ペルーカタクチイワシ豊漁期
Fishing Down!漁業下落
mean trophic level
Pauly et al. (左Science1998:279:860; 右2002 Nature 418:669)
Marine areas
?
inland areas
Fig. 1. Global trends of mean trophic level of fisheries landings, 1950 to 1994
(左),
1970
to 1997（右）
10/20/04
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大型魚類の生物体量97-99%減少説
(Jennings & Blanchard 2004 J Anim Ecol
73:632)
• We propose a method, based on
macroecological theory, to predict
the abundance and size-structure of
an unexploited fish community
from a theoretical abundance–body
mass relationship (size spectrum).
• We suggest that the current biomass
of large fishes weighing 4–16 kg
and 16–66 kg, respectively, is
97·4% and 99·2% lower than in the
absence of fisheries exploitation.
The results suggest that depletion
of large fishes due to fisheries
exploitation exceeds that described
in many short-term studies.
10/20/04
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Marine Ecosystems Concerns
海洋生態系への懸念
R. A. Myers & B. Worm (2002)
Nature in press. “Rapid worldwide
deple-tion of large predatory fish
communities” …We conclude that
declines of large predators that initially
occurred in coastal regions, have
extended throughout the global ocean,
with potentially large consequences on
ecosystems.
Top predators are good indicator of
ecosystems.
10/20/04
11
Nature Myers論文への国際的
なマグロ研究者の反論
• John Hampton, John R. Sibert, and Pierre
Kleiber Effect of longlining on pelagic fish
stocks - tuna scientists reject conclusions of
Nature article
http://www.spc.int/OceanFish/Docs/Researc
h/Myers_comments.htm
10/20/04
12
http://risk.kan.ynu.ac.jp/matsuda/2004/041114f.ppt
Overview
•
•
•
•
•
鯨害獣論
上位捕食者激減説
生態系モデル
We can get more fish
単純さを求めよ．しかし，それを信じるな
10/20/04
13
Catch of demersal marine fish has
not grow since 1970s （FAO1996)
10/20/04
http://www.fao.org/WAICENT/FAOINFO/FISHERY/publ/sofia/fig5e.asp
14
Catch of pelagic fish has still been
increasing
anchoveta
sardine
Atlantic herring
10/20/04
chub
mackerel
http://www.fao.org/WAICENT/FAOINFO/FISHERY/publ/sofia/fig4e.asp
15
http://risk.kan.ynu.ac.jp/matsuda/2004/041114f.ppt
Overview
•
•
•
•
•
鯨害獣論
上位捕食者激減説
生態系モデル
We can get more fish
単純さを求めよ．しかし，それを信じるな
10/20/04
16
オットセイ駆除は、メルルーサを減らす可
ベンゲラ海域生態系の食物網
能性の方が高いだろう（Yodzis
1998)
（Yodzis
1998, 宮下・野田『群集生態学』2003）
鳥
ｵｯﾄｾｲ
鯨類
鮫
鮪
ﾒﾙﾙｰｻ
鯵
鯖
片口鰯
細菌
10/20/04
浮植浮小動分解者
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群集生態学の最も重要な知見と
は？
• Indeterminacy in indirect effects of
community interactions (Yodzis 1988);
• From sensitivity analysis, the total
effect between species is positive or
negative even though process errors
exist in growth rate;
• The “vulnerability” is not common
for all species, and changes with
conditions (evolutionary ecology).
10/20/04
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5
4
3
1
2
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“...in a complicated food web structure, indirect
Twoofphenotypes
whales-fisheries
effects
culling topof predator
(whales) on
abundance of competition
target fish isidea
either positive or
negative,...” By Yodzis 2001 Trend Ecol Evol
Whales destroy
the ocean.
Fisheries destroy
the ocean.
By Japan Gov.
10/20/04
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, aisclassic
this illusion?
Wasp-waist is
dream...
birds
seals
sardine/anchovy
tunas
lantern fish
pelagic
copepods
krill
deep sea
....
Only 5 to 10 percent of
us succeed of the weightloss industry
• Anyway, we need to investigate how to fluctuate the
total biomass of small pelagics.
10/20/04
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I still recommend eating small
pelagics
• Catch of small pelagics is still much smaller
than consumption by top predators.
• Total biomass of top predators decreased in
the 20th century.
• Some species when it is rare is overfished.
• Eating small pelagics is definitely smaller
impact on eating higher trophic levels.
10/20/04
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http://risk.kan.ynu.ac.jp/matsuda/2004/041020p.ppt
Species replacement among pelagic fishes
10/20/04
22
updated
after Matsuda & Katsukawa (2002 Fish Oceanogr 11:366)
Cyclic Advantage Hypothesis for
“sardine-anchovy-chub mackerel cycles”
The next dominant is
anchovy –
The second next is
chub mackerel
sardine
mackrel
Anchovy, Pacific
saury, jack mackerel
Matsuda et al. (1992) Res. Pop.
Ecol. 34:309-319
10/20/04
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Possible combination between
regime shift and species interactions
• When sardine increased, water temperature
differed between off Japan and off
California (McFarlane et al. 2002).
• A possible answer: “Temperature does not
solely determine the sardine's stock
dynamics.”
• Climate change is a trigger for species
replacement (Matsuda et al. 1992).
10/20/04
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Global regime shift drives synchronicity
• We consider a cyclic-advantage model:
Nij’ = c+Ni exp[rij(t)–ai1Ni1–ai2Ni2–ai3Ni3]
• for species i (=1,2,3) in region j (=1,2);
• rij(t) positively correlates between
species (i) and between regions (j).
• sr: inter-regional correlation in rij(t).
10/20/04
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Simulated effect of “regime shift” sr
& correlation between species ss
small sr
• If sr is small, no synchronicity;
sardine increased off Japan and
sardine/anchovy increased off California
independently.
intermediate sr and large sr
large sr and ss
10/20/04
• If sr & ss are large, sardine
increased off Japan almost when
some species increased off
California (incomplete
synchronicity);
• If sr is large and ss is small, sardine
increased both off Japan and
California simultaneously.
• Which is true?
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Sardine-anchovy-mackerel cycle
hypothesis ...
• is falsifiable because the next dominant
is predictable.
• encourages multiple species
management (target-switching; Katsukawa &
Matsuda 2003 Fish Res 60:515)
• does not predict when the next
replacement occurs (depending probably
on regime shift...)
10/20/04
27
http://risk.kan.ynu.ac.jp/matsuda/2004/041114f.ppt
Overview
•
•
•
•
•
鯨害獣論
上位捕食者激減説
生態系モデル
We can get more fish
単純さを求めよ．しかし，それを信じるな
10/20/04
28
Seek simplicity, but distrust it
–Begon, Harper & Townsend (1986) "Ecology:
Individuals, Populations and Communities“
反対の立場：
• Seek complexity, and trust it.
Include all factors and data into the model
There are two types of models:
• Eye-opening (“目からうろこを落とす”)
• Mystifying (“人を煙に巻く”)
10/20/04
29
http://risk.kan.ynu.ac.jp/matsuda/2004/041020.ppt
Seek simplicity, but distrust it
• 必要最低限の要因を考慮した数理モデル
を考える
• 観測誤差と過程誤差を考慮する
• Simple model with errors は反証可能（よ
く考えてみれば成り立たないシナリオ，前
提だけを排除する）
10/20/04
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What is target-switching in fisheries?
• Fishery that focuses its effort (fi) on a
temporally abundant species or stock i.
fj  Bi / SBj.
•It saves rare stock, increases total catch.
Constant Harvest Ratio
7
1 10
6
4 10
Yield
Biomass
6
Positive Switching
6
8 10
8 10
6
6
3 10
3 10
6
6
6 10
6 10
6
6
2 10
6
4 10
2 10
6
4 10
6
6
1 10 6
2 10
1 10 6
2 10
20
20
10/20/04
7
1 10
6
4 10
40
40
60
60
80
80
100
100
20
20
40
40
60
60
Katsukawa & Matsuda (2003 Fish. Res)
80
80
100
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「単純で誤差を含むモデル」SMｗE
の利点
SMwE
•
•
•
•
•
Complex models
合理的な結果ならば直感的 • 直感的に説明しにくい
に説明しやすい
モデルの自由度（細工の余 • 多くのパラメタの値を
地）が少ない
最尤法などで推定
非現実的な前提だけを排除 • 過去のデータを過適
する
合overfitting
多様な前提や予想を受け入
れる
• 将来を一意的に予想
リスク分析に有効である
する
10/20/04
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未知のことと不可知のことを弁
える（KUU, CoML’s slogan)
•
•
•
•
•
Seek a falsifiable
testable hypothesis;
Avoid type II
I errors (orthodox
science)
(precautionary
principle)
Predict
likely future
future
Certify “maximum”
what is unlikely
Expect
case
Preparean
theoptimistic
worst case
(risk management)
Design
to test hypotheses in
Give upmanagement
testing hypothesis;
the future
(adaptive management)
10/20/04
Census of Marine Life: http://www.nagisa.coml.org/
33
Recommendations #1
1. Do fishing down in food items!!
•
Eat small pelagic fishes
2. Eat more fish, not use as fish meal!!
•
Feed cows on grass, not corns (“Beyond Beef”)
3. Reduce discards before and after landings
(our dishes);
4. Establish food market of temporally
fluctuating pelagic fishes
10/20/04
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Recommendations #2
5. Switch a target fish (species replacement)
6. Conserve immatures
•
& Save a chance of multiple reproduction
7. Monitor “ecosystems” (not only target)
8. Improve technology for selective fishing
9. Conserve both fishes and fisheries;
•
10/20/04
unsustainable agriculture and forestry are
problems rather than small pelagic fisheries
35

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