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10/20/04 1
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）
http://risk.kan.ynu.ac.jp/matsuda/2004/041114f.ppt
10/20/04 2
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
http://risk.kan.ynu.ac.jp/matsuda/2004/041114f.ppt
10/20/04 3
鯨類の摂食量と漁獲量
10/20/04 4
鯨類の初期資源量と現在
10/20/04 5
鯨類乱獲の歴史南氷洋における鯨類の捕獲量の推移
Ref: http://luna.pos.to/whales/sta.html
シロナガス
ナガス
ザトウ
ニタリ
ミンク
マッコウ
0
10000
20000
30000
40000
50000
1931/32 41/42 51/52 61/62 71/72 81/82 91/92
年
捕獲頭数
森光代作図
10/20/04 6
謬説：クジラ害獣論Fallacy of whale-fishery competition as reaso
n 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file: Institute for Cetacean Research
10/20/04 7
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
http://risk.kan.ynu.ac.jp/matsuda/2004/041114f.ppt
10/20/04 8
Whales Before Whaling in the North Atlantic Roman J & Palumbi SR (2003) Science 301:508-510
• 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）
Historical
Current
Humpback Fin Minke
300
600
Pop
ula
tion
ab
un
dan
ce (
thou
san
ds)
10/20/04 9
Fig. 1. Global trends of mean trophic level of fisheries landings, 1950 to 1994 ( 左 ),
1970 to 1997 （右）
Fishing Down! 漁業下落Pauly et al. ( 左 Science1998:279:860; 右 2002 Nature 418:669)
Marine areas
inland areas
ペルーカタクチイワシ豊漁期日本のマイワシ減少
期？
?
mean
tro
ph
ic level
10/20/04 10
大型魚類の生物体量 97-99% 減少説(Jennings & Blanchard 2004 J Anim Ecol 73:63
2)• We propose a method, based on ma
croecological 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 11
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 12
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 articlehttp://www.spc.int/OceanFish/Docs/Research/Myers_comments.htm
10/20/04 13
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
http://risk.kan.ynu.ac.jp/matsuda/2004/041114f.ppt
10/20/04 14
Catch of demersal marine fish has not grow since 1970s （ FAO1996)
http://www.fao.org/WAICENT/FAOINFO/FISHERY/publ/sofia/fig5e.asp
10/20/04 15
Catch of pelagic fish has still been increasing
http://www.fao.org/WAICENT/FAOINFO/FISHERY/publ/sofia/fig4e.asp
anchoveta
sardine
chub mackerelAtlantic herring
10/20/04 16
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
http://risk.kan.ynu.ac.jp/matsuda/2004/041114f.ppt
10/20/04 17
ベンゲラ海域生態系の食物網（ Yodzis 1998, 宮下・野田『群集生態学』 200
3 ）ｵｯﾄｾｲ
ﾒﾙﾙｰｻ
鳥鯨類
鮪鮫
鯵片口鰯
鯖
細菌 浮植 浮小動 分解者
オットセイ駆除は、メルルーサを減らす可能性の方が高いだろう（ Yodzis 19
98)
10/20/04 18
群集生態学の最も重要な知見とは？
• Indeterminacy in indirect effects of community interactions (Yodzis 1988);
1 2
3
5
6
4
• The “vulnerability” is not common for all species, and changes with conditions (evolutionary ecology).
• From sensitivity analysis, the total effect between species is positive or negative even though process errors exist in growth rate;
10/20/04 19
Two phenotypes of whales-fisheries competition idea
By Japan Gov.
Whales destroyWhales destroythe ocean.the ocean.
“...in a complicated food web structure, indirect effects of culling top predator (whales) on abundance of target fish is either positive or negative,...” By Yodzis 2001 Trend Ecol Evol
Fisheries destroyFisheries destroythe ocean.the ocean.
10/20/04 20
Wasp-waist is a classic dream...
• Anyway, we need to investigate how to fluctuate the total biomass of small pelagics.
birds seals tunas
copepods krill ....
, is this illusion?
pelagic
sardine/anchovy lantern fish
deep sea
Only 5 to 10 percent of us succeed of the weight-loss industry
10/20/04 21
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 22
Species replacement among pelagic fishes
http://risk.kan.ynu.ac.jp/matsuda/2004/041020p.ppt
updated after Matsuda & Katsukawa (2002 Fish Oceanogr 11:366)
10/20/04 23
Cyclic Advantage Hypothesis for “sardine-anchovy-chub mackerel cycles”The next dominant is
anchovy –The second next is
chub mackerel
Anchovy, Pacific saury, jack mackerel
mackrelsardine
Matsuda et al. (1992) Res. Pop. Ecol. 34:309-319
10/20/04 24
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 25
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 spec
ies (i) and between regions (j).
• r: inter-regional correlation in rij(t).
10/20/04 26
Simulated effect of “regime shift” r & correlation between species s
• If r is small, no synchronicity; sardine increased off Japan and sardine/anchovy increased off California independently.
• If r & s are large, sardine increased off Japan almost when some species increased off California (incomplete synchronicity);
• If r is large and s is small, sardine increased both off Japan and California simultaneously.
• Which is true?
small r
large r and s
intermediate r and large r
10/20/04 27
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 28
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
http://risk.kan.ynu.ac.jp/matsuda/2004/041114f.ppt
10/20/04 29
Seek simplicity, but distrust it
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” )
–Begon, Harper & Townsend (1986) "Ecology: Individuals, Populations and Communities“
10/20/04 30
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）
http://risk.kan.ynu.ac.jp/matsuda/2004/041020.ppt
10/20/04 31
What is target-switching in fisheries?
• Fishery that focuses its effort (fi) on a temporally abundant species or stock i.fj Bi / Bj.
Bio
mas
s
20 40 60 80 100
2106
4106
6106
8106
1107
20 40 60 80 100
2106
4106
6106
8106
1107
•It saves rare stock,
Constant Harvest Ratio Positive Switching
Y
ield
20 40 60 80 100
1106
2106
3106
4106
20 40 60 80 100
1106
2106
3106
4106
increases total catch.
Katsukawa & Matsuda (2003 Fish. Res)
10/20/04 32
「単純で誤差を含むモデル」 SMｗE
の利点SMwE • 合理的な結果ならば直感的
に説明しやすい• モデルの自由度（細工の余地）が少ない
• 非現実的な前提だけを排除する
• 多様な前提や予想を受け入れる
• リスク分析に有効である
Complex models• 直感的に説明しにく
い• 多くのパラメタの値
を最尤法などで推定• 過去のデータを過適
合 overfitting• 将来を一意的に予想
する
10/20/04 33
未知のことと不可知のことを弁える（ KUU, CoML’s slogan)• Seek a testable hypothesis;
• Avoid type I errors (orthodox science)
• Predict “maximum” likely future
• Expect an optimistic case
• Give up testing hypothesis;
falsifiable
II errors (precautionary principle)
Certify what is unlikely future
Design management to test hypotheses in the future (adaptive management)
Census of Marine Life: http://www.nagisa.coml.org/
Prepare the worst case (risk management)
10/20/04 34
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 35
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 fishing9. Conserve both fishes and fisheries;
• unsustainable agriculture and forestry are problems rather than small pelagic fisheries
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