Shifts in Japan’s Political Economy Regime Adjustments and changes.
ECOSYSTEM REGIME SHIFTS TRIGGERED BY OVERFISHING · 2011. 12. 21. · 21/12/2011 Ecosystem regime...
Transcript of ECOSYSTEM REGIME SHIFTS TRIGGERED BY OVERFISHING · 2011. 12. 21. · 21/12/2011 Ecosystem regime...
Ecosystem regime shifts triggered by overfishing21/12/2011 1
Christian MöllmannInstitute of Hydrobiology and Fisheries
Science, University of HamburgGermany
ECOSYSTEM REGIME SHIFTSTRIGGERED BY OVERFISHING
Ecosystem regime shifts triggered by overfishing21/12/2011 2
Background
• The general theme of this briefing note is the importance of overfishing in triggering ecosystem regime shifts !
• Ecosystem Regime Shifts are defined as infrequent and abrupt changes in ecosystem structure and function, occurring at multiple trophic levels and on large geographic scales !
Ecosystem regime shifts triggered by overfishing21/12/2011 3
This study ...• reviews prominent examples of ecosystem regime shifts; • discusses trophic cascades as the phenomenon by
which overfishing can cause ecosystem regime shifts;• reviews alternative stable state theory and evidence for
stable states in the reported cases of marine ecosystem regime shifts;
• presents conclusions on the causes of ecosystem regime shifts with special reference to overfishing;
• makes recommendations for future research and ecosystem-based management strategies.
Ecosystem regime shifts triggered by overfishing21/12/2011 4
Why are Ecosystem Regime Shifts of concern for management ? – Alternative Stable States Theory !
Ecosystem)state)
Pressure)
State)B)
State)A)
Ecosystem)state)
Pressure)
Ecosystem regime shifts triggered by overfishing21/12/2011 5
Review of Ecosystem Regime Shifts
1"
2"
3"4"
5"
1 – North Pacific, 2 – Eastern Scotian Shelf, 3 – North Sea, 4 – Baltic Sea, 5 – Black Sea.
Ecosystem regime shifts triggered by overfishing21/12/2011 6
Selection of studies
• covered all trophic levels, i.e. phyto- and zooplankton, meso-predatory and top-predatory fish
• used multivariate methods (e.g. Principal Component Analysis – PCA – to summarize and integrate the changes into a few variables
• used a regime shift detection method• for Northern Pacific, Eastern Scotian Shelf, North Sea
and Baltic Sea• exception Black Sea, where changes over several
trophic levels are reported separately
Ecosystem regime shifts triggered by overfishing21/12/2011 7
Example of Ecosystem Regime Shift – the North Pacific (Hare and Mantua, 2000)
a)
Year1965 1970 1975 1980 1985 1990 1995
Ecos
yste
mSt
ate
(PC
1&
PC2)
-2
-1
0
1
2
PC1-2 -1 0 1 2
PC
2
-2
-1
0
1
2
65
66 6768
69
70
7172
737475
76
77
78
79 80
81
82
8384
8586
87
88
8990
91
92
93
9495
96
97
b)
Ecosystem regime shifts triggered by overfishing21/12/2011 8
Comparison of Regime Shift timing –common climate driver ?
Ecosystem regime shifts triggered by overfishing21/12/2011 9
Comparison of Regime Shift timing –common climate driver ?
Ecosystem regime shifts triggered by overfishing21/12/2011 10
Review of Ecosystem Regime ShiftsECOSYSTEM STUDY TIMING MAIN DRIVER
North Pacific Hare and Mantua, 2000 1977 and 1989 Climate
Eastern Scotian Shelf Choi et al., 2005 1976 and 1990Climate,
overfishing
North Sea
Beaugrand, 20041982-88; two periods:1982-85 and 1988/89
Climate
Weijerman et al., 2005 1979 and 1988 Climate
Kenny et al., 2009 1993 Climate, overfishing
Baltic Sea Möllmann et al., 2009 1988-93Climate,
overfishing,eutrophication
The Sound Lindegren et al., 2010a 1987/88 Climate
Black Sea Oguz and Gilbert, 2007 1973/4 and 1989 Overfishing, species invasion
Ecosystem regime shifts triggered by overfishing21/12/2011 11
Fishing as a driver – Trophic Cascades
Phytoplankton
Zooplankton
Planktivores
Piscivores
Ecosystem regime shifts triggered by overfishing21/12/2011 12
Review of trophic cascadesECOSYSTEM STUDY SPECIES/TROPHIC LEVELS
INVOLVED
Eastern Scotian Shelf Frank et al. 2005Demersal fish, pelagic forage fish, large
crustaceens, large zooplankton,phytoplankton
Baltic SeaCasini et al., 2008, Casini et al., 2009 ; Möllmann et al., 2008
Cod, sprat, zooplankton, phytoplankton
Black SeaDaskalov et al., 2007; Oguz andGilbert, 2007
Pelagic predatory fish, smallplanktivorous fish, gelatinous plankton,
zooplankton, phytoplankton
Trophic cascade at the Eastern Scotian Shelf (from Scheffer et al., 2005, after Frank et al., 2005)
Ecosystem regime shifts triggered by overfishing21/12/2011 13
Drivers of Ecosystem Regime Shifts
• Climate (atmospheric forcing)• (Over-) Fishing• Eutrophication• Species invasion („jellification“)
Ecosystem regime shifts triggered by overfishing21/12/2011 14
How do multiple drivers interact ? – Resilience !
Resilient ecosystem – deep basin of attraction !•External driver (black arrows) cannot change the ecosystem into a new state!
Degraded ecosystem – shallow basin of attraction !•External driver 1 (e.g. FISHING) has degraded the ecosystem•External driver 2 (e.g. CLIMATE -black arrows) can change the ecosystem into a new state!
Ecosystem regime shifts triggered by overfishing21/12/2011 15
Positive feedbacks lead to Alternative Stable States !
Top-Pre-dator
Meso-predator
Decreased predation !
Increased predationon fish eggs and larvae !
Ecosystem regime shifts triggered by overfishing21/12/2011 16
How to avoid unwanted ecosystem regime shifts –early warning systems !
Time series of spatial variance as an early warning indicator and mean ecosystem state in Pavlof Bay and Eastern Scotian Shelf (Litzow and Ciannelli, 2008)
Critical slowing down as an early warning indicator – increase in lag-1 autocorrelation in climate dynamics; the period preceding thetransition from a greenhouse state to an icehouse state on the Earth 34 Myrago (Scheffer et al., 2009)
Ecosystem regime shifts triggered by overfishing21/12/2011 17
Key findings• The synchronicity in timing of ecosystem regime shifts over the Northern
hemisphere during the late 1980s/early 1990s suggests a common climate driver.
• Trophic cascades triggered by overfishing are regularly observed, indicating that multiple external drivers are usually needed to cause ecosystem regime shifts.
• Multiple external drivers interact in a way that one undermines resilience (e.g. fishing) and another one (e.g. abrupt climate change) gives the final impulse for an ecosystem regime shift.
• Ecosystem regime shifts can be difficult to reverse when alternative stable states are involved. Indications for the latter exist from multiple ecosystems.
• Ecosystem-based management strategies are needed to avoid ecosystem regime shifts and early warning systems need to be developed.