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Comparison of Synchronous Ecological Regime Shifts in the Humboldt and Kuroshio Currents

Comparison of Synchronous Ecological Regime Shifts in the Humboldt and Kuroshio Currents Jürgen Alheit Baltic Sea Research Institute Warnemünde, Germany. Anomalies of Hemispheric Air Temperature. °C. Month. Interdecadal time series at 23.5°S c) Z b : thin line - reconstructed thermocline

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Comparison of Synchronous Ecological Regime Shifts in the Humboldt and Kuroshio Currents

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  1. Comparison of Synchronous Ecological Regime Shifts in the Humboldt and Kuroshio Currents Jürgen Alheit Baltic Sea Research Institute Warnemünde, Germany

  2. Anomalies of Hemispheric Air Temperature °C Month

  3. Interdecadal time series at 23.5°S c) Zb: thin line - reconstructed thermocline (Pizarro and Montecinos, Geophys. Res. Lett., 2004)

  4. ENSO 72/73 ENSO 82/83 ENSO 97/98

  5. Peruvian Phytoplankton Volumes 1976 - 1999 Northern Peru 0 – 30 miles Central Peru 30 – 60 miles Southern Peru > 60 miles Peruvian Zooplankton Volumes 1964 - 1988

  6. Dynamics of Anchovies, Sardines, and Zooplankton Anchovy Zooplankton Sardine

  7. other Pelagics Anchovy Plankton decrease of Peruvian zooplankton after 68 biomass decrease 69-71 increased sardine spawning since 69 decrease of Chilean zooplankton after 69 increased relative abundance of sardine and horse mackerel since 70 surplus production rate turns negative after 68 shift in relative abundance of larvae of non-fished mesopelagic species after 69 recruitment collapse 71 Observed Biological Changes in Humboldt Current 1968-71 Regime Shift Alheit and Niquen 2004 Progr. Oceanogr. 60

  8. density-dependent processes increased predation due to increased overlap with oceanic predators changes in prey fields increased cannibalism of eggs and larvae increased predation on eggs and larvae reduction of large copepods (anchovy food) increased predation on juveniles and adults by mackerel and horse mackerel increase of smaller copepods (sardine food) increased catchability Mechanisms of Regime Shifts in Humboldt Current – Causal Relationships slackening of trades reduced upwelling, deepening of thermocline, productivity changes advection of warm subtropical oceanic water to coast reduction of cool anchovy habitat negative impacts on trophodynamics of anchovy

  9. Shift anchovy-sardine Peru: 1968-1970 Shift thermocline shallow-deep Peru: 1968-1970 Shift anchovy-sardine Japan: 1966-1972 Shift MLD shallow-deep Kuroshio: mid-1960s ____________________________________________________ Shift sardine-anchovy Peru: mid-1980s Shift thermocline deep-shallow Peru 1982-1983 Shift sardine-anchovy Japan: mid-late 1980s Shift MLD deep-shallow Kuroshio: 1985 Dynamics of mixed layer depth Kuroshio (Yasuda et al., 2000, Prog. Oceanogr. 47)

  10. Major Question: What drives teleconnection between Humboldt and Kuroshio systems? Conclusions Decadal-scale climate variability drives regime shifts of anchovy and sardine populations in HC and KC  teleconnection ? Turning points in dynamics of small pelagics correspond to changes in sub- surface processes (late 1960s-1970; mid-1980s) No strong signals of climate regime shift in mid-70s in dynamics of HC and KC small pelagics HC anchovy collapse caused by combination of regime shift and overfishing Single El Niño events are only short-term perturbations for HC anchovy

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