Comparison of Synchronous Ecological Regime Shifts in

the Humboldt and Kuroshio Currents

Jürgen Alheit

Baltic Sea Research Institute Warnemünde, Germany

Geography of sardine populations

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Catch Records of Japanese and Peru-Chile sardine populations

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California sardine

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Catch Records of Japanese and California sardine populations

Synchronies in catch records (hard data but mixes fishing with environment)

Anomalies of Hemispheric Air TemperatureM

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

Anchovy and Sardine Catches in Humboldt Current

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ENSO 82/83

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Peruvian Zooplankton Volumes 1964 - 1988

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Peruvian Phytoplankton Volumes 1976 - 1999

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Per

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Anchovy

SardineZooplankton

Dynamics of Anchovies, Sardines, and Zooplankton

Observed Biological Changes in Humboldt Current 1968-71

Regime Shift

Plankton

decrease of Peruvianzooplankton after 68

decrease of Chileanzooplankton after 69

shift in relative abundance of larvae of non-fishedmesopelagic species after 69

Anchovy

biomass decrease 69-71

surplus productionrate turns negative after 68

recruitment collapse 71

other Pelagics

increased sardinespawning since 69

increased relativeabundance of sardine and horse mackerel since 70

Alheit and Niquen 2004Progr. Oceanogr. 60

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

changes in prey fields

reduction of large copepods (anchovy food)

increase of smaller copepods (sardine food)

increased predation due to increased overlap with oceanic predators

increased predation on eggs and larvae

increased predation on juveniles and adults by mackerel and horse mackerel

increased cannibalism of eggs and larvae

increased catchability

density-dependent processes

Normalized Japanese Catches

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Normalized Sardine Catches

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Kuroshio

Normalized Anchovy Catches

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Humboldt

Kuroshio

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)

Conclusions

Decadal-scale climate variability drives regime shifts of anchovy andsardine 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 andKC 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

Major Question:

What drives teleconnection between Humboldt and Kuroshio systems?