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 Month °C

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

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

Northern Peru Central Peru Southern Peru Peruvian Zooplankton Volumes – 30 miles 30 – 60 miles > 60 miles Peruvian Phytoplankton Volumes

Anchovy Sardine Zooplankton Dynamics of Anchovies, Sardines, and Zooplankton

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

Shift anchovy-sardine Peru: Shift thermocline shallow-deep Peru: Shift anchovy-sardine Japan: Shift MLD shallow-deep Kuroshio: mid-1960s ____________________________________________________ Shift sardine-anchovy Peru:mid-1980s Shift thermocline deep-shallow Peru 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 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 Major Question: What drives teleconnection between Humboldt and Kuroshio systems?