Zooplankton volume trends off Peru between 1964 and 2001

Abstract

Abstract Zooplankton samples were collected by Hensen net (300 μm) vertical hauls from a depth of 50 m in 57 surveys along the Peruvian coast during winter and summer from 1961 to 2001. In general, the latitudinal distribution of total zooplankton volumes showed highest values within 60 nmi (111 km) of the coast. Predominantly during the 1960s, high zooplankton volumes were found between 4°S–6°S and 14°S–16°S, coinciding with narrow continental shelf areas. Strong declines of zooplankton volumes were observed in these regions in the 1990s. In the long term, zooplankton volumes off Peru were higher during “cold” decades, particularly in the 1960s, than during “warm” decades. This research supports the regime-shift previously observed in the Peruvian coastal upwelling, and is in agreement with global changes observed in lower and upper trophic levels elsewhere in the Pacific and North Atlantic basins.