INTERANNUAL VARIATION OF ICHTHYOPLANKTON COMPOSITION 

 AND ABUNDANCE RELATIONS OFF NORTHERN CHILE, 1964-83 



VaLKRIK J LOEB' AND OMAR ROJAS^ 



ABSTRACT 



Larval fishes were collected off of northern Chile during winter (July-September) ichthyoplankton 

 surveys undertaken in 1964-70, 1972-73, and 1983. The 19-year timespan included a wide variety 

 of hydrographic conditions in the Humboldt Current area (cold years. El Nino events, and intervening 

 transition years); it also included the decline and collapse of the anchoveta fisheries and increases of 

 sardine, mackerel, and jack mackerel stocks off northern Chile and Peru. The ichthyoplankton data 

 are examined in relation to ambient hydrographic conditions as well as to possible chronological 

 changes in environmental conditions which led to the increased Chilean sardine stocks and anchoveta 

 fishery collapse. 



More coherent patterns come from considerations of larval fish species composition in 1964-69 and 

 1970-73 data sets than from years of "similar" hydrographic conditions. A marked shift in relative 

 abundances of nonfished mesopelagic species in 1969-70 is associated with changes within long-term 

 physical data bases from Chile and Peru suggesting a large-scale environmental change. Sardine 

 stock growth began with successful larval survival of 1968-69 and later year classes. Anchoveta stock 

 decline began in 1972 probably due to poor larval survival. Affiliation of anchoveta and coastal 

 species larval abundance implies that they are similarly influenced by coastal processes. An atmos- 

 pherically driven oceanic circulation change beginning in the late 1960's and possibly involving 

 onshore presence of subtropical and or oceanic waters and altered coastal processes may have been 

 responsible for the changes in the northern Chilean fish assemblages. 



The Humboldt Current region, like the other 

 major eastern boundary current systems (Califor- 

 nia, Benguela, and Canary Currents) is domi- 

 nated by pelagic schooling fish stocks including 

 anchoveta (Engraulis), sardine iSardinops), 

 hake iMerluccius), mackerel (Scomber), jack 

 mackerel (Trachurus), and bonita iSarda) (Par- 

 rish et al. 1983). These fish stocks, like those in 

 the other eastern boundary current areas, exhibit 

 extreme population fiuctuations. Most notable in 

 the past 30 years are the collapses of Peruvian 

 and Chilean anchoveta stocks in the mid-1970's 

 and their succession by sardine and, to a lesser 

 extent, mackerel and jack mackerel stocks (San- 

 tander and Flores 1983; Serra 1983). 



Hydrographic complexity and variability are 

 characteristic of eastern boundary current sys- 

 tems. Included in the Humboldt Current region 

 are equatorial, subequatorial, subantarctic, and 

 antarctic oceanic water masses; northward flow- 

 ing currents and opposing countercurrents; and 

 wind driven, seasonally variable coastal up- 

 welling (Wyrtki 1967). Additionally, the region is 



iMoss Landing Marine Laboratories, P.O. Box 450, Moss 

 Landing, CA 95039. 



2Instituto de Fomento Pesquero, Avenida Pedro de Valdivia 

 2633, Casilla 1287, Santiago, Chile. 



subject to 1) large seasonal and longer period 

 fluctuations in advection of water masses of 

 markedly different properties and 2) large in- 

 terannual differences in the timing and intensity 

 of seasonal upwelling processes (Bakun 1987; 

 Bernal et al. 1983; Parrish et al. 1983; Robles et 

 al. 1976). The clearest and generally considered 

 most important of the nonseasonal processes in- 

 fluencing the biology of the current system is the 

 El Nino phenomenon (Bernal et al. 1983; Guillen 

 1983). El Nino events off Peru and Chile are 

 marked by large-scale atmospherically driven 

 southward and coastward advection of warm, 

 high-salinity equatorial and subequatorial sur- 

 face waters, weakening of coastal upwelling (or 

 upwelling of warm nutrient-poor waters), and 

 weakening of subsequent phytoplankton blooms. 

 These El Nino or warm-water periods are vari- 

 able in their intensity and duration (Guillen 

 1983; Santander and Flores 1983). In contrast to 

 these periods are more "normal" cold-water 

 events resulting from atmospherically driven in- 

 tensification of northward flowing cold, low- 

 salinity subantarctic waters and seasonal up- 

 welling of cold, nutrient-rich water. Major El 

 Nino events occurred in 1891, 1925-26, 1940-41, 

 1957-58, 1965, 1972-73, 1976, and 1982-83; 



Manu.script accepted September 1987. 

 FISHERY BULLETIN: VOL. 86, NO. 1, 1988. 



