FISHERY BULLETIN: VOL. 69, NO. 4 



phytoplankton stock in a patch of upwelled water 

 they observed continuously for 5 days in April 

 1966, south of Callao. Both zooplankton and the 

 anchovy must be considered as potentially impor- 

 tant direct grazers of the phytoplankton. Rojas 

 de Mendiola et al. (1969) found the stomach con- 

 tents of anchovies collected in February-March 

 of 1968 in the area of this study (i.e., off Supe) 

 to be predominantly phytoplankton whereas 

 those from the south (Tambo de Mora) were 

 mainly zooplankton remains. At that time 

 the phytoplankton crop off Supe was princi- 

 pally diatoms while diatoms were of much 

 less importance in the phytoplankton popula- 

 tions off Tambo de Mora. Rojas de Mendiola 

 et al. (1969) also reported they had some evi- 

 dence that adult anchovies may prefer phyto- 

 plankton while animal plankters are the choice 

 of juveniles (65-70 mm anchoveta). 



In May-June of 1969 the Food Chain Research 

 Group of the Institute of Marine Resources, Uni- 

 versity of California, in cooperation with the 

 Instituto del Mar del Peru studied various as- 

 pects of the physical processes and biological 

 populations associated with upwelling along the 

 Peruvian coast during austral fall. This work 

 was carried out as Leg 7 of the PIQUERO Cruise 

 of the RV Thomas Washington. A complete 

 description of these studies is recorded in two 

 "unpublished" data records on file with the Uni- 

 versity of California, Institute of Marine Re- 

 sources (1970,° 1971'). From these studies the 

 coastal current system along Peru was also de- 

 scribed (Stevenson, 1971). During PIQUERO 

 Leg 8 the work was extended north to the 

 Equator where the zonal circulation was studied 

 (Stevenson and Taft, 1971). Anchovy studies 

 (abundance, schooling, stomach contents, etc.) 

 were carried out by Villanueva, Jordan, and 



' University of California, Institute of Marine Re- 

 sources. 1970. Research on the marine food chain; 

 progress report, July 1969 - June 1970. Part III. Data 

 record. Cruise PIQUERO, Leg 7. Section 1. Physical, 

 chemical and production measurements off the coast of 

 Peru, 28 May - 22 June, 1969 aboard the RV THOMAS 

 WASHINGTON. IMR Rep. 70-5. (Unpublished man- 

 uscript.) 



' University of California, Institute of Marine Re- 

 sources. 1971. Research on the marine food chain; 

 progress report, July 1970 - June 1971. Part III. Data 

 record. Cruise PIQUERO, Leg 7. Section 2. The plank- 

 ton. IMR Rep. 71-10. (Unpublished manuscript.) 



Burd (1969) on board the Peruvian research 

 vessel SNP-1 during the first week of PIQUERO 

 7 in an area south of Callao. 



Since neither Strickland et al. (1969) nor 

 Ryther et al. (1970) provided quantitative evi- 

 dence to support the hypothesis that grazing 

 may be an important means of regulating the 

 phytoplankton crop in these waters, one purpose 

 of our present studies was to determine the 

 abundance of the zooplankton — both micro- 

 zooplankters (see Beers and Stewart, 1970) and 

 larger forms — and to relate this to observations 

 on phytoplankton abundance, growth rates, and 

 taxonomic composition. In addition, we were 

 interested in the "disappearance" of the patches 

 with time. Evidence is examined for a sugges- 

 tion that patches may dissipate through physical 

 mechanisms such as horizontal and vertical mix- 

 ing. The detailed study of physical variables 

 has provided insight into factors affecting bio- 

 logical production in the waters off Peru which 

 would not have been appreciated by the biologist 

 working independently. 



MATERIALS AND METHODS 



Studies were conducted between 13 and 22 

 June 1969, in the approximate area bounded by 

 lat 10° and 12° S and long 78° and 79° W off 

 Supe. Extensive "surface" mapping operations 

 at various times throughout this period with 

 underway continuous analysis of inoi'ganic nu- 

 trients, phytoplankton pigment fluorescence, and 

 temperature allowed for the detection and sur- 

 veillance of two patches of upwelled water in 

 this area. Water for the mapping as well as 

 for other "surface" sampling described below 

 was taken with a pump fitted into the ship's 

 hull about 3 m below the sea surface. This unit 

 delivered 10 to 11 liters/min through plastic 

 piping. A series of 57 discrete stations were 

 made during the period of observing the patches 

 for sampling the microzooplankton and macro- 

 zooplankton populations, obtaining water for 

 primary i)roduction measurements and phyto- 

 plankton enumeration, and for determining 

 temperature and salinity profiles. These were 

 taken from various depths in and below the 

 euphotic zone within and outside of the patches. 



860 



