FISHERY BULLETIN: VOL. 74, NO. 4 



biomasses given here, but not all (see Table 1), 

 have been corrected for contamination by phyto- 

 plankton. The correction was made as follows. The 

 amount of chlorophyll a was determined in a 

 '/4-aliquot by SCOR methods (UNESCO 1966) and 

 partitioned among the four subsamples according 

 to inspection of the preserved samples. The in- 

 spection indicated approximate relative amounts 

 of phytoplankton in the samples. The chlorophyll 

 weight for each subsample was converted to 

 carbon following Lorenzen (1968) and then to wet 

 weight according to Gushing et al. (1958). The 

 correction generally reduced the original biomass 

 by less than 10% but occasionally up to 30%. All 

 biomasses shown in Figures 2 to 4 have been 

 corrected. 



The preserved samples of zooplankton <500 jum 

 were not examined for ichthyoplankton, because 

 few specimens (except some newly hatched larvae) 

 were expected to pass through a SOO-jnm sieve. For 

 eggs of Engraulidae, which are oval and measured 

 from 500 to 580 jum (mean 570 /xm) in transverse 

 diameter in our material, our numbers per haul 

 could have been slightly too low because of losses 

 through the 500-jum sieve. It is unlikely that these 

 losses were high. During a later cruise 

 (AUFTRIEB 1975) in the same area, we counted 

 engraulid eggs in the catches of two Bongo nets of 

 uniform mesh sizes, 300 and 500 ixm, but otherwise 

 identical and hauled side by side in the same net 

 assembly. Egg numbers were 122 and 145, so the 

 300-/xm net retained no more than the 500-jLim net. 



Temperature and Chlorophyll a 



These properties were measured from hydro- 

 graphic casts which used plastic 5-liter Niskin 

 bottles with reversing thermometers. Sampling 

 depths in the upper 200 m were usually 0, 3, 10, 20, 

 30, 50, 75, 100, 150, and 200 m, depending on the 

 bathymetry. Concentrations of chlorophyll a were 

 determined by SCOR methods (UNESCO 1966) 

 and integrated in milligrams per square meter. 

 The integration program summed the area of each 

 depth integral using the area formula of a 

 trapezoid. Samples for chlorophyll a were gener- 

 ally not taken below 75 or 100 m, because results 

 of other casts showed little chlorophyll below those 

 depths. 



Area and Periods of Study 



Almost all the zooplankton hauls and hydro- 

 graphic casts of JOINT-I were made in the area 



888 



shown in Figures 1 and 5. They were generally 

 made along an east-west line at about lat. 21°40'N, 

 where series of hauls and casts (not always 

 together) were frequently repeated. Figure 5A 

 shows the positions of all zooplankton hauls made 

 in the area. Nine other hauls were scattered in 

 space and time in adjacent areas, and are not used 

 in this paper. No distinction is made here between 

 day and night hauls. Hauls on the shelf were made 

 mostly by day and those on the slope mostly at 

 night. Eggs are of more interest than larvae in this 

 study as explained above and should have been 

 equally available by day and night. Larvae might 

 have avoided the nets more by day than by night. 



The total period of JOINT-I in which zooplank- 

 ton hauls were made was 8 March to 10 May 1974. 

 It was divided by port calls into three parts. Legs 

 1, 2, and 3 (Table 2). The periods of these legs (first 

 to last zooplankton haul) were 8 to 24 March, 1 to 14 

 April, and 22 April to 10 May. 



Ten series of hauls were made together with 

 hydrographic casts along lat. 21°40'N, each series 

 occupying 1 to 3 days. Figures 2 to 4 show data for 

 some of the series and Table 1 summarizes data for 

 all of them. 



Table 2.— Principal categories of fish eggs and larvae taken on 

 JOINT-I in the area of Figure 5, showing numbers per square 

 meter averaged for hauls on each leg of the cruise and summed 

 for the cruise. 



IDENTIFICATION AND 

 ENUMERATION OF 

 EGGS AND LARVAE 



The eggs and larvae from all stations in Figure 

 5A were identifiable in the categories shown in 

 Table 2. Most of the identifications were made at 

 the Institut fur Meereskunde from the large collec- 

 tions, literature, and experience of northwest 



