OWEN ET AL.: SPAWNING AND SURVIVAL OF LARVAL ANCHOVY 



Larval Condition 



Starvation incidence was estimated from his- 

 tological criteria on 141 anchovy larvae from Site 

 1 and on 119 larvae from Site 2. The larvae were 

 collected with nonquantitative bongo nets towed 

 to 50 m. Although the best preservation pro- 

 cedure for histological samples is to preserve 

 larval fish in Bouin's fixative within 3 minutes 

 after capture, 5-6 minutes were required to 

 obtain representative samples to 50 m. After 

 fixing in Bouin's fluid for 24-48 hours, samples 

 were transferred to 707c ethyl alcohol for 

 storage. 



The nutritional state of northern anchovy 

 larvae is usually classified by grading the ap- 

 pearance of tissues of the brain, cartilage, 

 notochord, liver, pancreas, and gut (O'Connell 

 1976). But because many of these tissues had 

 lysed owing to extended time before preserva- 

 tion, an additional criterion was used in this 

 study. This criterion, the height of midgut 

 mucosal cells, was unaffected by the 5-6 minutes 

 needed to fix the larvae (Theilacker and 

 Watanabe 1989). Heights of midgut mucosal cells 

 were divided into three categories (healthy, 

 intermediate, and starved) according to labora- 

 tory results (Theilacker and Watanabe 1989). As 

 northern anchovy develop past 6 mm SL, the 

 midgut folds to increase the absorptive area. The 



fold makes it difficult to measure cell heights of 

 larger larvae. To apply the durations determined 

 for the laboratory fish to the field samples, the 

 size of the field-collected larvae was adjusted to 

 equal the size of preserved laboratory fish of 

 known feeding history (Theilacker 1980). Details 

 of these manipulations are given in Theilacker 

 and Watanabe (1989). 



RESULTS 



Environmental Variations Within and 

 Between Drifters and Sites 



Surface Drift 



Drifters were tracked as shown in Figure 2. 

 Released 10 nmi apart at Site 1, Drifters A and B 

 moved generally eastward, away from Santa 

 Catahna Island, on slightly convergent courses. 

 Mean speeds over theii' 2.7 days at sea were 17. 1 

 cm/s and 18.7 cm/s (about 15.5 km/dy). Range of 

 speeds measui-ed by drifter displacements over 8 

 h intervals were 5.6-34.7 cm/s and 6.8-32.9 cm/s. 



Released 5 nmi apart at Site 2, Drifters A and 

 B moved in a southeast-trending arc, again on 

 sUghtly convergent courses. Mean speeds over 

 their 2.5 days at sea were 34.6 cm/s and 37.4 

 cm/s (about 30 km/d), twice as fast as at Site 1. 

 Speed ranges measured were 15.3 cm/s to 45.4 



34'N 



50' - 





40" 



11 33'30" 



I— 



< 



_J 



20' 

 10' 



33-N 

 11 



SITE 1 



/.J^y 22/2208 40 



20/0823^ XY £k 



20/0615 ^ A ^ 23/0335 



8-30' 20' 10' 118'W 50' 119"W 50' 40' 118*30' 



LONGITUDE LONGITUDE 



Figure 2. — Drifter trajectories along Sites 1 and 2. 



677 



