larvae (Fig. 3). The proportion of small anchovy 

 larvae escaping attack was also low {67c ) but in- 

 creased with size to 737r of 22 mm larvae 

 (Folkvord and Hunter 1986). The numbers of lar- 

 vae escaping attack were significantly different 

 between anchovy and sardines at sizes larger 

 than about 13 mm. Conversion of lengths to age 

 using field growth rates does not eliminate the 

 differences between sardine and anchovy (Fig. 4). 

 Sardine larvae older than 20 days were more vul- 

 nerable to predation than anchovy larvae of the 

 same age (Fig. 4). 



100 I— 



o 



z 



5 



z 

 o 

 a 



V) 



z 



lU 



O 

 a. 



UJ 

 Q. 



80 



60 



40 



20 



ANCHOVY .f 



V..--  



-SARDINE 



8 12 16 



LENGTH (mm) 



20 



24 



Figures. — Increase by size of the percentage of Pacific sardine 

 larvae, Sardinops sagax, and northern anchovy larvae, En- 

 graulis mordax, escaping attack by adult northern anchovy and 

 95'^ confidence intervals. Data on anchovy larvae from 

 Folkvord and Hunter (1986). 



Figure 4. — Increase by age of the percentage of Pacific sardine 

 larvae, Sardinops sagax, and northern anchovy larvae, En- 

 graulis mordax, escaping attack by adult northern anchovy and 

 95% confidence intervals. Size categories of reared larvae have 

 been converted to ages using growth rates estimated from the 

 field. Data on anchovy larvae from Folkvord and Hunter (1986). 



Discussion 



The proportion of Pacific sardine larvae re- 

 sponding to attack and escaping attack increased 

 with size and with age. Our results differ from 

 those reported by Folkvord and Hunter (1986) for 

 anchovy larvae in the rate at which sardine lar- 

 vae respond and escape attacks at given sizes and 

 ages. It should be noted that, although the 

 methodology was the same, the observers were 

 different. This difference could affect rate of re- 

 sponse to attack. It also should be noted that the 

 size of adult anchovy used by Folkvord and 

 Hunter (1986) ranged from 83 to 89 mm SL, 

 whereas the size range was 84-95 mm SL in our 

 study and that the size of predator influences the 

 number of larvae escaping (Folkvord and Hunter 

 1986). The slightly larger size of predators used in 

 this study is not sufficient to explain difference in 

 escapement, nor is the difference in observer 

 likely to affect the rate of escapement since the 

 observer's task is to examine whether the larvae 

 are escaping or are being eaten. 



The greater vulnerability to predation of sar- 

 dine larvae than anchovy larvae has interesting 

 implications. In general, larger larvae are less 

 vulnerable to predation than small larvae. Bailey 

 (1984) and Bailey and Batty (1983) compared the 

 vulnerability of cod, flounder, plaice, and herring 

 larvae to predation by invertebrate predators. 

 They found that herring larvae were the least 

 vulnerable larvae because herring were more re- 

 active and had the greatest escape speeds. Sar- 

 dine larvae are larger at hatching and at a given 

 age are larger than anchovy larvae. In our exper- 

 iment sardine larvae react to predatory attacks at 

 similar rates as anchovy larvae, but escape attack 

 at a much lower rate. 



This difference in vulnerability to attack may 

 be due to differences in swimming behavior. An- 

 chovy larvae swim using beat and glide locomo- 

 tion (Hunter 1972). The escape behavior is usu- 

 ally a burst of swimming from a motionless 

 position (Folkvord and Hunter 1986). We ob- 

 served that sardine larvae, however, swim contin- 

 uously and they respond to attack by changing 

 direction and increasing speed. This difference in 

 swimming mode may affect escape behavior in 

 two ways. The escape behavior of sardine larvae 

 may be less flexible than that of anchovy larvae 

 because the direction the sardine larvae takes is 

 largely determined by its trajectory. Since sar- 

 dine larvae cruise, their scope for activity (escape 

 behavior) may be limited. Anchovy larvae accel- 



166 



