HUNTER: BEHAVIOR OF LARVAL ANCHOVY 



INCOMPLETE FEEDING SEQUENCES 



Feeding sequences often ended before they 

 were completed by execution of the strike. The 

 mean frequency of feeding strikes (the last act 

 in the feeding sequence) for all visual observa- 

 tions for larvae of ages 4 to 27 days was 1.28 ±: 

 0.14 strikes/min (N = 325) whereas that for 

 the orientation movement of the head (the first 

 act in the sequence) was 3.22 ± 0.30. Thus, 

 about 40% of all feeding sequences were com- 

 pleted. The proportion of feeding sequences 

 that were completed did not change with age, 

 but there was some indication that the propor- 

 tion of incomplete sequences increased when the 

 larvae began to feed on Artemia nauplii. This 

 increase in the proportion of incomplete sequen- 

 ces was caused by an increase in the proportion 

 of sequences ended at the first act, the orienta- 

 tion movement of the head. The proportion of 

 feeding sequences that were carried as far as 

 bending the body was 52% and remained about 

 the same regardless of age or food type. 



In the film analysis I analyzed only incomplete 

 feeding sequences that were continued beyond 

 the head orientation movement and compared 

 them with completed sequences. These measure- 

 ments indicated that some feeding sequences 

 ended at every stage up to and including the final 

 strike posture, and the duration of incomplete 

 sequences overlapped that of completed ones 

 (Table 4) . The only characteristic measured in 

 the photographs that consistently separated in- 

 complete from completed feeding sequences was 

 that at the end of incompleted ones the prey was 

 farther away from the larvae than it was in 

 completed sequences. Thus, the principal cause 



Table 4. — Comparison of characteristics of incomplete 

 and complete feeding sequences for larval anchovy 

 5.1-10.0 mm. 



of the failure to continue a feeding sequence was 

 an inability to closely approach the prey while 

 forming the strike posture. 



To summarize, photographic analysis of in- 

 complete and complete feeding sequences indi- 



2.0 



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N=IO 



1.5 



1.0 



^ 0.5 

 Q 



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k. 



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 12.0 



TOTAL 

 SEQUENCE 



S-POSTURE 



APPROACH 



I I I I I I I I I 



LO 



0.0 



BODY 

 AMPLITUDE 



DISTANCE 

 TO PREY 



I-VJ ^ 1 L. 



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 0) 

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E 

 E 



Q 

 UJ 

 UJ 

 Q. 

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10 



STRIKE 



- S-POSTURE 

 FORWARD 

 MOVEMENT 



10 



20 



J I I 



10 



15 



20 



1 A^ = 19. 

 ' N = 13. 



5 10 



LARVAL LENGTH (mm) 



Figure 6. — Characteristics of complete feeding sequences 

 of anchovy larvae taken from film analysis. Values are 

 means ± 2 X SE for three size classes of larvae (5.1- 

 10.0, 10.1-15.0, and 15.1-20.0) and are plotted at the mean 

 length of the larvae in the class. 



829 



