FISHERY BULLETIN: VOL. 84, NO. 4 



PREDATOR - Scomber Japonicus 



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ESCAPING ATTACK 



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LARVAL STANDARD LENGTH (mm) 



Figure 3.— Vulnerability of northern anchovy larvae and juveniles to juvenile chub 

 mackerel predators as a function of anchovy length. A, percentage of northern 

 anchovy larvae escaping attack; bars are 2 x SE; line is Weibull curve fit to six 

 points using Marquardt's least squares method (Pielou 1981); equation is N = K(\ 

 - exp (1 - (Lib) - A)) where K = 0.66, b = 27.41, N = percentage of larvae, L 

 = larval length, and A = 2.12; and predation rate of chub mackerel predators 

 (percentage eaten in 5 min) where dashed line is data when experiments with biased 

 predator feeding motivation are omitted. B, percentage of northern anchovy lar- 

 vae that responded to the attack of a chub mackerel, bars are 2 x SE; and Weibull 

 parameters for curve are K = 0.93, 6 = 12.61, and A = 1.24. 



Predation Rates 



The predation rate of northern anchovy (propor- 

 tion of larvae consumed by northern anchovy 

 predators in 5 min) reached a maximum somewhere 

 between larval lengths of 8.5 and 15 mm when all 

 data were used, but it occurred between larval 

 lengths of 8.5 and 11 mm when we deleted the ex- 

 periment where northern anchovy predator perfor- 



mance was lower than average (dashed line in 

 Figure 2A). Statistical comparisons of the fraction 

 of larvae consumed in the various size classes in- 

 dicated that 6.8 mm larvae were taken less often 

 than larvae in 8.5, 11, and 15 mm size classes despite 

 the fact that these larvae had a low escape ability 

 (P < 0.05; normal approximation to the binomial 

 mean; n = 35, 48, 40, and 60, for 5.9, 8.5, 11, and 

 15 mm size classes). Owing to their small size and 



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