MAKGULIES: VULNERABILITY AND SENSORY DEVELOPMENT OF WHITE SEABASS 



Larval Responses 



The probability of a white seabass larva re- 

 sponding to or escaping a predatory attack gen- 

 erally increased with larval size, although major 

 differences in these responses were apparent de- 

 pending upon type of fish predator. The mean 

 percentage of larvae escaping attacks by north- 

 ern anchovy ranged fi'om 37c in yolk-sac larvae (3 

 mm SL) to 43% in metamorphosing fishes (15 

 mm SL) (Fig. 2A). while the percentage re- 

 sponding to anchovy attacks ranged from 14% 

 (yolk-sac stage) to 56% (at metamorphosis) (Fig. 

 2B). Mean predation rate (percentage of larvae 

 eaten in 10 minutes) by anchovy predators de- 

 creased from 95% on yolk-sac larvae to 56% on 

 early juveniles (Fig. 2A). The predator/prey 

 interactions were best described by exponential 

 regi'essions (Fig. 2). 



White seabass larvae were better able to 

 respond to or escape attacks of juvenile white 

 seabass than those of northern anchovy. Mean 

 percentage of larvae escaping white seabass at- 

 tacks ranged from 8% for yolk-sac larvae to 74% 

 for metamorphosing fishes (Fig. 3A), while the 

 percentage responding to attacks increased from 

 18% (yolk-sac stage) to 84% (at metamorphosis) 



(Fig. 3B). Responses and escapes from juvenile 

 white seabass improved significantly in larger 

 larvae, particularly between the larval sizes of 

 7.5 versus 9.0 mm SL (i-test, P < 0.01). Re- 

 sponse and escape success nearly doubled during 

 this developmental stage. Mean predation rate 

 by juvenile white seabass predators decreased 

 from 80% on yolk-sac larvae to 65% on 6 mm 

 larvae, increased to 87% on 7.5 mm larvae, and 

 then steadily decreased to 30% on early juveniles 

 (Fig. 3A). These predation functions also were 

 fit to exponential regressions (Fig. 3). 



The success of avoidance movements by re- 

 sponding larvae (numbers escaping/numbers re- 

 sponding) generally increased with larval size 

 (Table 3). Approximately 21% of responding 

 larvae in the 3.1 mm size category successfully 

 escaped northern anchovy attacks; this percent- 

 age increased to 50% in 4.5 mm larvae and 75% 

 at metamorphosis. Avoidance success from juve- 

 nile white seabass attacks ranged fi'om 397f for 

 3.1 mm larvae to 75% for 7.0 mm individuals and 

 improved to nearly 90%^ in early juveniles. 



Statistical comparison of the responses and 

 escapes from northern anchovy versus white 

 seabass predators indicated that a significantly 

 higher percentage of larvae >6.0 mm SL 



Figure 2. — Vulnerability of white seabass larvae to 

 adult northern anchovy predators as a function of lar- 

 val length. A. SoUd circles are percentage of larvae 

 escaping an attack, error bars are 2 x SE, regression 

 equation is Arcsine Y = 5.078 (."'-"sl (,, = 44 ,.2 ^ 

 0.73), where Y = proportion of larvae escaping and SL 

 = larval standard length (mm); open circles are per- 

 centage of larvae eaten in 10 min trials, error bars are 

 2 X SE, regression equation is Arcsine Y = 81.326 

 g-n.03oSL (,^ = 44^ ^ = 0.96), where Y = propor- 

 tion of larvae eaten in 10 minutes and SL = larval 

 standard length (mm). B. Percentage of larvae re- 

 sponding to an attack, error bars are 2 x SE, regres- 

 sion equation is Arcsine Y = 15.293 e" "^'sl („ = 44 ,i 

 = 0.89), where Y = proportion of larvae responding 

 and SL = larval standard length (mm). 



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