WEBB and COROLLA: BURST SWIMMING OF NORTHERN ANCHOVY 



40 I 



36 

 32 



_J u> 



\ 



Umax =20.8 L+ 1.95 (r^ =0.891) 



•=Ur 



J ! I I I I I L 



J I I I I 



0.2 0.4 0.6 0.8 1.0 12 1.4 1.6 



TOTAL LENGTH (cm) 



Figure 4. — Maximum burst speeds ( U max • as a function of total 

 length (L) for northern anchovy larvae. Solid circles are absolute 

 speeds ( cm/s). Crosses show specific speeds in body lengths ( L/s) 

 calculated as Umax/L. Vertical bars show ± 2 SE. 



by predators so that endurance must be added to 

 these components of predator-prey behavior. Of 

 these three factors the physical ability to turn 

 seems least important. Fish can turn in extremely 

 small radius circles (Webb 1976; Eaton et al. 1977; 

 Kimmel et al. in press) so that the optimal escape 

 strategy of turning inside a predator's turning 

 radius, forcing the predator to stop and reorient 

 (Rowland 1974), is probably impractical. For ar- 

 tificial predators, nets, the scale of the net makes 

 turning ability unimportant. Therefore, speed is 

 expected to be the major performance component 

 of larval behavior contributing to the outcome of 

 encounters with their prey, while both speed and 

 endurance will affect interactions with predators 

 and nets. 



Hunter (1972) found that northern anchovy lar- 

 vae accelerated over 8-16 ms to reach their prey. He 

 found that a 0.8 cm larva would travel about 0.04 

 cm in that time, and a 1.3 cm larva about 0.09 cm. 

 In the present experiments, the distance traveled 

 was 0.03 and 0.09 cm in 12 ms for larvae of 0.8 and 

 1.3 cm TL, respectively. This shows that northern 

 anchovy larvae use their maximum burst perfor- 

 mance in attacking their prey. 



Northern anchovy larvae are also prey items for 



0.4 0.6 0.8 10 L2 

 TOTAL LENGTH (cm) 



L4 



L6 



Figure 5. — Mean burst speeds (U) as a function of total length 

 (L) for northern anchovy larvae. Solid circles are absolute speeds 

 (cm/s) and crosses show specific speeds (U/L). Vertical bars show 

 ± 2 SE. The 10 body length/s relationship is based on Blaxter 

 (1969). The intermittent swimming speed relationship is taken 

 from Hunter (1972). Stars show mean voluntary burst speeds, 

 from Hunter (1972). 



a variety offish and invertebrates (Hunter 1977, in 

 press) so that the larvae would require a variety of 

 response patterns to attempt to escape from preda- 

 tion. For example, lunging predators typically 

 overshoot the prey location (Hoogland et al. 1956; 

 Hunter 1972) when the rapid acceleration in a fast 

 start would facilitate escape by quickly removing 

 the potential prey from the predator's strike path. 

 The rapid improvement in maximum burst speed 

 with size (Figure 4) should reduce the vulnerability 

 of larger northern anchovy to such predators. 

 Chasing predators, for example, juvenile fish and 

 larvae of more active species such as scombrids, 

 are at the opposite extreme to lunging predators. 

 Northern anchovy larvae should have reduced 

 vulnerability to such predators as they grow be- 

 cause of improved mean swimming speed during a 

 burst (Figure 5). In addition, the distance traveled 

 per burst increases with size, implying improved 

 stamina with increasing total length which should 

 further facilitate escape of larger larvae from 

 chasing predators. 



The effect of size on the ability of northern an- 

 chovy larvae to escape natural predators and the 

 mechanisms involved in escape behavior have re- 

 ceived little attention. Decreased vulnerability of 

 larger larvae to predation by copepods and 



147 



