BURST SWIMMING PERFORMANCE OF NORTHERN ANCHOVY, 



ENGRAULIS MORDAX, LARVAE 



R W. Webb' and R. T. Corolla^ 



ABSTRACT 



Burst swimming performance was measured for northern anchovy larvae from 0.23 to 1.33 cm total 

 length at a temperature of 17° C. Fast starts and burst swimming were initiated using a 3 V/cm direct 

 current electric shock. Performance was measured from movie film recorded at 250 frames/s. Percent- 

 ages of larvae responding to the stimulus increased from 99c 40 hours after eggs were spawned to a 

 maximum of 95 ±4% after 125 hours. Distances traveled in a given time period increased linearly with 

 length so that maximum speed (f/max) and mean speed ({/) similarly increased linearly with total 

 length (L) according to [/max = 20.8 L + 1.95; U = 8.18 L + 4.89. The maximum distance traveled per 

 burst (Smax' was used as a measure of endurance and increased with length according to S max = 3.79 L 

 + 0.08. These swimming speeds and endurance relationships can explain a large portion of size- 

 dependent selectivity of towed plankton nets. 



Larval swimming performance has been the focus 

 of several studies (Blaxter 1969; Rosenthal and 

 Hempel 1970; Hunter 1972). These have em- 

 phasized sustained swimming speeds which are 

 considered an important factor affecting the vol- 

 ume of water searched by a larva, and hence food 

 density requirements or the encounter frequency 

 with food items. These low levels of activity appar- 

 ently affect ration and at the same time are major 

 contributors to routine energy expenditures 

 (Vlymen 1974). 



In contrast, very high activity levels (fast starts 

 and steady burst swimming) are rare. While they 

 are unlikely to constitute a large metabolic load, 

 high speeds are essential to the act of capturing 

 food items (Hunter 1972) and in escaping from 

 predators. This aspect of larval performance has 

 not been evaluated. Therefore, the purpose of this 

 work was to determine the effect of size on burst 

 swimming performance (acceleration and sprints) 

 for northern anchovy, Engraulis mordax, larvae, 

 and to evaluate the importance of such high levels 

 of activity in prey capture and escape from preda- 

 tors, including nets. 



'Southwest Fisheries Center La Jolla Laboratory, National 

 Marine Fisheries Service, NOAA, La Jolla, Calif.; present ad- 

 dress: University of Michigan, School of Natural Resources, Ann 

 Arbor, MI 48109. 



^Southwest Fisheries Center La Jolla Laboratory, National 

 Marine Fisheries Service, NOAA, La Jolla, Calif.; present ad- 

 dress: Southampton College, Southampton, NY 11968. 



METHODS 



Northern anchovy larvae were reared from eggs 

 as described by Hunter (1976). Eggs were spawned 

 from five groups of parents taken from laboratory 

 stocks on five separate occasions during the fall of 

 1979 (Table 1). Eggs were transferred to noncircu- 

 lated filtered seawater in 400 1 black fiber glass 

 tanks. Food for the larvae was the dinoflagellate 

 Gymnodinium splendens for 2- to 5-d-old larvae, 

 and thereafter the rotifer Brachionus plicatilis. 

 Water temperature was maintained at 17° C. Lar- 

 vae were held under constant illumination from 

 standard room fluorescent lights. 



Experiments were performed on larvae of 11 dif- 

 ferent total lengths, ranging from 0.23 to 1.33 cm. 

 Observations were concentrated on larvae in the 

 first few days after hatching (Table 1) when 

 greatest larval development occurs (O'Connell in 

 press). 



Groups of 5-50 larvae were observed using 

 Schlieren optics. Details of this system are given 

 in Holder and North (1963). Briefly, a vertical col- 

 limated light beam was produced by a high inten- 

 sity monochromatic point source at the focus of a 

 concave mirror attached to the ceiling. A second 

 mirror on the floor focused the light on a black spot 

 on a glass plate. The focal length of the mirrors 

 was 140 cm. 



A cylindrical tank, 17 cm in diameter and 5 cm 

 deep, with parallel plate glass top and bottom, was 

 introduced into the light beam. Discontinuities in 



Manuscript accepted July 1980. 



FISHERY BULLETIN: VOL. 79, NO. 1, 1981. 



143 



