Responsiveness of Starved Northern 



Anchovy Engraulis mordax Larvae 



to Predatory Attacks by Adult Anchovy 



Clelia Booman 



La Jolla Laboratory, Southwest Fisheries Science Center 



National Marine Fisheries Service. NOAA, P.O. Box 271, La Jolla, California 92038 

 Present address: Zoological Laboratory, University of Bergen 

 Allegate 45, N-5007 Bergen, Norway 



Arild Folkvord 



La Jolla Laboratory, Southwest Fisheries Science Center 



National Marine Fisheries Service, NOAA, P.O Box 271, La Jolla, California 92038 

 Present address. Department of Fisheries and Marine Biology, University of Bergen 

 High Technology Centre. N-5020 Bergen, Norway 



John R. Hunter 



La Jolla Laboratory. Southwest Fisheries Science Center 



National Marine Fisheries Service. NOAA. P.O. Box 271, La Jolla, California 92038 



Most studies of larval mortality 

 have been on food, feeding, and 

 starvation, with less work done on 

 predation and even fewer studies on 

 the interaction between starvation 

 and predation (Hunter 1984). Vul- 

 nerability to predation is a product 

 of the probability of encounter be- 

 tween prey and predator, and prey 

 susceptibility (Bailey and Houde 

 1989). Starvation could affect one 

 or both of these components: star- 

 ving larvae might be less able to 

 avoid attacks by predators than fed 

 ones (Rothschild et al. 1982). On the 

 other hand, a decrease in conspicu- 

 ousness of starved larvae might 

 reduce their probability of encoun- 

 ter with predators (Gamble and Fui- 

 man 1987). In addition, slow growth 

 caused by an inadequate food sup- 

 ply could result in larvae remaining 

 in the length-classes most vulner- 

 able to predation and thereby in- 

 crease larval losses (Shepherd and 

 Cushing 1980). 



In northern anchovy Engraulis 

 mordax larvae, vulnerability to pre- 

 dation by fishes is size-specific, thus 

 slower growth could result in 

 greater losses (Webb 1981, Folk- 



vord and Hunter 1986). The objec- 

 tive of this study was to evaluate 

 the effect of starvation on avoid- 

 ance performance of northern an- 

 chovy. We estimated the respon- 

 siveness and escape ability of 9 mm 

 SL (standard length) anchovy to 

 predatory attacks by adult anchovy 

 as a function of days of starvation. 

 We also developed histological star- 

 vation criteria which link the nutri- 

 tional condition of larvae to their 

 responsiveness to attacks by fish 

 predators. This could allow an as- 

 sessment of the interaction between 

 predation by fishes and starvation 

 in the sea, because the nutritional 

 condition of sea-caught larvae could 

 be assessed using histological cri- 

 teria (O'Connell 1976 and 1980, 

 Theilacker 1978 and 1986). 



Materials and methods 



Rearing and 

 experimental design 



About 4000 northern anchovy eggs 

 produced by a captive brood stock 

 (Leong 1971) were placed in a 100- 

 liter black fiberglass tank main- 



tained at 16.0-17.4°C (mean 16.2° 

 C). Except for minor differences, 

 larvae were reared following the 

 procedure outlined by Hunter (1976). 

 Larvae were reared until they 

 reached 9 mm live standard length 

 (about 20 days posthatch) at which 

 time they were used in our experi- 

 ments. In the experiments, 9 mm 

 larvae were used because smaller 

 anchovy larvae respond less fre- 

 quently (<36%) to predators (Folk- 

 vord and Hunter 1986). 



When larvae reached 9 mm, they 

 were separated into two groups by 

 transferring about half of them to 

 another 100-liter tank containing 

 only filtered seawater. The trans- 

 ferred larvae were never fed. Avoid- 

 ance performance of the starved 

 larvae was compared with that of 

 larvae fed daily in the original tank. 

 Initially a series of tests was con- 

 ducted to estimate if the transfer of 

 larvae affected avoidance perfor- 

 mance. In these tests both groups 

 were fed and one was transferred. 

 Mortality was higher in the trans- 

 ferred group over the first day, but 

 no significant difference existed 

 between the groups thereafter in 

 mortality or in their response to 

 predators using the behavioral 

 methods outlined below. 



Larvae from three different rear- 

 ing groups were used. In two 

 groups, none of the starved larvae 

 survived more than 6 days, and in 

 one group a few survived 7 days. 

 Considering all groups together, 

 about 50% of the starved larvae sur- 

 vived 4-5 days and only 1% sur- 

 vived 7 days of starvation. Thus, 

 most of the data are for larvae 

 starved for 1-5 days. Four groups 

 of five adult anchovy (90- 107 mm 

 SL) were used as predators. Pred- 

 ators were placed in the test con- 

 tainer (a fiberglass tank 0.75x2.15 

 x 0.83m with a glass window on one 

 side) about 3 weeks prior to a series 

 of experiments. Ambient seawater 



Manuscript accepted 10 July 1991. 

 Fishery Bulletin, U.S. 89:707-711 (1991). 



707 



