Spawning and Survival Patterns of Larval Northern 



Anchovy, Engraulis mordax, in Contrasting 



Environments — ^A Site-Intensive Study 



R. W. Owen. N. C. H. Lo, J. L. Butler, G. H. Theilacker, A. Alvarino, 

 J. R. Hunter, and Y. Watanabe 



ABSTRACT: During the 1985 spawning season of 

 the northern anchovy, Engraulis mordax Girard, 

 off southern California, a serial field study at con- 

 trasting sites linked measurable environmental 

 characteristics with parameters of larval anchovy 

 growth and survival and determined a range of en- 

 vironmental conditions over which northern an- 

 chovy had recently spawned. Surface and water 

 column characteristics were measured while fol- 

 lowing surface drifters at each site, and their re- 

 lation to corresponding measurements of larval 

 anchovy production, growth, mortality, and starva- 

 tion are reported. 



The nearshore site was eutrophic with low cur- 

 rent speeds, low wind speeds, and high forage levels 

 which are characteristic of coastal spawning areas. 

 The offshore site, by contrast, was relatively oligo- 

 trophic and had higher surface mixing rates, a 

 deeper mixed layer, reduced stability in the pycnoc- 

 line, and lower forage levels. 



Among the measured characteristics of the 

 ichthyoplankton, only one, the larval production 

 rate, was markedly different at the two sites. Al- 

 though habitat suitability for adult anchovies was 

 different, sur\'ival probability for larval anchovies 

 was more equivalent at the two sites than inspec- 

 tion of single parameters of the environment sug- 

 gested. In contrast with the view that the northern 

 anchovy spawns indiscriminately, the results of 

 this study suggest that components of the adult 

 northern anchovy population tend to spawn under 

 conditions and at levels that yield consistent sur- 

 vival probabilities for their offspring. 



Since Lasker's (1975, 1978, 1981) pioneering 

 work on causes of larval fish mortality, recent 



developments have made techniques available to 

 assess age-specific larval growth, mortality, and 

 physiological condition. These developments 

 have piqued interest in field studies that link 

 environmental processes to survival probabili- 

 ties for larvae of broadcast spawners. Here we 

 present the results of a site-intensive shipboard 

 study that combined newly available measures of 

 larval condition with a suite of physical and biotic 

 measures of their environment in the Lagi'an- 

 gian setting provided by near-surface drifters to 

 determine local variations of a few days dura- 

 tion. Our results are intended to guide the de- 

 sign and execution of programs that address the 

 recruitment process and its relation to the 

 spawning environment. 



Conditions under which northern anchovy, 

 Engraulis mordax Girard, spawn and under 

 which their eggs and larvae survive presently 

 are known mainly from cruises of the CalCOFI 

 progi'am, which are quasi-synoptic surveys of 

 broad areas of the spawning domain during 

 which limited sets of environmental observations 

 and measurements have been made (cf. Reid 

 1988). Owing to limits imposed by time and 

 resources, such surveys do not yield knowledge 

 of the local fate of spawned products because the 

 methods that characterize survival hkelihood of 

 larval fish have only recently been developed 

 and verified, and because local changes (those 

 embedded in the surface flow) are not knowable 

 by the survey approach. 



METHODS 



R. W. Owen, Marine Environment & Resources, 1431 Inde- 

 pendence Way, Vista, CA 92084 and Scripps Institution of 

 Oceanography, Code A-003, La Jolla, CA 92093. 

 N. C. H. Lo, J. L. Butler, G. H. Theilacker, A. Alvarino, 

 and J. R. Hunter: Southwest Fisheries Center La Jolla 

 Laboratory, National Marine Fisheries Service, NCAA, 

 P.O. Box 271, La .Jolla, CA 92038. 



Y. Watanabe, Tohoko Regional Fisheries Research Labora- 

 tory, Fisheries Agency, Shiogama, Miyagi 985, Japan. 



Manuscript accepted April 1989. 

 Fishery Bulletin. U.S. 87: 673-688. 



Site Selection 



Criteria for selection of the two study sites 

 were that each must 1) show evidence of recent 

 spawning by anchovy, 2) contrast with the other 

 site in macroscopic setting and environmental 

 character, and 3) exhibit no local gradients indic- 

 ative of smaller scale (0.1-10 km) environmental 



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