NOTES 



ADDITIONAL EVIDENCE SUBSTANTIATING 



EXISTENCE OF NORTHERN 



SUBPOPULATION OF NORTHERN 



ANCHOVY, ENGRAULIS MORDAX 



The northern anchovy, Engraulis mordax 

 (Girard), ranges from Queen Charlotte Islands, 

 British Columbia, to Cape San Lucas, lower 

 Baja California. A study of variations in meristic 

 characters (McHugh 1951) and genetic studies 

 using serum transferrins (Vrooman and Smith 

 1971) generally support the hypothesis that 

 three distinct subpopulations exist within this 

 species' total geographic range. The dividing 

 lines between subpopulations apparently occur 

 at Point Conception, Calif, (delineating the north- 

 ern and central elements), and at Cedros Island, 

 central Baja California (delineating the central 

 and southern elements). 



Extensive spawning activity by the central 

 and southern subpopulations is evidenced from 

 the results of comprehensive egg and larvae 

 surveys conducted since 1951 by the California 

 Cooperative Oceanic Fisheries Investigations 

 (Baxter 1967). Although these surveys suggest 

 that the time-space distributions of spawning 

 effort by these two subpopulations tend to overlap, 

 evidently each achieves enough reproductive iso- 

 lation to generate genetic differences between 

 serum transferrins. Apparently, then, the central 

 and southern subpopulations are capable of 

 independently producing their own recruitment. 



Until recently, the evidence for independent 

 spawning by the northern subpopulation was 

 not extensive. Ahlstrom ( 1968) noted that, in 1949 

 and 1950, anchovy larvae were found in moderate 

 abundance off the Oregon coast. LeBrasseur 

 (1970) indicated that a small number of larvae 

 were taken in a 1958 survey of Queen Charlotte 

 Sound, British Columbia. Waldron^ stated that 

 no eggs or larvae were taken in incidental 

 samples off the Washington-Oregon coast in 1966 

 but that a few anchovy larvae were obtained 

 during a comprehensive survey in the spring 

 of 1967. 



Such meager results might lead one to believe 

 that the few larvae observed in northern waters 

 were merely the result of incidental spawning 

 activity. A conclusion might then be made that 

 the northern subpopulation does not indepen- 

 dently produce its own recruitment but relies 

 instead upon an influx of anchovies from the 

 two southern subpopulations. 



In 1969, however, Richardson (1973) encoun- 

 tered such extensive numbers of anchovy larvae 

 during a May-October survey of larval fishes 

 off the Oregon coast (lat. 42°00'-46°30'N, coast- 

 line — long.l29°30'W) that the above conclusions 

 seemed to be refuted. Her results indicated the 

 presence of a spawning stock of anchovies as- 

 sociated with the warm, near-surface waters of 

 the Columbia River plume. Moreover, the peak 

 of spawning seemed to be correlated with that 

 period in summer when warm plume water 

 (>14°C) was a dominant oceanographic feature. 



Evidence from Length-Frequency Distributions 



An analysis of age- and length-frequency 

 distributions played a major role in determining 

 stock structure for the Pacific sardine, Sardinops 

 sagax. A similar analysis of length-frequency 

 distributions was undertaken for the northern 

 anchovy. The following review outlines the 

 rationale and criteria applied in the sardine 

 analysis and adapted for this study. 



Early sardine investigators at first hypothe- 

 sized that three subpopulations composed this 

 species' total west coast population^. However, 

 in addition to evidence of only sporadic spawn- 

 ing activity (Ahlstrom 1954), age- and length- 

 frequency distributions obtained from the so- 

 called northern subpopulation failed to reveal 

 the presence of the most recently produced 

 age-groups, i.e., the O's, I's, and 2's (Harry 

 1948). These ages, however, were often observed 

 in samples from the central and southern sub- 

 populations. The consistent absence of O's from 

 northern samples presumably confirmed a lack 



'Waldron, K. D., Northwest Fisheries Center, National 

 Marine Fisheries Service, NOAA, Seattle, Wash., pers. commun. 

 1971. 



^A northern subpopulation supposedly ranged from British 

 Columbia southward to central California, while central and 

 southern subpopulations resided respectively off southern 

 California ana lower Baja California. 



212 



