LAROCHE and RICHARDSON: REPRODUCTION OF NORTHERN ANCHOVY 



spawning frequency depended on the, as yet, un- 

 proven assumption that all mature females in the 

 central subpopulation spawn during 1 mo of the 

 peak spawning period. Even if this assumption is 

 correct the dependence of this method on obtain- 

 ing samples which accurately reflect the propor- 

 tion of spawning and nonspawning females in the 

 population poses another problem. Spawning fre- 

 quency will be overestimated if nonspawning 

 females are not as susceptible as spawning fish to 

 capture by sampling gear because of differences in 

 spatial distribution or behavior of the two groups. 

 Our oocyte observations alone, without data on 

 rates of oocj^e maturation and degeneration, did 

 not yield an estimate of northern anchovy spawn- 

 ing frequency in the northern subpopulation. But 

 our findings indicated that oocyte degeneration 

 and apparent reduced growth among 

 intermediate-sized, yolked oocytes prior to and 

 after release of one batch of oocytes may limit the 

 number of subsequent spawnings. In addition, the 

 actual length of the spawning season off Oregon 

 and Washington is only 2 mo, although water 

 temperatures favorable for northern anchovy 

 spawning (13°-17.5° C at 10 m depth, Baxter 1967) 

 are present in this region for 5-6 mo. This discrep- 

 ancy supports our interpretation of the oocyte ob- 

 servations by indicating that environmental fac- 

 tors may not be suitable for complete maturation 

 of all yolked oocytes present in northern anchovy 

 ovaries in the northern subpopulation. Only data 

 from laboratory experiments designed to deter- 

 mine rates of oocyte maturation (and degenera- 

 tion) under varying environmental conditions, 

 such as photoperiod, temperature, and food supply, 

 will provide a definitive answer to the question of 

 how many times northern anchovies spawn per 

 year. 



Seasonal Distribution Associated 

 with Reproduction 



A distinct geographic segregation of mature and 

 immature northern anchovies and hence an in- 

 ferred spawning migration during the summer- 

 time spawning season occurs in the northern sub- 

 population off Washington, Oregon, and northern 

 California but apparently not around British Co- 

 lumbia. Evidence for this resulted from a sum- 

 mary of data from a number of sources including 

 data and cruise reports (Table 8), Tillman,^ and 

 personal observations from our own sampling ef- 

 forts (Table 1, Figure 1). These seasonal patterns in 



the northern subpopulation, described here for the 

 first time, were evident even though the data were 

 obtained with various types of sampling gear and 

 unequal sampling effort. 



In winter, January through March, both mature 

 and immature northern anchovies of all sizes 

 ( =50-180 mm) occur in nearshore coastal areas off 

 British Columbia, Washington, and Oregon. Small 

 schools were seen in British Columbia coastal 

 waters. Concentrations were found off Washing- 

 ton between Cape Flattery and Destruction Island 

 (over 31-313 m depths) and between Grays Harbor 

 and the Columbia River (42-101 m depths). Off 

 Oregon, northern anchovies were taken between 

 the Columbia River and Coos Bay (91-183 m 

 depths) with largest numbers occurring between 

 the Columbia River and Tillamook Bay. Fish off 

 Washington and Oregon were observed or cap- 

 tured near the bottom or in midwater in coastal 

 areas, but were not commonly taken in bays and 

 estuaries. Small catches offish were taken in the 

 Strait of Juan de Fuca but none were taken in 

 Puget Sound, Wash.; Yaquina Bay, Oreg; or Hum- 

 boldt Bay, Calif. A few rare occurrences ( 50-70 mm 

 FL) have been reported from Tillamook Bay, Oreg. 



In spring, April through mid-June, northern 

 anchovies still occur in nearshore coastal waters. 

 Fish, 80-160 mm SL, were taken in the seine 

 fishery of the 1940's in British Columbia coastal 

 waters. Although no schools were observed off the 

 northern Washington coast, northern anchovies, 

 50-170 mm SL, were consistently taken near the 

 bottom or in midwater in the vicinity of the Co- 

 lumbia River mouth (20-91 m depth). Northern 

 anchovies, mostly <100 mm, were collected in the 

 spring in Tillamook Bay, Yaquina Bay, and Coos 

 Bay, Oreg. (sizes not given). Northern anchovies of 

 all sizes entered Humboldt Bay in April and re- 

 mained there into June and July. 



In summer, mid-June through September, both 

 mature and immature anchovies (up to 160 mm 

 SL) occur in nearshore coastal waters of British 

 Columbia where they supported a major seine 

 fishery in the 1940's. Although few ripe or spent 

 adults were taken, spawning is reported to occur 

 in bays and inlets around southern British Co- 

 lumbia in summer. Off Washington and Oregon, 

 sexually mature and immature northern an- 

 chovies are geographically separated. Adult fish 



^M. F. Tillman, Northwest and Alaska Fisheries Center 

 Marine Mammal Division, NMFS, NOAA, 7600 Sand Point Way 

 NE, Seattle, WA 98115, pers. commun. April 1975. 



615 



