ington coastal waters each spring. Coho returning 

 to the coast south of their natal stream would subse- 

 quently undergo the observed northward spawning 

 migration. Each of these authors conceded however, 

 that certain stocks or different portions of the same 

 stocks may follow entirely different migratory 

 routes. Scarnecchia (1981) felt that many coho pro- 

 duced along the west coast may either remain in ad- 

 jacent coastal waters or move directly south after 

 emigration from freshwater. 



The dispersal pattern of 437 coho salmon tagged 

 off northern California early in the 1971 and 1972 

 seasons clearly showed the northward movement of 

 adult coho out of California (O'Brien 1973). Nearly 

 all of the tagged fish recaptured in California were 

 caught in May and June of each year while tagging 

 was still being conducted. Oregon recoveries peak- 

 ed in July and the first half of August, while most 

 Washington recoveries occurred during the latter 

 half of August through September. 



California's share of the recaptured coho tagged 

 off northern California (O'Brien 1973) was 9.3% in 

 1971 and 8.8% in 1972. These percent returns are 

 very similiar to California's 13.0% and 8.3% share 

 of the O.P.I, area catch in 1971 and 1972 respective- 

 ly. Because, for practical purposes, one can assume 

 that all of the coho caught in California originate 

 to the north, the similarity between California's catch 

 and tag returns would indicate that nearly all O.P.I, 

 area coho stocks were off California during the tag- 

 ging period. This supposition is extreme, but the 

 results do suggest that a major portion of the coho 

 ultimately caught in the O.P.I, area each year are in 

 California waters during spring. The northward 

 migration of large numbers of coho is further sup- 

 ported by the northward progression of peak 

 monthly catches within the O.P.I, area (Pacific 

 Fishery Management Council 1983), and the 

 monthly catch distribution of hatchery marked coho 

 (Hopley 1978). 



Survival Indices Comparison 

 and Discussion 



Dungeness crab, unlike coho salmon, do not move 

 any appreciable distance, therefore local landings are 

 considered to be a good indicator of local abundance 

 In California seasonal landings are composed of at 

 least three year classes, however northern Califor- 

 nia landings are generally dominated by 4-yr-old crab 

 (Warner 1985), while central California landings, 

 because of a faster growth rate, are dominated by 

 3-yr-old crab (Collier^). 



An alignment of Dungeness crab seasonal landings 



with their dominant or "primary" year classes (Fig. 

 4) generates reasonably representive year class in- 

 dices, if it is taken into consideration that extreme- 

 ly abundant year classes, such as the 1966 and 1972 

 year classes in northern California, probably 

 dominate landings for more than 1 yr (Methot and 

 Botsford 1982). The Dungeness crab year class in- 

 dices (Fig. 4) suggest that a period of poor landings 

 in both central and northern California during the 

 early 1960's (Fig. 2) reflects poor survival of the 

 1958-60 year classes. 



As mentioned earlier, northern California landings 

 have been characterized by large seemingly cyclic 

 fluctuations, the cause of which has been the sub- 

 ject of considerable research and debate (see Methot 

 and Botsford 1982; Botsford 1984, for a review of 

 this work). Of the hypotheses generated by these in- 

 vestigations. Wild et al. (1983) presented, in my opin- 

 ion, the most tenable explanation for this particular 

 period of low survival. They attributed the drop dur- 

 ing this period to a reproductive failure caused by 

 an unprecedented warming of coastal waters 

 associated with the 1957 El Nino (the "warm water 

 years" 1957-59, Radovich 1961). 



The apparent recruitment of Dungeness crab to 

 the northern California population of a "normal" 

 year class in 1961 (Fig. 4), with the return of "nor- 

 mal" environmental conditions, ushered in several 

 years of good survival. This recovery was not 

 duplicated in the central California population, 

 where a drop in the strength of the 1961 year class 

 anteceded an extended period of poor survival. Wild 

 et al. (1983) further proposed that a major change 

 in the oceanic regime off central California is the 

 primary cause of the continued poor survival there, 

 although they do concede that ocean temperatures 

 in certain years appear to have been favorable to 

 Dungeness crab survival. Wickham (1979), on the 

 other hand, suggested that the central California 

 population has reached a new equilibrium, with 

 worm predation now being the dominant biological 

 control. It has yet to be proven which, if either, of 

 these mechanisms is the primary cause of the con- 

 tinued poor survival in central California. 



Alternatively, a direct comparison of O.P.I, catches 

 with central California Dungeness crab year class 

 indices (Fig. 5) illustrates a long-term inverse rela- 

 tionship which developed with the first recruitment 

 of hatchery-reared coho salmon stocks in 1961. O.P.I, 

 area landings are used to express the annual sur- 

 vival of coho potentially impacting central Califor- 



'P. Collier, California Department of Fish and Game, 619 Second 

 St., Eureka, CA, 95501, pers. commun. November 1984. 



686 



