Southeast Fisheries Center Galveston Laboramry 



National Marine Fisheries Service, NOAA 



Jt700 Avenue U 



Galveston, TX 77550 



Present address: 1 78 Plaza Circle 



Danville, CA H526 



Dennis A. Emiliani 

 K. Neal Baxter 



Southeast Fisheries Center Galveston Laboratory 

 National Marine Fisheries Service, NOAA 

 4700 Avenue U 

 Galveston, TX 77550 



A POSSIBLE LINK BETWEEN COHO 



(SILVER) SALMON ENHANCEMENT AND 



A DECLINE IN CENTRAL CALIFORNIA 



DUNGENESS CRAB ABUNDANCE 



Dungeness crab, Cancer magister, are taken com- 

 mercially along the west coast of the contiguous 

 United States from Avila, CA, to Destruction Island, 

 WA (Fig. 1). During the early years of the Califor- 

 nia Dungeness crab fishery, effort was concentrated 

 on the central California population which produced 

 most of the state's landings (Fig. 2). The northern 

 population subsequently became the major con- 

 tributor to California's landings after an expansion 

 of the fishery there during the 1940's. 



Northern California landings (Fig. 2) generally 

 have followed a fluctuating pattern similar to one ex- 

 pressed in Oregon and Washington; however, land- 

 ings from the relatively isolated central California 

 population failed to recover from a coastwide low 

 during the early 1960's. The lower landings reflect 

 a long-term reduction in abundance which has been 

 variously attributed to egg predation by a nemer- 

 tean worm Carcinonemertes errens (Wickham 1979) 

 and to the effects of a long-term change in oceanic 

 conditions (Wild et al. 1983). 



The failure of the central California population to 

 recover from the coastwide period of low abundance 

 also occurred about the time coho salmon, Oncorhyn- 

 chus kisutch, reared in Oregon and Washington 

 hatcheries began to make a significant contribution 

 to the west coast salmon fishery (Oregon Depart- 

 ment of Fish and Wildlife 1982). The effect of 

 salmonid predation on commercially important 

 marine crustaceans has received little attention, 

 although it is suspected that predation by salmonids 

 introduced into a number of both small and large 



freshwater lakes (Nilsson 1972; Morgan et al. 1978) 

 has substantially altered the abundance and species 

 composition of their planktonic crustacean com- 

 munities. Since numerous salmonid food habit 

 studies (Heg and Hyning 1951; Petrovich 1970; Reilly 

 1983a) show that planktonic Dungeness crab 

 megalops are a major component of the coho salmon 

 diet, it is conceivable that an increase in the coho 

 predation rate associated with an influx of hatchery 

 coho into the central California region is at least par- 

 tially responsible for the prolonged decline in 

 Dungeness crab landings. 



In this paper I first present evidence showing that 

 a large portion of the coho salmon ultimately caught 

 each summer off the west coast are in California 

 waters during spring, the period Dungeness crab 

 megalops are most abundant. I then compare and 

 contrast survival indices to determine if the temporal 

 variation in survival of both species is consistent with 

 the predator-prey hypothesis. 



Oregon Production Index Area Coho 



Each spring and summer, a single coho salmon 

 brood (year class) is recruited to the commercial 

 salmon fishery off California, Oregon, and southern 

 Washington, an area collectively referred to as the 

 Oregon Production Index area or O.P.I, area (Oregon 

 Department of Fish and Wildlife 1982). These fish 

 entered the ocean to feed in May and June of the 

 previous year, after having spent about 18 months 

 in freshwater. Coho caught in the O.P.I, area before 

 1961 (Fig. 3) were predominately wild stocks. These 

 stocks had declined to extremely low levels by 1960; 

 however, the successful introduction of Oregon and 

 Washington hatchery-reared coho resulted in a 

 return to historical landing levels during the 1960's 

 and 1970's. Much of the hatchery fish responsible 

 for the increased landings are derived from early 

 return Tbutle River coho, which tend to enter 

 fisheries south of their stream of origin (Hopley 

 1978). 



Coho salmon made up only 10% or less of Califor- 

 nia's ocean salmon catch prior to the development 

 of Oregon and Washington enhancement programs 

 (FVy 1973). Most of these wild coho originated in the 

 streams and rivers of Oregon and Washington (Allen 

 1965) and were landed primarily in the northern 

 California ports of Crescent City and Eureka. The 

 recruitment of hatchery fish increased the average 

 annual coho contribution to 25% of the total ocean 

 salmon catch, with the central California ports of 

 San Francisco and Fort Bragg accounting for a con- 

 siderably larger portion of the total coho catch. 



682 



FISHERY BULLETIN: VOL. 83, NO. 4, 1985. 



