Paramoeba perniciosa have been found from 

 Maryland to Georgia (Sprague et al. 1969; Mahood 

 et al. 1970), and strong correlations were estab- 

 lished between mass mortalities of blue crabs, 

 high incidences of infection, and declines in com- 

 mercial fishery landings (Mahood et al. 1970). Per- 

 centages of blue crabs infected with the disease 

 range from 20 to 35% of captive animals in holding 

 boxes (Sprague and Beckett 1966; Sawyer 1969) 

 and from 7 to 17% in wild populations during the 

 summer (Sawyer 1969; Sawyer et al. 1970; New- 

 man and Ward 1973). As noted by Newman and 

 Ward, epizootics attributed to this disease can be of 

 short duration, killing significant numbers of 

 animals and leaving no indication of the severity 

 even to investigators purposefully seeking clues 

 on occurrence and extent of infection. 



The importance of these observations is, in part, 

 as a reminder that significant loss from a popula- 

 tion can result from factors other than predation. 

 The nature of other mortality factors (be they dis- 

 ease, physical-chemical, or pollution) and the 

 magnitude of their effects are largely unknown, 

 particularly for highly mobile crustaceans. Still, 

 the presence of over 6,400 dead adult female crabs 

 along a segment of coastline in conjunction with 

 the other two reports of mass mortality noted, 

 indicates C. magister is susceptible to conditions 

 and events that may occur on a seasonal basis. It is 

 reasonable to assume that the crabs observed dead 

 at the high watermark were only a fraction of the 

 numbers affected offshore and, if so, then the 

 magnitude of the mortality in this instance was 

 certainly greater than that observed. 



Whatever the cause of the mortality to C. 

 magister in this case, and whether such an event is 

 a common seasonal occurrence or a rare catas- 

 trophe, a partial loss of this reproductively sig- 

 nificant age-group could have important conse- 

 quences for the commercial fisheries. 



Acknowledgments 



We express our appreciation to Walt Cooke and 

 Dennis Tufts of the WDF, to Albert Sparks of the 

 National Marine Fisheries Service, and to Darrell 

 Demory of the Oregon Department of Fish and 

 Wildlife for sharing their observations with us. 



reared larvae of the T)\xngeness crab, Cancer magister, and 



possible chemical treatments. J. Invertebr. Pathol. 



28:329-336. 

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1978. Behavior of age-specific, density-dependent models 



and the northern California Dungeness crab (Cancer 



magister) fishery. J. Fish. Res. Board Can. 35:833-843. 

 BUTLER, T. H. 



1961. Growth and age determination of the Pacific edible 



crab Cancer magister Dana. J. Fish. Res. Board Can. 



18:873-891. 



Cleaver, F C. 



1949. Preliminary results of the coastal crab (Cancer 

 magister) investigation. Wash. Dep. Fish., Biol. Rep. 

 49A:47-82. 



MAHOOD, R. K., M. D. Mckenzie, S. J. bollar, J. R. Davis, 

 and D. Spitsbergen. 



1970. A report on the cooperative blue crab study - south 

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Newman, M. W, and G. E. Ward, Jr. 



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 22:329-334. 



POOLE, R. L. 



1967. Preliminary results of the age and growth study of 

 the market crab (Cancer magister) in California: The age 

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SAWYER, T. K. 



1969. Preliminary study on the epizootiology and host- 

 parasite relationship of Paramoeba sp. in the blue crab, 

 Callinectes sapidus. Proc. Natl. Shellfish Assoc. 59: 

 60-64. 



SAWYER, T. K., R. COX, AND M. HIGGINBOTTOM. 



1970. Hemocyte values in healthy blue crabs, Callinectes 

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 perniciosa. J. Invertebr. Pathol. 15:440-446. 



Sprague, v., and R. L. Beckett. 



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Sprague, v., R. L. Beckett, and T. K. Sawyer. 



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Bradley G. Stevens 

 David a. Armstrong 



College of Fisheries 

 University of Washington 

 Seattle, WA 98195 



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