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 Pauly, D. 



1981. The relationship between gill surface area and growth 

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morhua) estimated from stomach contents and growth rates. 



Dana 5:65-80. 



W. Silvert 



Department of Fisheries and Oceans 

 Marine Ecology Laboratory 

 Bedford Institute of Oceanography 

 Dartmouth, Nova Scotia, Canada B2Y kA2 



International Center for Living Aquatic 



Resources Management 

 MC P.O. Box 1501 

 Manila, Philippines 



D. Pauly 



EFFECT OF A RIVER-DOMINATED ESTUARY 

 ON THE PREVALENCE OF CARCINONEMERTES 



ERRANS, AN EGG PREDATOR OF 

 THE DUNGENESS CRAB, CANCER MAGISTER 



Carcinonemertes errans is a host-specific nemertean 

 that can destroy large numbers of Dungeness crab, 

 Cancer magister, eggs (Wickham 1979, 1980). Al- 

 though the ectosymbiotic nemertean is present on 

 adult and juvenile crabs of both sexes, its only 

 known detrimental effect is to the egg stage. Wick- 

 ham (1979) estimated that the direct mortality to 

 eggs of Dungeness crabs off central California was 

 55%. High egg mortalities in the San Francisco, CA, 

 area were suggested as a possible cause of the 

 drastic decline in Dungeness crab populations in that 

 area (Fisher and Wickham 1976; Wickham 1979). 

 From November 1983 through October 1985, the 



National Marine Fisheries Service (NMFS) con- 

 ducted a comprehensive study of the distribution, 

 abundance, and size-class structure of Dungeness 

 crabs in the Columbia River estuary, a river-domi- 

 nated estuary. Limited sampling was also done in 

 adjacent coastal areas. As an incidental part of the 

 study, we examined crabs for C. errans, and ob- 

 served an effect of the river-dominated estuarine 

 environment on the prevalence of C. errans on 

 Dungeness crabs. 



Methods 



The study was done in the lower Columbia River 

 estuary and adjacent coastal areas (Fig. 1). The 

 estuary is a drowned river mouth that is dominated 

 by river flows. Highest flows typically occur during 

 the spring and lowest flows during late summer and 

 fall. Estimated river flows (monthly averages) dur- 

 ing the study period ranged from 3,121 m^/s 

 (August 1985) to 14,091 m^/s (May 1985) (U.S. Geo- 

 logical Survey, Portland, OR). Salinities fluctuate 

 widely in the estuary depending on river flow, tidal 

 stage, and distance from the river mouth (Neal 

 1972). Inversely related to river flows, the salinity 

 intrusion is typically least during spring and great- 

 est during late summer and fall. 



Sampling was done monthly at a maximum of 28 

 estuarine and ocean sites (Fig. 1). At 26 of the sites, 

 an 8 m semiballoon shrimp trawl with stretched 

 mesh size of 38.1 mm was used to collect samples; 

 a 9.5 mm Hner was inserted in the cod end of the 

 net to prevent escape of small Dungeness crabs. 

 Sampling in the estuary was normally done during 

 times of higher salinity (early flood to early ebb tide). 



Generally a subsample of at least 100 Dungeness 

 crabs (^20 mm) from each trawl effort was mea- 

 sured to the nearest mm (carapace width, anterior 

 to the 10th anterolateral spines), weighed, sexed, 

 and checked for eggs and C. errans. Specific body 

 areas— the undersurface of the abdomen, the 

 thoracic area covered by the abdomen, and the pleo- 

 pods— were examined for C. errans. Dungeness crab 

 catches at individual stations varied considerably, 

 ranging from to >100 crabs per trawl effort. Crabs 

 <20 mm were measured and weighed, but were not 

 routinely sexed or checked for C. errans. 



Dungeness crabs were separated into four size 

 classes: I (<50 mm), II (50-99 mm). III (100-129 mm), 

 and IV (>129 mm). We used the chi-square test to 

 compare the prevalences of C. errans on crabs in 

 the ocean and the estuary and to compare the level 

 of infestation between males and females within the 

 two areas. 



140 



FISHERY BULLETIN: VOL. 85, NO. 1, 1987, 



