STEVENS AND ARMSTRONG: CANCER MAGISTER IN GRAYS HARBOR 



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FIGURE 2. — Temperature-salinity profile for crab sampling 

 sites 1-12, Grays Harbor, Wash. Filled circles indicate mean 

 density +1 SE of crabs for the entire study, as determined by 

 trawl; open circles indicate mean bottom salinity at low tide. 

 Crab densities are not plotted for stations 10-12 where ring nets 

 were used. 



more stable in the outer estuary, but less so as 

 distance increased eastward from the harbor 

 mouth. At station 3, bottom temperatures ranged 

 from 7 C C (winter) to 14°C (summer), while at sta- 

 tion 9 they ranged from 5° to 18°C. Vertical stratifi- 

 cation was greater toward the head of the estuary 

 and less so in the outer estuary as a result of 

 turbulent mixing. Greatest vertical salinity dif- 

 ference measured during the study was 17%» at 

 station 9. Grays Harbor receives 70-100 in of rain- 

 fall annually, and stratification was greatest dur- 

 ing November-March, the period of peak rainfall. 

 Flow rates of the Chehalis River, which contrib- 

 utes 80% of the freshwater inflow, varied from 22.3 

 mHr 1 in August 1980 to 2,322 mHr 1 in Febru- 

 ary 1981 (data provided by U.S. Geological Sur- 

 vey). 



Spatial Distribution of 

 Crab Population 



Complete records (width, sex, age) were ob- 

 tained for 14,556 crabs. Coefficients of variation 

 averaged 0.53 for the trawls and 0.46 for the ring 

 nets, implying that both techniques had a similar 

 degree of precision. 



Mean density of crabs during the 14-mo sam- 



pling period was greatest at station 1 (2,190 crabs 

 ha -1 ), and catches declined with increasing dis- 

 tance from the estuary mouth and decreasing bot- 

 tom salinity (Figs. 2, 3A). Notable exceptions to 

 this pattern were low densities at stations 6 and 2 

 (120 and 290 crabs ha" 1 , respectively; Fig. 3). Sta- 

 tion 2 was concurrently being used as a dredged 

 sediment disposal site by the U.S. Army Corps of 

 Engineers. 



Crabs caught by ring net were more abundant at 

 station 11, near the eastern (upstream) end of the 

 estuary than at station 10, and averaged 22.9 and 

 12.7 crabs net - \ respectively, from June to October 

 (Fig. 3F). No crabs were caught at station 12 except 

 in August and September 1980. 



Temporal Distribution of 

 Crab Population 



Megalops larvae were found as early as 1 April 

 1980 at station 6, and in densities up to 810/1,000 

 m 3 at station 5 on 22 April 1980. 



Crab densities at all stations were greatest from 

 May to August 1980 (Fig. 3A-E) and declined from 

 September 1980 through January 1981. Lowest 

 densities occurred in October and November 1980, 

 none being >200 crabs ha -1 except at station 1. 

 Although monthly variation was great at each 

 station, this general decline in crab density dur- 

 ing fall-winter occurred throughout the estu- 

 ary. 



Crab abundance at the three ring-net stations 

 (10, 11, and 12) increased dramatically from June 

 through October 1980, then dropped in November 

 1980 to a low of <1.0 crabs net - 1 at all three sta- 

 tions (Fig. 3F). No crabs were caught at station 12 

 except during August and September 1980, when 

 the salinity reached 9 and TL, respectively. Salin- 

 ity at station 12 was 1.0'/, or less during all other 

 sampling periods. 



The F- tests showed that mean crab density in 

 the outer estuary (stations 2, 3, and 4) was sig- 

 nificantly greater (P = 0.011) than in the inner 

 estuary (stations 7, 8, and 9; Table 2). Crab density 

 at all six stations (2, 3, 4, 7, 8, and 9) was signifi- 

 cantly greater (P = 0.001) in spring-summer than 

 in fall-winter 1980-81. Regression analysis of 

 log 10 -transformed density data on bottom salinity, 

 temperature, and Chehalis River flow rate showed 

 no significant dependence of trawl catches on 

 these variables, but salinity alone was responsible 

 for about 40% of the variance in crab abundance at 

 the ring net stations (10, 11, and 12; r 2 = 0.398, P = 

 0.001). 



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