water volume, however, in this study 

 they were generally comparable at the 

 time of the October and May surveys. 

 Water temperatures were similar from 

 surface to bottom through both sur- 

 veys. Depths at sample sites were 

 greater during the May survey and may 

 reflect fresher runoff conditions . 



and Durkin and Emmett (1980). How- 

 ever, scour area invertebrate densi- 

 ties were considerably lower than 

 those found in nearby estuarine em- 

 bayments by these same investigators. 



CONCLUSIONS 



BENTHIC 



INVERTEBRATES 



Taxonomic groups and species 

 captured in the 80 October and May 

 samples are listed in Table 3. In- 

 cluded are the sites and surveys 

 where they occurred. There were 43 

 groups or species listed with the 

 highest diversity found at Tansy 

 Point and the Interstate Bridge. 

 Some epibenthic invertebrates spe- 

 cies were captured with the infau- 

 na grab-sampler and others with the 

 trawl. Epifauna include the bivalues 

 Corbicula manilensis and Mytilus 

 edulis , several species of mysids, 

 crangon shrimp, Dungeness crab, cope- 

 pods, cladocerans and Trichoptera. 



Comparative abundance of ben- 

 thic invertebrates is shown for the 

 four sites and two survey periods 

 in Table 4. The density of infauna 

 organisms was low at all sites in 

 October although copepod epifauna 

 at the Interstate Bridge provided 

 an appearance of numerical impor- 

 tance. The May survey results re- 

 vealed greater infauna densities at 

 all four sites. Increases occurred 

 in nearly all groups, but particu- 

 larly the Amphipoda, Nematoda, and 

 Copepoda . Jhe densities of organ- 

 isms per m were greater than pre- 

 viously reported in estuarine sam- 

 pling studies at or near the navi- 

 gation channel by Sanborn (1973, 

 1975), Higley and Holton (1975, 1978) 



Hydraulic forces which maintain 

 water depths at the four study sites 

 apparently result in a uniform sub- 

 strate which accumulates little sedi- 

 mentary material. Benthic infauna 

 densities increased substantially 

 between surveys though there was no 

 obvious change in sediment particle 

 size. Some of the sites appear to 

 have substantial numbers of pelagic 

 schooling fish, demersal fish and 

 shellfish. Fish examined for food 

 utilization consumed other fish, zoo- 

 plankton, insects, a variety of epi- 

 fauna, and benthic amphipods . The 

 amphipod most frequently consumed, C. 

 salmonis, is an infauna tube-dwelling 

 species that apparently migrates into 

 the water column because it was con- 

 sumed by both pelagic and demersal 

 fish. 



On the basis of the inventory, 

 the Jetty A site would be suggested 

 as a test disposal site particularly 

 in October and November, whereas 

 Tongue Point would be excluded from 

 further consideration. The Inter- 

 state Bridge site, though not as 

 valuable as Tongue Point, should also 

 be excluded from a test disposal 

 effort. Tansy Point may have po- 

 tential as a test disposal site 

 though further evaluation is needed, 

 particularly during the active dredg- 

 ing season. A test disposal program 

 should provide for an evaluation of 

 fisheries and infauna by preliminary 

 and post disposal sampling. The 



448 



