316 MARINE BIOTIC COMMUNITIES 



stages of invertebrates and a few fishes (Bovard and Osterud, 1919; 

 Weese and Townsend, 1921; Strong, 1925). 



Nekton. The larger animals with effective swimming powers in 

 this area consist chiefly of fishes and mammals (Shelford and Powers, 

 1915; Shelford, 1918, a; Powers, 1921). 



Fishes 



Culpea pallasii (Cuy. & Val.) Herring 



Hypomesus pretiosus (Gir.) Surf smelt 



Thaleichthys pacificus (Rich.) Eiilachon 



Oncorhynchus nerka (Walb.) Sockeye salmon, anadromous 



Oncorhynchus kisutch (Walb.) Silver salmon, anadromous 



Oncorhynchus gorbuscha (Walb.) Hump-back salmon, anadromous 



Mammals 



Orcinus rectipinna (Cope) Killer whale 



Rhachianectes glaucus (Cope) Gray whale 



Globicephala scammonii (Cope) Pacific blackfin 



Phocaena phocaena (L.) Porpoise 



The killer whale appears to be most abmidant and was frequently 

 seen in the San Juan Channel; the blackfin was noted less often. 

 Originally, gray whales congregated in muddy bays and came to the 

 surface daubed with bottom mud (Scammon, 1874). 



Coaction and Reaction. The food coactions among North Pacific 

 plants and animals are little known, though the work of Lebour 

 (1919-1923) on the North Atlantic makes possible inferences as to the 

 food of plankton animals and young fishes in general. The food 

 habits of only a few adult fishes have been studied. The killer whale 

 is known to prey upon other w'hales and fishes, salmon especially 

 being mentioned by Scammon (1874) ; the same author states that 

 the blackfin feeds upon squids and fishes. The reaction of pelagic 

 organisms in shutting out much light from the waters below has al- 

 ready been noted (Shelford and Gail, 1922; Shelford, 1929, b). In 

 addition to this, plankton organisms, sinking to the bottom at death, 

 absorb oxygen and produce carbon dioxide (Atkins, 1922), as well 

 as sulphur compounds and organic mud, having a profound effect 

 upon bottom conditions, especially in quiet water. 



Physiological Characters. The independence of the bottom and 

 shores is striking. Most of the work on physiological characters has 

 been concerned w^ith fishes, w^hich are very sensitive to differences in 

 the character of the water. The heri'ing responds to variations of 

 0.1° C. in temperature and is sensitive to changes of 0.1 pH. The re- 

 sistance of the pelagic herring and surf smelt to carbon dioxide was 

 rated as 10 and 8 respectively, while the viviparous perch,, an in- 



