2 86 Memoir Sears Foundation for Marine Research 



ditions — "provided they are present in numbers large enough to overwhelm the host" 

 {liy- 12). Furthermore, it has been reported that nematodes, cestodes, and trematodes 

 occur in the viscera and sporozoa in the muscles of small fish taken at Woods Hole, 

 Massachusetts {85: 473). 



Mass Mortalities and Diseases. The literature that deals with the Atlantic Herring 

 contains many accounts of their great destruction on both sides of the North Atlantic. 

 For June and July 19 14, Cox reported widespread mortality on both the southern and 

 western sides of the Gulf of St. Lawrence {28: 82—85). -^ ^^^ years later, a spectacular 

 event occurred in Cohasset Harbor, Massachusetts Bay, on October 5, 1920, when an 

 estimated 20,000 barrels of fish 100-125 "^"^ ''°"g became stranded on the mud with 

 a falling tide {16: 104). On October 10 a second but smaller run and on October 15 

 a run as large as the first were stranded similarly. The exact reason for the stranding 

 and mass destruction was not determined, but fishermen thought that the fish had 

 been driven into the nearly landlocked harbor by silver hake, Merluccius bilinearis. 

 Other mass strandings of small individuals have also been reported, for Manchester 

 Harbor, Massachusetts {14: 327). Pursuit by predatory fishes is the most likely cause 

 of simultaneous mass strandings within small areas; for an eyewitness account of one 

 such event, see page 285. 



But enough evidence has now accumulated to make it practically certain that 

 when mortality is very widespread it has been caused by disease of one kind or 

 another. Thus Cox found that fish from the Gulf of St. Lawrence case of 19 14 (above) 

 were so evidently in a diseased condition and were so heavily infested with a myxo- 

 sporidian protozoan that it seems practically certain that the latter had been responsible 

 for the mortality {28: 82—85). It is known now that those along the coasts of New 

 England, and presumably in more northern waters, suffer from fungous disease caused 

 by Ichthyosporidium, from ulcer disease caused by protozoa, from pigment spot disease 

 caused by larval trematode worms, and from tail rot caused by bacteria; it is known 

 also that fungous disease in particular, and probably the others as well, sometimes 

 reaches epidemic proportions, with mortality so widespread and so severe that the sardine 

 fishery is very seriously affected.'^ 



Relationships. Although the Pacific herring has been recognized as being specifi- 

 cally distinct from the North Atlantic Herring and has for many years been designated 

 Clupea pallasii Cuvler and Valenciennes, it is difficult In the light of rather recent studies 

 to find distinguishing characters. This difficulty was pointed out by Rounsefell, who 

 made some studies of the relationship himself and reviewed the findings of several 

 European investigators {ill: 243). The distinguishing character given by Regan in 

 his revision of the Clupeldae is "Ventral scutes all keeled" in harengus and "Ventral 

 scutes In front of pelvic fins not keeled" in pallasii (106 : 227). According to the material 

 now at hand, the scutes in pallasii are merely less strongly developed." 



15. For a general survey, with photographs, of diseased fish, and references, see Sindermann and Rosenfield {117). 



16. Relationships with the species of temperate southern hemisphere waters have not been adequately worked out. 

 Regan, the most recent revisor, had inadequate material {106: zz&). Norman did not attempt to compare the South 



