BIOLOGY AND NATURAL HISTORY 111 



number of dams and obstructions have been placed in the rivers. However, 

 since 1900 the annual take has fluctuated considerably with a low of about 

 6 million pounds in 1937 and a high of nearly 15 million pounds in 1934. Such 

 fluctuations are most probably the result of differences in abundance rather 

 than in economic factors. The price of alewives remains nearly constant (one 

 cent per pound) regardless of peak or lean years. Merriman (1941) has 

 shown that in the case of the striped bass, abundance depends to a large 

 extent on the survival rate of the young in various years; the survival rate 

 in turn depends on conditions of temperature, wind, water flow, predation, 

 and food for the young. Production and survival of a large number of young 

 are then represented in the fishery in succeeding years in proportion to the 

 age of the fish composing the commercial catch. Fluctuations in alewife 

 production, therefore, are believed to result largely from biological and 

 climatic factors. 



SHAD 



Alosa sapidissima (Wilson) 



The shad, a member of the herring family, was until 1935 the most impor- 

 tant food fish of North Carolina in terms of value. It was an important 

 species along the entire Atlantic coast since it supported a commercial fishery 

 in every state. The spring spawning runs were known in every suitable river 

 from the St, Johns River in Florida to the St. Lawrence. Since the great 

 decline in the fishery, beginning shortly before the turn of the century, the 

 shad runs in a number of streams are of historic interest only. Several factors 

 are involved in the collapse of the fishery; these will be discussed later. 



The shad, like the alewife, is anadromous, living in salt water but ascend- 

 ing coastal streams to spawn. The earliest shad runs occur in Florida, begin- 

 ning in November or December. These are followed, in succession, by runs 

 in the streams in Georgia, South Carolina, North Carolina, and up the coast, 

 the most northerly runs occurring in late May. In Albemarle Sound, North 

 Carolina's most important shad fishing locality, the earliest shad may appear 

 in February, but the peak of the run occurs in late March or early April. The 

 runs along the entire coast take place when the water temperature in the 

 rivers reaches 50° to 55° F. 



It was formerly thought that the spawning migration originated from the 

 ocean south of Florida, where all shad were believed to spend the winter. As 

 the huge mass moved northward, groups split off to return to the streams of 

 their birth along the coast. This theory is no longer entertained. Although the 

 life of the shad in salt water is still not known, it is believed that the fish 

 move offshore more or less opposite their native streams, and return to their 

 respective sections of the coast or even to their native streams for spawning. 



The shad runs are usually composed of several cycles spaced at intervals 



