FISHERY BULLETIN: VOL. 70, NO. 3 



1969-1971).* Their distribution in time and 

 space corresponds closely to the position of the 

 13° to 18°C isotherms. Six of these charts are 

 presented in Figure 2. 



In July. August, and September, the 13° to 

 18°C isotherms are situated in the Gulf of Maine 

 (Cape Cod to Bay of Fundy) . It was from here 

 that Talbot and Sykes (1958) reported the ma- 

 jority of their recoveries in these months. Re- 

 coveries from the Connecticut River taggings 

 were confined exclusively to this area during 

 July (Figure 2D), August (Figure 2E), and 

 September. In October (Figure 2F), Novem- 

 ber, and December these waters cool and the 13° 

 to 18 °C isotherms move south to the middle At- 

 lantic region, the general area where shad are 

 said to winter (Talbot and Sykes, 1958; Walburg 

 and Nichols, 1967). During these months, as 

 stream temperatures drop below 15.5°C, juvenile 

 shad migrate out of their streams and, as Talbot 

 and Sykes suggested, they probably join the large 

 body of southward migrating adult and imma- 

 ture shad as they pass on their way to the middle 

 Atlantic wintering area. 



In December and January (Figure 2A) , water 

 of appropriate temperature extends in a narrow 

 band near the coast of Florida, and the shad can 

 move into the St. Johns River along the band. 

 In February and March (Figure 2B), 13° to 

 18°C water bathes the coast of the southern At- 

 lantic States from Cape Hatteras south provid- 

 ing access for shad to coastal streams in those 

 States. At this time Connecticut River shad 

 first appear off the coast of North Carolina and 

 Virginia and begin to move north along the coast, 

 mainly within the bounds of the 13° to 18°C iso- 

 therms. During April and May (Figure 2C), 

 shad continue to move north as they follow the 

 movement of the 13° to 18°C isotherms. In 

 April they are located around Chesapeake Bay 

 and Delaware Bay and contribute to the runs 

 into streams in these areas. By May shad are 

 concentrated in the Long Island region and run 

 into the Hudson and Connecticut Rivers. In 



* U.S. Coast Guard Oceanographic Unit. 1969-1971. 

 Monthly temperature charts, July 1969 to December 1971, 

 available U.S. Coast Guard Oceanographic Unit, Air- 

 borne Radiation Thermometer Program, Bldg. 159-E 

 Washington Navy Yard, Washington, D.C. 20390. [Pro- 

 cessed.] 



June there is movement of the isotherms farther 

 north along the coast, corresponding to the peaks 

 of the shad runs in streams to the north. Again 

 in July (Figure 2D), August (Figure 2E), and 

 September, the Gulf of Maine reaches optimum 

 temperature for the species. 



The northern and southern limits of the range 

 of shad on the Atlantic coast appear to be de- 

 fined by the temperature relationship described 

 above. In June and July a narrow tongue of 

 13°C water typically extends to the mouth of the 

 St. Lawrence River, the northern extension of 

 the fish's range. North of the St. Lawrence, the 

 ocean seldom warms above 13°C. In the south 

 shad appear to be blocked from extending their 

 range into the Gulf of Mexico by a band of water 

 south of Cape Kennedy that rarely cools below 

 21 °C even in December and January (U.S. Naval 

 Oceanographic Office, 1967) . It is probable that 

 Alosa alabamae, a closely related species that is 

 native to most principal streams tributary to the 

 Gulf of Mexico east of the Mississippi, evolved 

 from Alosa sapidissima. Prior to the emergence 

 of the Florida peninsula, the range of shad may 

 have included these Gulf rivers. Florida's emer- 

 gence would have produced an efl'ective geologi- 

 cal barrier between the stocks, thereby promot- 

 ing their separate evolution. In this connection 

 we note that a narrow band of water of the tem- 

 perature range 13° to 18°C extends along the 

 northernmost coast of the Gulf of Mexico during 

 the months of December to March (Rivas, 1968) . 



PACIFIC OCEAN MIGRATION OF SHAD 



Prior to 1871 shad occurred only on the east- 

 ern coast of North America. In that year shad 

 from eastern rivers were stocked in the Sacra- 

 mento River. So successful was the venture that 

 by 1880 shad were reported to range from Todos 

 Santos Bay, Baja California, to Kodiak, Alaska 

 (Welander, 1940; Claussen, 1959). Shad make 

 no spawning runs south of San Francisco Bay 

 because there are no streams of sufl[icient size. 

 The Fraser River is thought to be the most north- 

 erly river in which they spawn (Carl, Clemens, 

 and Lindsey, 1967). 



Nothing concrete is known about the migra- 

 tions of the shad in the Pacific Ocean but cir- 



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