FISHERY BULLETIN: VOL. 70. NO. 3 



Table 6.— Water temperatures (°C) associated with the 

 peak of the shad run and lower and upper temperatures 

 associated with the middle 90% of the shad caught by 

 anglers at Enfield, Conn. 



Table 7. — Water temperatures and counts per hour of 

 downstream migrating juvenile shad at Matamoras, Pa., 

 September and October 1951. (From Sykes and Lehman, 

 1957.) 



As these data clearly show, the timing of shad 

 spawning migrations is highly correlated with 

 specific water temperatures in all three of the 

 rivers studied. Most shad entered these rivers 

 when temperatures were between 10.0° and 

 15.0°C, even though this required considerable 

 variation in the timing of shad to changing tem- 

 perature conditions in the three rivers. In the 

 St. Johns River (Fla.), water temperatures sel- 

 dom fall below 14.0°C, and the spawning run oc- 



curs at about the seasonal temperature minimum 

 in January. These Florida shad must begin to 

 enter the river during conditions of declining 

 water temperatures, as opposed to the shad from 

 the York and Connecticut Rivers which begin 

 their migrations as temperatures are increasing 

 above an apparent lower limit of 4.0 °C. In Flor- 

 ida, most of the migration occurs while river 

 temperatures are below 20.0 °C. Maximum 

 movements of shad into the York and Connecti- 

 cut Rivers occur at temperatures of about 15.0°C. 

 The sporadic nature of fishing eflfort late in the 

 runs when temperatures were higher probably 

 leads to an underestimate of temperatures, but 

 in all three rivers the mean weekly catch at 19.0° 

 to 21 °C was approximately one-half that re- 

 corded at 13.0° to 15.0°C. 



TIMING OF OUTMIGRATION OF 



JUVENILES RELATED TO STREAM 



TEMPERATURE 



Juvenile shad normally spend their first sum- 

 mer in the river in which they were spawned. 

 They begin to move downstream to the sea in 

 the fall. This migration, too, is apparently trig- 

 gered by temperature. Sykes and Lehman 

 (1957) provided the interesting quantitative 

 data in Table 7. The largest number of shad 

 moved downstream when the temperature 

 dropped below 15.5°C for a period of several 

 days. Similar findings were reported by Smith 

 (1899), Walburg and Nichols (1967), and Chit- 

 tenden (1969). 



OCEANIC WATER TEMPERATURES 



ASSOCIATED WITH SHAD 



MIGRATIONS 



Talbot and Sykes (1958) were the first to de- 

 scribe the oceanic migrations of shad. From 19 

 years of tagging by the U.S. Fish and Wildlife 

 Service, they learned that shad from all the ma- 

 jor Atlantic coast rivers congregate in the Gulf 

 of Maine in the summer and fall. This group of 

 shad includes immature fish from all streams 

 and survivors of spawning from streams north 

 of Chesapeake Bay. South of Chesapeake Bay 

 there are no survivors after spawning. Talbot 



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