LEGGETT and WHITNEY : WATER TEMPERATURE AND SHAD MIGRATIONS 



F M A M 

 MONTH 



Figure 1. — Shad catches at various temperatures in 

 three Atlantic coast rivers. (A) St. Johns River, Fla.— 

 temperatures are averages, 1960-1967; shad catches in 

 pounds are from weekly catches of the Morris Crab 

 Company, 1962-1967. (B) York River, Va.— tempera- 

 tures are averages, 1953-1962; shad catches are num- 

 bers per net day, 1953-1956 (Massmann and Pacheco, 

 1957). (C) Connecticut River, Conn. — temperatures 

 are averages, 1958-1969; shad catches are numbers per 

 net day, 1944-1964 (courtesy Angelo Baldi) and 1965- 

 1969 (Leggett, 1969). 



ure 1. Few, if any, shad entered the York River 

 until late January when river temperatures ex- 

 ceeded 4.0°C, and peak numbers were captured 

 in April at temperatures around 14°C. At high- 

 er temperatures catches declined. 



For the Connecticut River the mean catch of 

 shad per net day, by weekly intervals, April 1 

 to June 15, was estimated from the daily catch 

 records of commercial fisherman Angelo Baldi 

 for the period 1944 to 1964, and from the daily 

 records of shad captured for tagging by biolo- 

 gists of the Essex Marine Laboratory from 1965 

 to 1969. These data are presented in Figure 1, 

 together with mean weekly river temperatures 



developed from daily water temperature records 

 of the Hartford Electric Light Company, and 

 Essex Marine Laboratory for the period 1958 

 to 1969. Shad are generally soft-bodied and of 

 little economic value after mid-June ; from then 

 on fishing effort is much reduced and is more 

 sporadic. For this reason, the histogram of 

 mean weekly catch was terminated in mid-June. 

 Shad first entered the Connecticut River from 

 late March to early April when water temper- 

 atures ranged from 4.0° to 6.0°C. The mean 

 weekly catch increased with temperature until 

 mid-May when temperatures averaged about 

 15 °C. Catches declined steadily at higher tem- 

 peratures. During the period for which accurate 

 daily temperature records were available, 1958 

 to 1969, the mean temperature at which the peak 

 catch was obtained at the mouth of the river 

 was 13.0°C (Table 5). In 10 out of 12 of those 

 years, the peak catch occurred at temperatures 

 between 11.0° and 15.5°C. In the Connecticut 

 River, a large sport fishery for shad operates at 

 Enfield, in the area 88 to 109 km from the river 

 mouth. A daily record of the number of anglers 

 and the number of shad caught in a State-con- 

 trolled fishing area has been maintained since 

 1942. A daily record of the water temperature 

 at the fishing area has also been kept. Most 

 shad were caught by angling at temperatures 

 ranging from 11° to 18°C (Table 6). On the 

 average, the peak occurred near 15°C. As noted 

 previously, the temperature of peak shad pas- 

 sage at Holyoke, 29 km farther upriver, occurred 

 at temperatures averaging 19.5°C and ranging 

 from 16.5° to 21.5°C. 



Table 5. — Water temperature (°C) associated with peak 

 of shad catch and upper and lower temperatures asso- 

 ciated with middle 90% of the catch at Saybrook, Conn. 



663 



