SAVOY AND CRECCO: MORTALITY OF AMERICAN SHAD 



American shad larvae (10-30 mm TL) were sam- 

 pled during daylight hours in the Connecticut River 

 with a 6.1 m plankton bag seine (2.4 m deep, wing 

 and bag mesh of 0.505 mm) and 30 m lead ropes 

 from 15 May to 20 July 1979-84, 1986, and 1987. 

 No larval sampling was conducted in 1985. One seine 

 haul was taken weekly at 8-12 fixed stations located 

 throughout the major spawning areas (Fig. 1). Fur- 

 ther details on sampling and methods of estimating 

 larval abundance from net samples are contained 

 in Crecco et al. (1983). 



Juvenile American shad (40-90 mm TL) were col- 

 lected weekly from 20 July through 15 October 

 1967-87 at 7-14 fixed stations located above and 

 below the Holyoke Dam (Fig. 1) based on weekly and 

 biweekly seine surveys (Scherer 1974; Foote 1976; 

 Marcy 1976; Crecco and Savoy 1984). The annual 



juvenile index of relative abundance (IND() from 

 1967 to 1987 was the mean juvenile catch per seine 

 haul ( ± SE) from all stations and collection dates 

 (Table 2). 



The Timing of 

 Density-Dependent Mortality 



Analysis 



One of the primary objectives of this study was 

 to determine the magnitude and timing of density- 

 dependent mortality for American shad. Peterman 

 (1978, 1982) found that density-dependent mortality 

 for some stocks of the anadromous sockeye salmon, 

 Oiworhynchus nerka, was confined mainly to the 4-5 

 yr oceanic postjuvenile phase. Given that the Ameri- 



STATIONS 

 X - L A RVA L 



0-JUVENILE 



km 1 90 



SUN D ERLU N D 



HATFIELD 



HO LYOK E 



km 140 



X AG AW AM 

 ENFIELD 



Figure 1.— Location of larval and juvenile 

 American shad sampling stations on the Con- 

 necticut River. 



MASS 

 CONN 



WILSON O 



GLASTON BURY 



km 25 

 O SALMON 



RIVER 



DEEP 

 RIVER 



ESSEX 



k m 1 2 



469 



