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Fishery Bulletin 95 ( 1 ), 1997 
conducted involving our ager and several other ex- 
perienced otolith readers who used otoliths collected 
from throughout the Gulf of St. Lawrence (Savard 
and Simoneau 7 ). This study showed a high agree- 
ment between two agers from our laboratory in Que- 
bec (87%) and agers from the southern Gulf of St. 
Lawrence and eastern Newfoundland (75 and 76%, 
respectively) in the assignment of seasonal-spawn- 
ing type from otoliths. 
The actual spawning season of the mature indi- 
viduals was determined from the stage of sexual 
maturity of each individual by using a temporal 
gonadosomatic index model (McQuinn, 1989). This 
model identifies the spawning season by first deter- 
mining the maturity stage from the ratio of the go- 
nad weight to a power function of the total length 
and by relating this state of maturation to the month 
of capture. Although spawning can occur from April 
7 Savard, L., and M. Simoneau. 1983. Lecture comparative 
d’otolithes de hareng et utilisation des stades de maturite 
sexuelle pour l’attribution du groupe reproducteur. Canadian 
Atlantic Fisheries Scientific Advisory Committee (CAFSAC) 
Res. Doc. 83/86, 28 p. Department of Fisheries and Oceans, 
RO. Box 1006, Dartmouth, Nova Scotia, Canada B2Y 4A2. 
to October, the vast majority of spring herring spawn 
in May and June, whereas the autumn herring spawn 
mainly from mid- August to September (Haegele and 
Schweigert, 1985). The date separating the two 
spawning seasons was arbitrarily chosen to be 1 July, 
as relatively little spawning occurs in late June and 
early July (McQuinn, 1989; Cleary et al. 6 ). 
Throughout this paper, a distinction is made be- 
tween the number of rings read from the otoliths and 
the actual age of the fish because age determination 
depends upon whether an individual is assigned as 
a spring spawner or an autumn spawner. Most au- 
tumn-spawning herring (August-November) do not 
produce a winter ring on the otolith in their first year 
of life (Einarsson, 1951; Jakobsson et al., 1969; 
Rosenberg and Palmen, 1982; Hunt et al. 8 ). The for- 
mation of the winter ring takes place between Octo- 
ber and April-May in metamorphosed juveniles 
8 Hunt, J. J., L. S. Parsons, J. E. Watson, and G. H. Winters. 
1973. Report of the herring ageing workshop; St. Andrews, 
New Brunswick, 11-13 December 1972. International Com- 
mission for the Northwest Atlantic Fisheries (ICNAF) Res. Doc. 
73/2, Ser. 2901, 2 p. ICNAF, P.O. Box 638, Dartmouth, Nova 
Scotia, Canada B2Y 3Y9. 
