GROWTH AND AGE STRUCTURE OF LARVAL ATLANTIC HERRING, 



CLUPEA HARENGUS HARENGUS, IN THE SHEEPSCOT RIVER ESTUARY, 



MAINE, AS DETERMINED BY DAILY GROWTH INCREMENTS IN OTOLITHS^ 



David W. Townsend^ and Joseph J. Graham'' 



ABSTRACT 



Larval Atlantic herring, Clupea harengus harengus, were sampled in the Sheepscot River estuary, 

 Maine, using both towed, and buoyed and anchored plankton nets from October 1978 to March 1979, to 

 determine growth rates and age structure. Larval densities and length-frequency distributions, de- 

 termined from the buoyed and anchored net samples, and the ages of larvae captured in the towed nets, 

 as determined by daily growth increments in the otoliths, showed that there were at least two normally 

 distributed age-groups of larvae which entered the estuary in November and December The two 

 groups hatched during early October and late November, and each appeared in the estuary when about 

 4 weeks old. Each of the two age-groups of larvae experienced a reduction in growth rate during the 

 latter half of January and early February. The older of the two groups grew approximately 2.1 mm per 

 week from October to early January and from late February to early March. These older larvae grew 

 little if any, during the midwinter period. The younger of the two groups of larvae showed a similar 

 reduction in growth rate during midwinter and grew about 2.0 mm per week before and about 1.5 nmi 

 per week after this period. 



Research on larval Atlantic herring, Clupea 

 harengus harengus Linnaeus, has been conducted 

 extensively in the western North Atlantic in re- 

 cent years. This has resulted in numerous ac- 

 counts of the abundance and distribution of the 

 larvae, as well as estimates of the generalized 

 growth rates. The growth of Atlantic herring lar- 

 vae in the Gulf of Maine-Bay of Fundy areas has 

 been reported by Tibbo et al. (1958), Tibbo and 

 Legare (1960), Das (1968, 1972), Sameoto (1972), 

 Graham et al. (1972), and Boyar et al. (1973). 

 These workers used the length-frequency method 

 to determine average growth rates of the larvae. 

 Various studies on the seasonal abundance and 

 size distribution of Atlantic herring larvae have 

 shown that in some years there may be more than 

 one mode in the length-frequency distribution for 

 a particular time and geographical area (Tibbo et 

 al. 1958; Tibbo and Legare 1960; Das 1968, 1972; 

 Graham et al. 1972; Boyar et al. 1973; Graham in 

 press), indicating multiple spawnings. These poly- 

 modal length -frequency distributions of Atlantic 

 herring larvae complicate growth rate estimates 



'Ira C. Darling Center Contribution No. 149. 



^Department of Oceanography, University of Maine at Orono, 

 Ira C. Darling Center, Walpole, ME 04573." 



^Department of Marine Resources, Fisheries Research Labo- 

 ratory, West Boothbay Harbor, ME 04575. 



since an individual sample may not represent a 

 single homogeneous group of larvae. 



A relatively new technique for studying the 

 growth of larval fishes was introduced by Pan- 

 nella (1971, 1974). He observed daily growth incre- 

 ments in the otoliths of some tropical and low- 

 temperature adult fishes. Brothers et al. (1976) 

 and Struhsaker and Uchiyama (1976) verified the 

 daily nature of these growth increments in several 

 species of larval fishes. Subsequently, others ap- 

 plied this technique to age and growth studies 

 (Ralston 1976; Taubert and Coble 1977; Barkman 

 1978). Rosenberg and Lough"* used otoliths to age 

 larval Atlantic herring from Georges Bank. The 

 purpose of our study was to use the otolith aging 

 technique to investigate the growth of Atlantic 

 herring larvae in the Sheepscot River estuary of 

 Maine and to examine the age structure of the 

 larvae entering the estuary. 



METHODS 



Larval herring were sampled in the Sheepscot 

 River estuary of Maine using both towed, and 



"Rosenberg, A. S., and R. G. Lough. 1977. A preliminary 

 report on the age and growth of larval herring ( Clupea harengus 



L.) from daily growth increments in otoliths. 

 1977/L:26. 



Manuscript accepted August 1980. 

 FISHERY BULLETIN: VOL. 79, NO. 1, 1981. 



ICES CM. 



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