WITHIN-SEASON DIFFERENCES IN GROWTH OF 

 LARVAL ATLANTIC HERRING, CLUPEA HARENGUS HARENGUS 



Cynthia Jones' 



ABSTRACT 



Data (il)laitic'il from two previous studies of larval Atlantic herrinj^ Kff'Wth were compared, based on otolith 

 intremeiU estimated age. These data, from the Gulf of Maine in 1976-77 and 1978-79, supported the 

 hypothesis that larvae hatched early in the spawning season grew faster than larvae hatched late. Differ- 

 ences were siffnificant under assumptions that increments were deposited in the otolith either daily or at 0.5 

 increments per day. Corroborative evidence indicated that otolith increments were formed daily at least dur- 

 in.u; the early part of the spawning season. 



The otolith increment technique has been used to 

 estimate age and growth in field-caught larval Atlan- 

 tic herring, Clupea harengus harengus, in the Gulf of 

 Maine by Townsend and Graham (1981) and by 

 Lough et al. (1982). Use of the increment technique 

 to estimate age usually assumes daily deposition of 

 otolith increments. Uncertainty exists, however, 

 regarding increment deposition rates in the otoliths 

 of larval herring. Gjosaeter (1981) and 0iestad 

 (1982) have observed daily increment deposition. In 

 contrast, Geffen (1982) found that increment deposi- 

 tion can be variable and a function of growth rate in 

 larval herring, underscoring the problem in simply 

 assuming that increments occur daily under field 

 conditions. Growth calculations based on assump- 

 tions of daily increment deposition in populations 

 that experience variable increment deposition rate 

 would result in inaccurate estimates of growth rates. 

 In most cases where otolith increment deposition has 

 been tested under suboptimal conditions, the deposi- 

 tion rate has been found to be nondaily (for review 

 see Jones 1984). Estimates of growth rates can be 

 made, however, by expressing growth based on 

 increment counts and with the use of corroborative 

 evidence to determine periodicity of increment 

 deposition. 



Das (1968) found that growth rates of larval Atlan- 

 tic herring, measured by following the progression of 

 length modes over time, were different within a 

 spawning season. He stated that early-spawned lar- 

 vae grew faster than late-spawned larvae and model- 

 ed growth with curvilinear functions. Townsend and 

 Graham (1981) also reported two different growth 



'Graduate School of Oceanography, University of Rhode Island, 

 Kingston. RI 02882-1197; present address: Department of Natural 

 Resources, Fernow Hall, Cornell University, Ithaca, NY 14853. 



rates for Atlantic herring, one for larvae born prior 

 to November 5 and one for larvae born later. Each 

 group was modeled by two regression lines to 

 emphasize that growth ceased in January and resum- 

 ed in February. In their study, early- and late- 

 hatched groups were analyzed separately and the 

 comparison of growth between larvae hatched early 

 versus late in the season was not statistically 

 verified. 



This paper uses otolith increment data from Town- 

 send and Graham (1981) and from Lough et al. 

 (1982) to compare early-season versus late-season 

 larval Atlantic herring growth. The comparisons are 

 made using the assumptions of both daily and non- 

 daily otolith increment deposition. 



METHODS 



Raw data for otolith counts and larval fish lengths 

 used in these studies were obtained from Gregory 

 Lough of the National Marine Fisheries Service, 

 Northeast Fisheries Center, Woods Hole, MA, and 

 from Joseph Graham and David Townsend of the 

 Maine Department of Marine Resources, Boothbay 

 Harbor, ME. Both data sets were used in the detec- 

 tion of within-season differences in growth rates. 

 Although the study of Lough et al. (1982) encom- 

 passed a larger area, only data from the Gulf of 

 Maine were included in the analysis (Table 1), in 

 order that comparisons were made within the same 

 area as for Townsend and Graham (1981). Methods 

 employed for the collection of data were reported by 

 Lough et al. (1982) and by Lough and Bolz (1979) for 

 the 1976-77 data and by Townsend and Graham 

 (1981) for the 1978-79 data. 



For each season (1976-77, 1978-79), data were 

 analyzed in three ways: 



Manuscript accepted October 1984. 

 FISHERY BULLETIN: VOL. 83. No. 3, 1985. 



289 



