LOUGH ET AL.: ACE AND GROWTH OF LARVAL ATLANTIC HERRING 



for all body parts after net-treatment, whereas 

 preservation in ethyl alcohol (80%) did not cause 

 any additional shrinkage in standard length. 

 Townsend and Graham (1981) indicated that 

 frozen herring larvae (27-45 mm TL) may shrink 

 3-4% more than Formalin-preserved larvae. 

 From our experience we find that length mea- 

 surements of frozen larvae can be more variable 

 than those of Formalin-preserved larvae; how- 

 ever, a thorough study has not been made. No 

 correction factor was applied to our field-col- 

 lected frozen larvae because of the uncertainty 

 of time prior to preservation and the effect of 

 freezing on shrinkage. We do not feel that the 

 Gompertz population growth curve fit to the un- 

 corrected field-collected larvae would be signifi- 

 cantly altered with respect to shape compared 

 with corrected data. When a direct comparison is 

 made in this paper between laboratory-reared 

 and field-estimated larval lengths, a shrinkage 

 correction factor applied to the lab data will be 

 specified based on Theilacker's ( 1980) work which 

 probably is adequate for all clupeidlike larvae. 



RESULTS 



Otoliths from 311 herring larvae caught in 

 plankton hauls were processed in this study cov- 

 ering their first 6 mo of life from October 

 through March 1977 (Table 1, Fig. 1). Approxi- 

 mately 58% of the larvae were collected along the 

 western Gulf of Maine, 23% from Nantucket 

 Shoals, and 19% from Georges Bank. ICNAF 

 surveys have never been conducted during the 

 month of January so that there is a gap in time in 

 our collection of larval otolith data from mid- 

 December 1976 to mid-February 1977. The field- 

 collected larvae ranged in length from 11 to 35 

 mm with most of the western Gulf of Maine lar- 

 vae falling into the 11-31 mm size range; the 

 Georges Bank larvae, 19-25 mm; and the Nan- 

 tucket Shoals larvae, 26-35 mm. The number of 

 otolith increments counted from the field-col- 

 lected larvae ranged from 7 to 160. Since we 

 were not able to collect any recently hatched lar- 

 vae <11 mm length for otoliths on these surveys, 

 laboratory-reared larvae had to suffice for the 

 smallest size. 



Laboratory-Reared Larvae 



Hatching of the laboratory-reared larvae 

 occurred over a 5-d period with 50% hatch esti- 

 mated on 28 October 1978 for a mean incubation 



of 11 d. Yolk-sac resorption was estimated to be 

 50% complete 4-5 d after hatching, and 99% com- 

 plete 6 d after hatching. The larvae began 

 actively feeding at yolk-sac resorption and ap- 

 peared to be healthy without any abnormalities 

 throughout the more than 3 wk of rearing. Mor- 

 tality over the first 13 d from hatching averaged 

 12%/d which is considered low. The age of larvae 

 from hatching midpoint with 0-3 increments is 

 given in Table 2 and Figure 3. The first incre- 

 ment appeared on larval otoliths that ranged in 

 age from to 9 d from hatch with a middate of 4.5 

 d which indicates that the first increment is de- 

 posited near the end of yolk-sac resorption. Lar- 

 vae staged according to Doyle (1977) showed a 

 progression of the three substages la-lc over the 

 first 3 d from hatch so that after the third day 

 only remnants of yolk sac remained. 



The second growth increment occurred in lar- 

 vae 6-18+ d old with a middate of 12 d from hatch 

 or 7.5 d from the middate of the first increment 

 formation. The third increment was observed for 

 the first time on a larva 16 d from hatch, but un- 

 fortunately sampling was terminated before the 



Table 2.— Distribution of otolith growth increments, 

 age in days from hatching midpoint, and mean stan- 

 dard length of herring larvae reared in the laboratory 

 at 10°C. 



'Measurements made on larvae preserved in 75% ethyl alcohol 

 Unpreserved mean length of 55 larvae at hatch was 7.66 mm, 

 standard deviation of 58 (Beyer and Laurence 1981). 



UJ 



a 

 o 



2 



DAYS FROM HATCH 



Figure 3. — Otolith increment deposition for herring larvae 

 sampled from 50% hatch through 18 d of rearing in the labora- 

 tory at 10°C. Encircled points represent yolk-sac larvae. Num- 

 bers above points denote numbers of larvae >1. 



191 



