GRAHAM, CHENOWETH, and DAVIS: LARVAL HERRING 



captured larvae were also highest in the autumn, 

 lowest in the winter with an increase in the 

 spring. The timing of autumnal abundance 

 varied between years and will be discussed in 

 detail in the section on movements. As recorded 

 by Graham and Boyar (1965) the Sheepscot 

 estuary usually contained more larvae than the 

 Damariscotta estuary. About 60-68% of the 

 total catch was taken in the Sheepscot in a given 

 year. 



Seasonal changes in the dispersal of larvae 

 were analogous to those of abundance. Larvae 

 were aggregated in the autumn and spring and 

 dispersed in the winter. For instance, catches 

 during an autumn cruise had a coefficient of var- 

 iation of 214%, during a winter cruise 17%, and 

 during a spring cruise, 50%. Exploratory 

 cruises showed that larvae were dispersed from 

 the headlands to 28 km up the estuaries in the 

 Boothbay area during early March when vv^inter 

 conditions still prevailed. 



Changes in distribution occurred in the au- 

 tumn and spring when the larvae moved land- 

 ward. These changes were apparent when the 

 average catch rates from the Boothbay area (x 

 Boothbay) were compared synoptically with 

 those from cruises in the adjacent coastal area 

 from Cape Small to Penobscot Bay (x coastal). 

 The synoptic catch rate from the Boothbay area 

 was obtained by interpolating between rates of 

 the biweekly cruises that occurred a few days 

 before and after a given coastal cruise. The 

 percentage catch rate of larvae in the Boothbay 

 area [x Boothbay /x Boothbay + x coastal)] X 

 100 did not exceed 40% during October when 

 hatching was at its peak, then reached almost 

 90% in November coincident with a decline in 

 hatching (Figure 3) . The percentage was again 

 low in February and March, but increased to 

 about 85% in April and May prior to metamor- 

 phosis. Similar comparisons between Boothbay 

 data and those from coastal areas east and west 

 of Boothbay did not yield these relations. Ap- 

 parently, the shoreward shift in distribution was 

 not synchronized along the entire coast. 



Other movements of larvae were evident from 

 an analysis of the data from the coastal and 

 Boothbay areas. In autumn, an alongshore 

 movement from east to west was apparent when 



< 





I 



< 



OCT. 



NOV. DEC. JAN. FEB. MAR. APR. 



MAY 



Figure 3. — The change in percentage in the average 

 catch rate in the Boothbay area as compared with the 

 average catch rate in the coastal area. 



larvae were obtained in the Boothbay area that 

 were larger than those recently hatched in the 

 western coastal sector. The movement of larvae 

 in the spring was marked by their accumulations 

 in locations receiving shoreward intrusions of 

 coastal water and by the relation of their dis- 

 tribution with that of surface salinity. The in- 

 trusions resulted from eddies formed by the spa- 

 cing of river discharge along the western sector 

 of the coast (feathered arrows, Figure 4) . The 

 configurations of isohalines and lines of equal 

 larval density throughout the coast were often 

 similar. Such similarity indicated that the mag- 

 nitude of station-to-station differences in catch 

 paralleled the station-to-station differences in 

 salinity. These differences were accumulated for 

 coastal stations from west to east and their fre- 

 quency distributions were plotted on probability 

 paper for two cruises having widely different 

 salinity distributions (Figure 5). The cumula- 

 tive frequencies of salinity and catch were alike 

 for a given cruise, but differed between cruises. 

 We infer from these results that the larvae are 

 carried by currents, indicated by the station-to- 

 station differences in salinity. The precise di- 

 rection of drift cannot be ascertained because it 

 is not possible to determine whether the salinity 

 distribution is causing the current or is the 

 effect of the current, perhaps generated by 

 winds. 



3U 



