MORSE: CATCHABILITY, GROWTH, AND MORTALITY OF LARVAL FISHES 



ratios of day, night, and twilight catches show 

 seasonal or areal differences, separate ratios of 

 the mean catch per 10 m" were calculated for 

 each month for all subareas and by subarea 

 (Table 2). In all months the ratios of night- 

 versus-day catches for all subareas combined 

 were greater than one. Night-to-day ratios 

 ranged from 1.01 in September to 3.23 in Jan- 

 uary and the mean for all months was 1.82 (SD = 

 0.56). The extreme values in January and 

 September may be related to the relatively low 

 sample sizes for these two months; however, the 

 higher catches at night relative to both day and 



twilight catches remained quite consistent 

 regardless of month. 



Considerably more variability in the ratios 

 between months is evident when each subarea is 

 analyzed separately, but the general trend of 

 dominance in night catches is still evident within 

 each subarea. The extraordinarily low ratio for 

 twilight-versus-day catches for January in the 

 Gulf of Maine results from a few extremely high 

 twilight catches and relatively low sampling 

 intensity (A^ = 17). 



Catches of all larvae grouped by water column 

 depth are shown in Figure 2. They peak at 



Table 2. — Ratios of night (N):day (D) and twilight (T):day (D) mean catches of larval 

 fish caught off the northeast United States, 1977-84, by subarea and combined by 

 month, n = number of samples; MAB = Middle Atlantic Bight; SNE = Southern New 

 England; GB = Georges Bank; GOM = Gulf of Maine. 



All 



MAB 



SNE 



GB 



GOM 



RLL LHRVflE BY DEPTH 



D DRY 



 NIGHT 



 TWILIGHT 



DEPTH RHN6E CM) 



Figure 2. — Mean catch of all larvae by bottom depth interval for day, night, and 



twilight. 



421 



