Rountree and Able: Abundance, growth, and foraging habits of Mustelus cams 



527 



turityt Castro, 1983; Compagno, 1984). A total of 720 

 YOY and 25 subadult (60-80 cm) to adult (80-130 

 cm TL) smooth dogfish were collected (Table 1). A 

 single well-defined size cohort of YOY dominated 

 catches on the basis of data pooled over all years and 

 gears (Table 1; Fig. 2). The smallest individuals (<40 

 cm) collected during May, June, and early July had 

 fresh umbilical scars. Although adults were not abun- 

 dant, they were collected from May to September. 

 Their relative rarity, however, may have been due to 

 gear avoidance, because we frequently observed 

 adults during night flood tides in the shallow bay in 

 the vicinity of Foxboro and Story Island creeks from 

 May to July. Additionally, on several occasions we 

 observed adults that repeatedly came into contact 

 with gill nets without becoming entangled. A few in- 

 termediate-size individuals (60-70 cm TL) were col- 

 lected in June, July, and September. These individu- 

 als appeared to be small subadults from their length 

 at date of capture ( more strikingly, they were far more 

 robust than the YOY and lacked umbilical scars) and 

 were excluded from the growth analysis for the YOY. 

 The occurrence of YOY in the study area was high- 

 ly seasonal. They appeared first in May and appar- 

 ently left the study area by November (Figs. 3 and 

 4). The timing of fall migration out of the estuary 

 was well defined by their absence in weir, gill-net, 

 and trawl samples during November. The first ap- 

 pearance of YOY during the spring, however, was less 

 well defined because of the lack of gill-net sampling 

 during this period, despite their absence in April weir 

 and seine sampling as well as January-April trawl 

 sampling. Young of the year were abundant in weir and 

 seine collections only during June and July (Fig. 3). 



May Jun Jul Aug Sep Oct Nov Dec 



Date 



Figure 4 



Seasonal abundance (CPUE expressed as the mean num- 

 ber per hour per net) of smooth dogfish collected with gill 

 nets set in marsh creeks and in the adjacent shallow bay 

 during 1990. Data are grouped by habitat (top) and tide 

 stage (bottom) for comparison. Vertical lines are ranges. 



In contrast, they were collected regularly in gill-net 

 samples from both the bay shoal and marsh creek 

 sill locations from June through October (Fig. 4). 

 Peak CPUE in gill-net sampling occurred from July 

 to August. Young of the year collected by weir tended 

 to be smaller than those collected by other gears 

 during June-August ( Fig. 2 ). No tagged ( n - 138 ) YOY 

 were recaptured during our sampling; however, two 

 individuals were recaptured off North Carolina the 

 following winter: one inshore near Cape Fear, North 

 Carolina, in December 1990 and a second off the beach 

 at Cape Hatteras, North Carolina, in March 1991. 



Apr May Jun 



Aug Sep 



Figure 3 



Seasonal abundance of smooth dogfish, based on night weir 

 samples pooled from three subtidal marsh creeks (Foxboro, 

 New and Schooner) during 1988 and 1989 (vertical lines 

 represent one standard error about the mean). Smooth 

 dogfish were absent from day weir samples. 



Sex ratio 



Sex ratios of the YOY did not differ significantly from 

 1:1, averaging 51.8 % (standard error [SE]=2.8) fe- 

 males per net check (n=55 net checks with three or 

 more fish). No significant temporal effect on sex ra- 

 tio was observed. 



Growth 



Young of the year exhibited a very rapid growth rate 

 of 1.9 mmTL/day, or 6.0 g/day ( Table 2), and reached 

 550-700 mm TL by the end of October (Fig. 2 ). There 

 was a significant annual affect on growth rates for 

 both length and weight (i.e. the slopes were not ho- 

 mogeneous among years; ANCOVA, P<0. 0001; Table 

 2; Fig. 5). No effect of sex on growth was observed 

 (Table 2; Fig. 5). Because the slopes were heteroge- 

 neous among years, differences in intercepts among 

 years could not be tested; however, a significant dif- 



