MEDVED and MARSHALL: FEEDING AND BIOLOGY OF YOUNG SANDBAR SHARK 



August) both in 1977 and 1978, i.e., unbalanced 

 in 1977 but balanced in 1978. For all study years 

 taken together, the number of male sandbar 

 sharks caught did not differ significantly from 

 the number of females caught during day or night 

 periods, during flood or ebb current periods, at 

 any of the three fishing depths, or for any of the 

 four current speed categories (2-tailed chi-square 

 goodness of fit Test, a = 0.05). 



With the exception of one sandbar shark (137.0 

 cm TL), the catch ranged from 60.0 to 112.5 cm 

 TL. The length distributions for 1977 and 1978 

 are presented in Figure 2. Both distributions 

 were based on relatively small numbers of sand- 

 bar sharks and are no doubt rough approxima- 

 tions of the actual size distributions. The fact that 

 the distributions were not continuous and were 

 characterized by several well-defined peaks does, 

 however, suggest that in both years, the popula- 

 tion of sandbar sharks consisted of relatively dis- 

 tinct size classes. Based on only visual inspection 

 of the distributions, it appears that at least 3 and 

 possibly as many as 5 different size classes may 

 have been present. In general, similar size dis- 

 tributions were found for sex, light, tidal current 

 stage and speed, and fishing depth categories. 



< 



X 

 CO 



O 10. 



z 



1978 



a 



60 65 



1977 



75 80 85 



fl 



95 100 105 110 



TOTAL LENGTH (cm) 



Figure 2. — Frequency distribution for total length of sandbar 

 sharks caught and measured in 1977 and 1978. The total length 

 given for each interval is the beginning length for that 2.5 cm 

 wide interval. 



DISCUSSION 



Despite many hours of fishing, no sandbar 

 sharks were caught before the first week of June 

 either in 1977 or 1978, suggesting they were not 

 present in the area during this time. Local fisher- 

 men who commonly catch numerous sharks in 

 their gill nets also did not encounter sandbar 

 sharks over this period; it appears that few, 

 if any, sandbar sharks had migrated into the 

 Chincoteague Bay area before the first week in 

 June during these years. The consistency in 

 CPUE among months within each year (Table 1) 

 suggests that the abundance of sandbar sharks 

 rem.ained relatively constant in June, July, and 

 August. 



The mean CPUE of 1.02 sandbar sharks/h for 

 the study indicates that the Chincoteague Bay 

 area supports a large number of young sandbar 

 sharks during the summer. The factors respon- 

 sible for yearly differences in CPUE (Table 3) are 

 unknown. Because fishing locations and times 

 were selected in a random fashion and fishing 

 technique was standardized over the entire 

 study, it is unlikely that the differences were a 

 result of the methods employed. Year-to-year 



changes in population numbers and /or shifts 

 in distribution resulting in local differences in 

 abundance may have been involved. 



The significantly higher CPUE experienced 

 during the night (Table 4) may relate to day- 

 night differences in 1) the abundance of sandbar 

 sharks in Chincoteague Bay, 2) the availability of 

 prey, 3) the visual "attractiveness" of the bait, or 

 4) the feeding activity of young sandbar sharks. 



Movements of sandbar sharks out of Chinco- 

 teague Bay to adjacent ocean waters during the 

 day and back into the bay during the night could 

 result in the observed differences. The move- 

 ments of 23 sandbar sharks tracked in this 

 area (Medved unpubl. data) were strongly ori- 

 ented in the direction of tidal current flow and do 

 not suggest a day-night pattern of movement into 

 and out of the bay. 



A decrease in the availability of various prey 

 species could also account for increased CPUE 

 during the night. Observations confirmed by local 

 crab fishermen indicate that the blue crab (the 

 most common food item found in the stomachs 

 examined) is frequently found swimming near the 

 water's surface during the night but rarely during 



445 



