NOTE Carlson: Occurrence of neonate and luvenile Charchannus plumbeus in the northeastern Gulf of Mexico 



389 



Results 



Neonate and juvenile sandbar sharks 

 (n = 105) were captured in two areas of 

 the northeastern Gulf of Mexico, Indian 

 Pass, and St. Andrew Sound. Captured 

 sandbar sharks were 572-1640 mm TL 

 (P^ig. 2). Seventeen were determined to 

 be neonates and young-of-the-year 

 (mean size=643 ±44.5 mm TL), as indi- 

 cated by the presence of an open or par- 

 tially healed umbilical scar. The larg- 

 est sandbar shark with a partially 

 healed umbilical scar was 720 mm TL. 

 Following the age-length relationship 

 provided in Sminkey and Musick ( 1995 ) 

 and the life history stage classification in 

 Cortes (in press) we estimated that 52 

 sharks were small juveniles ( about 1-3 

 yr old), 34 were large juveniles (about 4- 

 9 yr old), and 2 were subadults (about 10- 

 12 yr old). Mature adults were not caught. 



Sandbar sharks were captured in all 

 years except 1995 (Fig. 3). The number 

 of individuals collected was highest in 

 1993. Small juveniles were the domi- 

 nant life stage captured in 1993 and 

 1997 and larger juveniles in 1994. 

 Young-of-the-year, including neonates, 

 were caught in all years sandbar sharks 

 were captured. 



The abundance and size of sharks 

 varied with season (Fig. 4). Sandbar 

 sharks were not captured until April 

 when the water temperature approached 

 22°C. These were mostly small juveniles 

 ranging in size fi-om 800 to 1200 mm TL. 

 Neonates were first captured in June 

 when temperatures reached 25°C and 

 young-of-the-year continued to be 

 caught through October. 



There was a significant relationship 

 between abundance and water tempera- 

 ture (r-=0.25, P=0.008), but not with 

 salinity or turbidity (P>0.05). Sandbar 

 sharks were most abundant during 

 summer months when all size classes 

 were caught. Few larger juveniles were 

 caught in fall. 



30. 



25 



20- 



I - 



10. 



i 



i 



ji 



i 



Young-of-the-Year 



Q Small juveniles 



□ Largejuveniles 



 Subadults 



^ 



500 600 700 800 900 1,000 1.100 1,200 1,300 1.400 1,500 1.600 

 Total length (mm) 



Figure 2 



Length-frequency distribution of all sandbar sharks (n = 105) by life his- 

 tory stage caught in gill nets and longlines from October 1992 to October 

 1997. Young-of-the-year includes neonates. 



Z 



rv^ 



[3 Young-of-the-year 



Q Small juveniles 



D Largejuveniles 



 Subadults 



I 



1992 



1993 



1994 1995 



Year 



1996 



1997 



Figure 3 



Overall abundance of sandbar sharks captured by year and life history stage 

 from October 1992 to October 1997. Young-of-the-year includes neonates. 



Discussion 



Presence of neonate and juvenile sandbar sharks in 

 the northeastern Gulf of Mexico suggests that sand- 



bar sharks pup in the eastern Gulf of Mexico. Springer 

 (1960) proposed the existence of two breeding popula- 

 tions of sandbar sharks, one off the mid-Atlantic coast 



