406 



Fishery Bulletin 103(2) 



Loggerhead Key /■ 



Middle Key 



Garden Key 



Bush Key 



Riley's Hump 



South Tortugas Ecological Reserve 



12 Miles 



Figure 1 



Location of Riley's Hump, Tortugas South Ecological Reserve, Florida 

 Keys National Marine Sanctuary. 



away. The aggregation was spread out over a wide area, 

 was not as dense as in the previous two sightings, and 

 exhibited the milling behavior similar to that described 

 by Thresher (1984) for several other species of lutjanids. 

 This aggregation remained at the site throughout the 

 entire 20-minute census dive. Later that day, divers 

 recording their observations at nearby station 2 reported 

 a group of approximately 100 mutton snapper. These fish 

 were more widely dispersed and maintained a distance 

 of 3-5 m from divers. Finally, on 4 July 2004, the senior 

 author and another diver encountered a large school 

 of approximately 300 mutton snapper at station 12, 

 exhibiting behavior similar to that observed during the 

 preceding year. 



Discussion 



We believe that the large groups of fish encountered at 

 station 12 in June 2003 and again in July 2004 were 

 spawning aggregations based on their behavior and 

 on the timing and location of the aggregation. First, 

 behavior of the snappers themselves was not typical 

 of nonspawning individuals. Although Humann (1997) 

 described them as being very curious, mutton snapper 

 are typically described as solitary animals (Domeier 

 and Colin, 1997), cautious of divers, and not allowing 

 close approach. Many large reef fishes exhibit simi- 

 lar solitary behavior, such as Nassau grouper (Smith, 

 1972) and black grouper (Eklund et al., 2000). The 



