NOTE Burton et al.: Spawning aggregations of Lut/anus analis at Riley's Hump 



405 



instance of commercial fishing on this area occurred in 

 1968 by a fisherman named Riley. 1 However, the naviga- 

 tion device in common use in 1968 was LORAN (long 

 range navigation) A; thus, the likelihood of a fisherman 

 finding the exact spot where he fished previously was 

 much less likely than with today's global positioning 

 system (GPS) receivers. Large-scale commercial fishing 

 of Riley's Hump began in 1976, with the introduction of 

 the improved LORAN C navigation system. 



Commercial fishermen began fishing the area with 

 longline gear in 1979, and fish traps were introduced 

 there in 1984. This was the period of the most intensive 

 fishing; longliners harvested between 10 and 21 metric 

 tons per trip and fish trappers typically landed an aver- 

 age of 11.5 metric tons (Gladding 1 ). It is necessary to 

 rely on knowledgeable fishermen for anecdotal data such 

 as this because the National Marine Fisheries Service 

 (NMFS) did not separate out individual species in their 

 data sets prior to 1986, instead consolidating all snap- 

 pers into an unclassified snapper category. After 1986, 

 landings from the Dry Tortugas were included with 

 the rest of the Florida Keys in a Monroe County total; 

 therefore it is virtually impossible to obtain an exact 

 magnitude of the landings from the Dry Tortugas for 

 this time frame without information from knowledge- 

 able fishermen who were involved in the fishery at the 

 time. In addition to the commercial effort, a small fleet 

 of headboats ran multiday fishing trips to Riley's Hump 

 and other areas in the Dry Tortugas (Dixon 2 ). 



Fishermen began to realize declining catches in the 

 mid-1980s and brought this to the attention of the fish- 

 ery management councils. The Gulf of Mexico Fishery 

 Management Council (GMFMC) enacted a spawning- 

 season closure in 1992, prohibiting fishing on Riley's 

 Hump in May and June (Gulf of Mexico Fishery Man- 

 agement Council, 1992). An analysis of pre- and postclo- 

 sure commercial landing data revealed that, as a result 

 of the closure, there was a shift in effort to the months 

 on either side of the period of closure, and landings 

 during the two-month closure decreased in only one of 

 the months while annual landings increased (Burton, 

 1997). After further urging by fishermen and an effort 

 by the Tortugas Working Group (a group of stakehold- 

 ers appointed by the Florida Keys National Marine 

 Sanctuary [FKNMS] Advisory Council), the Tortugas 

 South Ecological Reserve (TSER) was created in July 

 2001 specifically to protect the spawning aggregation 

 and habitat of mutton snapper. Current regulations pro- 

 hibit all uses of the reserve, except continuous transit 

 through the reserve, for any vessels without a FKNMS 

 research permit. The authors initiated data collection 

 on Riley's Hump in July 2001 to document the effect of 

 the newly designated ecological reserve on abundance 

 of snappers and groupers. 



1 Gladding, P. 2003. Personal commun. 27A 12 th Avenue, 

 Stock Island, FL 33040. 



2 Dixon, R. 2003. Personal commun. CCFHR, NMFS, 

 NOAA, 101 Pivers Island Rd., Beaufort, NC 28516-9722. 



Materials and Methods 



Study area 



Riley's Hump is a carbonate bank of Holocene origin 

 located 20 km southwest of the Dry Tortugas National 

 Park (DTNP) island of Garden Key (Ft. Jefferson). Riley's 

 Hump sits in the northeast corner of the TSER within 

 the FKNMS (Fig. 1). The area has a predominantly 

 low-relief hardbottom and patchy hard coral and scat- 

 tered gorgonian sponge-soft coral communities. Rising 

 to within 30 m of the surface, Riley's Hump covers an 

 area of approximately 10 km 2 . Habitat mapping efforts 

 by Franklin et al. (2000), who used a nine-tier habi- 

 tat classification scheme, and visual observations from 

 SCUBA dives revealed that Riley's Hump consisted 

 mostly of areas of rocky outcropping and some patchy 

 hard bottom in sand. More detailed multibeam mapping 

 showed that the top of the bank is relatively flat and has 

 an escarpment on the south side of the bank dropping 

 from 30 m to well over 50 m deep (Fig. 2) (Mallinson 

 et al., 2003). 



Sampling 



Initial sampling stations were selected in 2001 by divid- 

 ing the top of Riley's Hump into a grid consisting of 

 0.40-km 2 sections and by conducting a census with the 

 ship's depth sounder in order to identify (within as many 

 grids as possible) reef habitat that could be reached by 

 dives. Ten initial stations were selected according to this 

 procedure. Five more stations were added in 2002 at the 

 recommendation of our vessel captain, Peter Gladding 

 (Fig. 2). Two-man dive teams conducted several 30-m 

 visual census strip transects (Brock, 1954) at each sta- 

 tion during the summer months of each year, enumerat- 

 ing all species of snappers and groupers observed. 



Results 



We summarize our observations of mutton snapper abun- 

 dance and behavior on Riley's Hump in Table 1, along 

 with the observation's relation in time to the lunar cal- 

 endar. The initial sighting of an unusually large group 

 of mutton snapper occurred on 17 July 2001. A group 

 of 10 fish was observed by the senior author at station 

 2 (Fig. 2). The fish were swimming 0.5-1 m apart in 

 a group approximately 1.5 m above the seafloor. The 

 next year, on 27 May 2002, we observed a larger group 

 of approximately 75-100 mutton snapper on the same 

 site, station 2 (Fig. 2). These fish were exhibiting simi- 

 lar behavior to that observed the preceding year. The 

 group remained schooled while the dive team completed 

 one 30-m visual transect and then slowly dispersed as 

 the divers returned to the aggregation location. On 15 

 June 2003, a team of divers discovered an aggregation 

 of over 200 individual mutton snapper at station 12 

 (Fig 2). The fish repeatedly swam up to the diver doing 

 the census transects and then slowly turned and swam 



