Allman and Grimes: Spawning, settlement, and growth of Lutianus griseus from Ifie West Florida sfielf 



399 



test indicating that the distribution of hinar 

 settlement dates was not sifjnificantly differ- 

 ent from a uniform distribution. The back-cal- 

 culated settlement date distribution for 1997 

 indicated two distinct settlement events. Set- 

 tlement of the first mode began in December of 

 1996, peaked in late winter, and then declined 

 into late spring. All juveniles from the first 

 event were from the Southwest. The second 

 settlement mode was similar to that seen in 

 the 1996 settlement date distribution, begin- 

 ning in late June, peaking in early August, and 

 finally ending in the early fall. The evidence 

 for lunar periodicity in settlement in 1997 was 

 weak: a chi-square test indicated only a mar- 

 ginally significant difference (P<0.10) from a 

 uniform distribution across lunar month for 

 1997 settlement dates. 



Discussion 



Sampling and collection 



# 



isKo 



Sciilcnient mark 



Figure 9 



Photomicrograph (400x) of settlement mark in a lapillus of gray snapper. 



The collection of juvenile gray snapper from 

 June to November in 1996 was consistent with 

 a May-September spawning period found from 

 previous studies in which the reproductive 

 condition of adults collected off South Florida 

 was used (Starck, 1971; Domeier et al., 1996). 

 However, in 1997 juvenile gray snapper were 

 initially collected in April from southwest 

 Florida, indicating a much earlier spawning 

 time. Differences in the timing of the first 

 appearance of juvenile snapper for 1997 could 

 be related to the seasonal cycle of seagrass 

 dieback and regeneration. Thalassia experi- 

 ences leaf die off with temperatures below 

 15°C (Zimmerman and Livingston, 1976). In 

 the northern most part of the sampling region, 

 greater leaf die off and slower growth during 

 the spring would be expected compared with 

 more southerly areas. This would most cer- 

 tainly limit the chances of survival of early 

 settling larvae in the north because of greater 

 predation risk and lower food availability. 



If gray snapper are truly recruitment-lim- 

 ited and if postsettlement mortality is rela- 

 tively constant (Shulman and Ogden, 1987) 

 and individuals do not migrate out of the area 

 during the monitoring period (Robertson et al., 1988), ju- 

 venile abundance would be an effective predictor of adult 

 abundance two to three years later when the adults are 

 entering the fishery. Gag (Mycteroperca microlepis), a spe- 

 cies with a similar early life history to that of the gray 

 snapper, have a low rate of emigration from the seagrass 

 nursery area during summer and a mortality rate of less 

 than 1%/d (Koenig and Coleman, 1998). Johnson and 

 Koenig (in press) found a strong correlation between ju- 

 venile gag abundance in seagrass meadows and year-class 



25 



20 - 



15 



10 



5/5 5/20 6/5 6/20 7/5 7/20 8/5 8/20 9/5 9/20 10/5 



1997 



20 



15 



10 



 Southwest 

 D Panhandle 

 BBig Bend 



LiJjL 



I 



^ n 



12/5 1/5 2/5 3/5 4/5 5/5 6/5 7/5 8/5 9/5 10/5 



Settlement date 



Figure 10 



Settlement-date distribution for 1996 and 1997. 



strength in the fishery several years later. Juvenile indices 

 have been used successfully to document recruitment for 

 a number of temperate fish species and invertebrates. For 

 example, juvenile indices for striped bass were found to ex- 

 plain 83% of the variation in reported landings from 1963 

 to 1983 (Goodyear, 1985). These data for gray snapper 

 could provide a fishery-independent method for forecast- 

 ing size of year classes several years into the future. This 

 would be a valuable addition to stock assessment which 

 typically features age-based hind-casting methods such as 



