400 



Fishery Bulletin 100(3) 



virtual population analysis from fishery-dependent data. 

 However, before these data can be used reliably there 

 must be a demonstrated relationship between juvenile 

 abundance and year-class strength. 



Age and growth 



Because of the strong linear relationship between otolith 

 size and fish size and the regression of increments depos- 

 ited after alizarin marks on days after marking, we did 

 not reject the hypothesis that one increment was depos- 

 ited daily. In addition, Ahrenholz (2000) found no signifi- 

 cant difference from 1 increment/d deposited from lapilli 

 of alizarin-marked juvenile gray snapper Juvenile con- 

 generic red snapper (Lutjanus campechaniis) have also 

 been shown to deposit daily increments above a minimum 

 growth rate (i.e. >0.3 mm/d FL) (Szedlmayer, 1998). 



The daily growth rate for juveniles varied between sam- 

 pling years (1 mm/d in 1996 and 0.6 mm/d in 1997) and 

 was similar to growth rates for juvenile red snapper (0.54— 

 0.86 mm/d, Szedlmayer and Conti, 1999). The difference 

 in growth between years could be explained by the fact 

 that most juveniles collected in 1997 were winter-spawned 

 fish collected from SW Florida that may have experienced 

 lower temperatures and that initially had a slower growth 

 rate. Variability in the growth of larval and juvenile fish 

 has been linked to water temperature in many species 

 (Lang et al., 1994; Nixon and Jones, 1997). However, when 

 the same size range of juveniles was compared between 

 regions, there was no significant difference in growth rate. 

 Similarly there was no difference in regional growth rate 

 of co-occurring juvenile gag from the west Florida shelf 

 (Fitzhugh-'). 



Fertilization-date distribution 



All indicators of the temporal distribution of spawning 

 (i.e. juvenile otoliths, oocyte diameter, and histological 

 stage of gonads) indicated peaks in spawning from May 

 until August and a dominant peak in mid-July Very few 

 gray snapper gonads were collected during the winter 

 months in 1996 and none in 1997 because the majority 

 of gray snapper are landed in July and August (U.S. Dep. 

 Commer.'') when they aggregate on offshore reefs to spawn 

 and are probably easier to catch (Starck, 1971; Domeier et 

 al., 1996; Domeier and Colin, 1997). Spawning time has 

 been related to both increasing water temperature and 

 photoperiod for other lutjanids (Arnold et al., 1978; Grimes 

 and Huntsman. 1980). 



No obvious temporal differences were observed in repro- 

 ductive development between regions from adult gonads; 

 however, we determined winter back-calculated fertiliza- 



■' Fitzhugh, G. F. 2000. Unpubl. data. National Marine Fish- 

 eries Service, 3.500 Delwood Beach Road, Panama City, Florida 

 32408. 



■^ U.S. Department of Commerce. 1998. Fisheries of the United 

 States, 1997. Current fishery statistics no. 9700, 1.56 p. Sta- 

 tistics Division, Rm. 12340, 1315 East-West Highway, Silver 

 Spring, MD 20910-3282. 



tion dates for the most southerly part of the sampling 

 region in 1997. In contrast, Domeier et al. (1996) back- 

 calculated spawning dates from June through September 

 using the otoliths from juvenile gray snapper collected 

 from south Florida. Gray snapper larvae have a relatively 

 long pelagic stage of 25 days. The possibility exists that 

 winter-spawned fish were produced from outside the Gulf 

 of Mexico, perhaps from a nearby insular population, and 

 transported from there to settle along the southwestern 

 part of the Florida shelf The view that winter-spawned 

 fish were Gulf of Mexico expatriates is supported by 

 Grimes's (1987) review of lutjanid reproduction. He found 

 two patterns: 1 ) continental populations, with extended 

 summer spawning periods; and 2) insular populations, 

 which spawned year-round with pulses in the spring and 

 fall. However, Domeier et al. (1996) suggested after field 

 observations that snapper spawning patterns are species 

 specific, as opposed to habitat dependent. We collected 

 winter-spawned juveniles in only one of the two years of 

 sampling; therefore it is unknown how frequently expatri- 

 ate settlement events occur and what their importance to 

 gray snapper recruitment might be. 



We could not conclusively demonstrate that spawning 

 occurs in association with lunar cycle peaks. Fertilization 

 date hind-cast from otoliths in 1996 were only marginally 

 associated with a lunar cycle and no relationship was evi- 

 dent in 1997 data. Similarly gonad stage data from adult 

 gray snapper did not reveal any lunar pattern. However, 

 the association of spawning with the lunar cycle has been 

 reported for congeneric species, as well as other conspecific 

 populations. Domeier et al. ( 1996) used a GSI to determine 

 that gray snapper spawning peaked around the time of 

 the new and full moon. Upon examination of adult gonads, 

 Starck (1971) speculated that gray snapper spawned dur- 

 ing or near the full moon. The congeneric species Lutjanus 

 vaigiensis spawned about the time of the full moon (Ran- 

 dall and Brock, 1960) and Lutjanus kasmira spawned dur- 

 ing both new and full moons in the laboratory (Suzuki and 

 Hioki, 1979). 



Larval duration 



Presumed settlement marks were noted in many (60%) of 

 the ageable otoliths, and they were similar in appearance 

 to those observed for several other reef fish species ( Broth- 

 ers and McFarland, 1981; Victor, 1982 and 1986; Sponau- 

 gle and Cowen, 1994). Settlement marks are thought to 

 be associated with morphological and ecophysiological 

 changes which occur during the transition from a plank- 

 tonic to a benthic life stage (Brothers and McFarland, 1981; 

 Victor, 1982; Brothers, 1984). Several lines of evidence sug- 

 gest that we correctly identified settlement marks. On 

 average, planktonic duration, or length of the presettle- 

 ment life history phase (i.e. difference between fertilization 

 and settlement dates ) was 25 days for both sampling years. 

 Similarly, Koenig and Domeier^ reported the planktonic 



6 Koenig, C. C, and M. L. Domeier. 1993. Unpubl. data. De- 

 partment of Biological Sciences, The Florida State Univ., Talla- 

 hassee, FL 32306-2043. 



