391 



Abstract— Tho goal of our study was 

 to iiiulerstand the spatial and tempo- 

 ral variation in spawning and settle- 

 ment of gray snapper (/^i/(/«;i(/s^'n.sc'i/s) 

 along the West Florida shelf (WFS). 

 Juvenile gray snapper were collected 

 over two consecutive years from sea- 

 grass meadows with a benthic scrape 

 and otter trawl. Spawning, settlement, 

 and growth patterns were compared 

 across three sampling regions (Pan- 

 handle, Big bend, and Southwest) by 

 using otolith microstructure. Histology 

 of adult gonads was also used for an 

 independent estimate of spawning time. 

 Daily growth increments were visible 

 in the lapilli of snapper 11-150 mm 

 standard length; ages ranged from 38 to 

 229 days and estimated average plank- 

 tonic larval duration was 25 days. Esti- 

 mated growth rates ranged from 0.60 

 to 1.02 mm/d and did not differ among 

 the three sampling regions, but did 

 differ across sampling years. Back-cal- 

 culated fertilization dates from otoliths 

 indicated that juveniles in the Panhan- 

 dle and Big Bend were mainly summer 

 spawned fish, whereas Southwest juve- 

 niles had winter and summer fertiliza- 

 tion dates. Settlement occurred during 

 summer both years and in the winter 

 of 1997 for the southern portion of the 

 WFS. Moon phase did not appear to 

 be strongly correlated with fertiliza- 

 tion or settlement. Histological samples 

 of gonads from adults collected near 

 the juvenile sampling areas indicated a 

 summer spawning period. 



Temporal and spatial dynamics of spawning, 

 settlement, and growth of gray snapper 

 iLut/anus griseus) from the West Florida shelf 

 as determined from otolith microstructures 



Robert J. Allman 



Southeast Fisheries Science Center 

 National Marine Fisheries Service 

 3500 Delwood Beach Road 

 Panama City, Florida 32408 

 E-mail address Bob Allmanininoaagov 



Churchill B. Grimes 



Southwest Fisheries Science Center 

 National Manne FIshenes Service 

 1 10 Shaffer Road 

 Santa Cruz, California 95060 



Manuscript accepted 21 February 2002. 

 Fish. Bull. 100:391^03 (2002). 



A primary goal of fisheries ecology is 

 to determine the causes of annual vari- 

 ation in recruitment and to predict 

 the number of individuals that reach 

 a harvestable size (Frank and Leggett, 

 1994). This variation can be substan- 

 tial; recruitment to marine fish stocks 

 can vary by one or two orders of mag- 

 nitude (Shepherd and Gushing, 1990). 

 An understanding of recruitment dy- 

 namics remains a critical, unresolved 

 problem in fisheries science (Houde, 

 1987). Improved understanding is vital 

 for better conservation of exploited 

 marine fish populations for it would en- 

 able prediction of future harvests (Woos- 

 ter and Bailey 1987). 



Gray snapper (Lutjanus griseus), 

 also known as mangrove snapper, are 

 found in the western Atlantic and 

 Gulf of Mexico from North Carolina to 

 Bermuda and south to Brazil, Rarely, 

 individuals are recorded as far north as 

 New England (Hoese and Moore, 1977). 

 Adults generally occur offshore in areas 

 associated with coral reefs or other hard 

 bottom substrate. Spawning off Florida 

 is thought to occur from June through 

 September, and individual gray snap- 

 per probably spawn more than once 

 during the spawning season (Starck, 

 1971). Larvae, which are planktonic up 

 to about 10 mm standard length (SL) 

 (Starck, 1971), have been reared in the 

 laboratory and described by Richards 

 and Saksena (1980). Juvenile gray 



snapper are associated with inshore 

 Thalassia beds (Chester and Thayer, 

 1990). Young snapper remain in these 

 Thalassia beds until approximately 80 

 mm SL when they begin to congregate 

 around debris and channel edges. Sex- 

 ual maturity occurs at 175-180 mm or 

 three years of age (Starck, 1971). 



Gray snapper support an important 

 recreational and commercial fishery in 

 the Gulf of Mexico. Commercial land- 

 ings in the Gulf of Mexico, once over 

 900,000 lb in 1983 had declined to less 

 than 430,000 lb by 1997 (Bennett'). 

 Gray snapper are popular among sport 

 fishermen; recreational landings in the 

 Gulf of Mexico for 1997 were estimated 

 at 877,000 lb (U.S. Dep. Commer.2). 



The boundaries of the study area ap- 

 proximately represent the range of sea- 

 grass meadows along the West Florida 

 shelf ( WFS ) ( i.e. St. Andrew Bay is near 

 the northwest extreme and Ft. Myers 

 is near the southwest). The study area 

 also experiences variation in climate, 

 the north portion being warm-temper- 



' Bennett, J. 1998. Automated landings as- 

 sessment for responsive management. Gulf 

 of Mexico Commercial landings for selected 

 species, 87 p. Miami Laboratory, Southeast 

 Fisheries Center, National Marine Fisheries 

 Service, Miami, FL 33149. 



- U.S. Department of Commerce. 1998. Fish- 

 eries of the United States. 1997. Current 

 fishery statistics no. 9700, 156 p. Statistics 

 Div, Rm 12340, 1315 East-West Highway, 

 Silver Spring, MD 20910-3282. 



