PINKARD, Deanna R; SHENKER, Jonathon M: Seasonal variation in density, size, and habitat distribution of juvenile yellowtail snapper (Ocyurus chrysurus) in relation to spawning patterns in the Florida Keys

The yellowtail snapper (Ocyurus chrysurus; Lutjanidae) supports an economically important commercial fishery in Florida and the Caribbean. Despite it’s commercial and recreational value, little is known about the reproductive biology or juvenile population dynamics of this species in the Florida Keys. Thirty adults were collected monthly from January 2001 to January 2002, and measurements of length, body weight, gonad weight, mesenteric fat weight, and egg diameters were recorded. Results indicate low mean gonad index values for males and females from January through March, with an initial increase in April. Mean gonad index values remained high from May through August 2001. Based on preliminary observations, two habitats were chosen to examine juvenile populations. Visual surveys of juveniles took place spring 2001 through winter 2002, tracking densities and sizes along fixed transects on two shallow patch reefs. Six shallow seagrass sites from Key Largo to Summerland Key were monitored in an attempt to locate recruitment sites. The densities of juveniles at patch reefs varied depending on fish size and age. In the spring reefs were dominated by juveniles ranging in length from 7.5- 25.0 cm that presumably recruited the previous summer and fall. Densities of these size classes decreased by the summer. In the summer the most common size class of fish observed was 0.0- 7.5 cm. Newly recruited juveniles were observed in seagrass beds beginning in August 2001. The preliminary results of this study lead to several conclusions: 1) reproduction is seasonal and varies in regards to the number and timing of peaks in gonad index values, and 2) juveniles display ontogenetic shifts in habitat directly related to size.