REPRODUCTION AND EARLY-LIFE HISTORY OF COMMON SNOOK, CENTROPOMUS-UNDECIMALIS (BLOCH), IN FLORIDA

This paper combines published literature and unpublished Florida Depar tment of Environmental Protection (FDEP) data on snook reproduction an d early life history. Published literature originally dealt with fishe ries investigations (1950s) and freshwater culture (1970s) but has exp anded to include marine stock enhancement, spawning, and larval and ju venile ecology. In addition, ongoing FDEP projects provide considerabl e information. Snook are protandric hermaphrodites that probably spawn near river mouths, passes (inlets), and points of land in central and southern Florida estuaries. Females are older and larger than males a t 50% maturity (5 yrs and 500-522 mm SL versus about 2 yrs and 330-348 mm SL) and have group synchronous ovarian development. The spawning s eason is long (approx. April to December or January) and includes mult iple spawnings. Most spawning occurs between May and September. Spring spawning occurs at water temperatures >22 degrees C and salinities >2 7 parts per thousand. Several researchers noted increased spawning act ivity around the times of spring and summer new or full moons. In pres pawning behavior, females are escorted by a number of(usually) smaller males, but actual spawning has not been documented. In the laboratory , eggs averaged 0.70 mm diameter and hatched in 17-18 h at temperature s of 26-29 degrees C and salinities of 28-38 parts per thousand. Newly hatched larvae (1.4-1.5 mm notochord length) spend similar to 2.5 wks in nearshore waters before their arrival at shallow-water nursery sit es. Eggs have been collected during field studies in only one secondar y embayment of lower Tampa Bay, but preflexion larvae have been taken in lower Tampa Bay and just off the beach at Naples. Postflexion larva e have been reported from both coasts of Florida, but only 16 larvae a re listed in published literature. Late-stage larvae recruit to vegeta ted shorelines of quiet, shallow-cater creeks, canals, and lagoons in both low-salinity (riverine) and high-salinity (mangrove swamp and sal t marsh) environments. Early juvenile-stage snook occupy a spatiality restricted microhabitat along shores having limited water movement, mo derate shoreline slopes, and vegetation extending over and/or into the water; as the juveniles grow, their habitat becomes less defined and restricted. Early juveniles (<40 mm SL) feed on copepods and other mic rocrustaceans, but later juveniles (40-50 mm SL) switch to small fish (mainly poeciliids and cyprinodontids) and crustaceans (mainly palaemo nid shrimp). Factors other than fishing regulations that affect surviv al of adult snook include human impacts on habitat quantity and qualit y and natural perturbations such as cold kills and red tides. Some of these same factors may also affect the survival of larval and juvenile snook.