Recruitment and hatching dates of grey mullet (Mugil cephalus L.) juveniles in the Tanshui estuary of northwest Taiwan

Ages, growth, and hatching dates of grey mullet Mugil cephalus L. juveniles in the Tanshui estuary of northwestern Taiwan were examined, using growth increments in otoliths of fish collected in November 1995 to March 1996 and November 1996 to March 1997. Growth increments are deposited daily, and were used to determine the ages. Juveniles were composed of multiple cohorts, and their sizes ranged between 17 and 39 mm in total length, corresponding to ages of 29 to 67 d after hatching. The growth rate during the estuarine residency was 0.45 mm d(-1). Hatching dates back-calculated from daily ages were from October to February, which range earlier and later than the spawning period from November to January of a previously known migratory population. This suggests that grey mullet juveniles in the estuary may come from both a resident population and a migratory population, or that there are earlier and later migratory spawning populations.