Mugil Cephalus (Flathead mullet) Sea mullets are particularly abundant in estuaries and coastal waters of southern USA. Reach a maximum length of approximately 22 inches and 4 lbs in weight. The back of the sea mullet may vary in color from Brown to olive green, while the belly is a bright silvery white color. During autumn and winter months, mature mullets school up in estuaries and move to the open sea to commence their annual spawning run. The trigger for this migration is generally associated with the onset of cold northeasterly offshore winds. After spawning, the fish enter rivers to the south of their departure point, moving upstream until the following autumns run. Some other mullet species are fantails, flat-tail mullets and tiger mullets. The large gelatinous eyelid and bluish spot at the base of the pectoral fin best identify the tiger mullets.