Calls of the black drum (Pogonias cromis: Sciaenidae): geographical differences in sound production between northern and southern hemisphere populations. 
Because of apparent reproductive isolation between Northern and Southern hemisphere populations of the black drum Pogonius cromis, we tested the hypothesis that advertisement calls from a southern population would differ from known calls of North American populations.  Additionally, we quantified disturbance and advertisement calls, their changes with fish size and sex, not previously examined in this species.  Unlike most sciaenids, both sexes of P. cromis possess robust sonic muscles, and both produce disturbance calls when handled.  However, only males produce an advertisement call used in courtship.  The disturbance call consists of a variable train of short-duration pulses (average 23 ms).  The duration, interpulse interval, and dominant frequency of pulses are similar in males and females and change developmentally: pulse duration and interpulse interval increase and dominant frequency decreases with fish size.  Advertisement calls, recorded in the field and in captivity, are long-duration (average 184 ms) and tonal.  Based on variation in fundamental frequency, which decreases with fish size, field choruses are composed of different-sized individuals.  The duration of advertisement calls, about a third of those from Florida populations, suggests genetic differentiation between northern and southern populations.