Seasonal and geographical variation of the mating call of the oyster toadfish Opsanus tau L.

The boatwhistle, the mating call of the oyster toadfish Opsanus tau L. undergoes a pronounced seasonal cycle. The fundamental frequency increases to a peak early in the summer and then decreases markedly in the middle of July. The call duration decreases coincident with the fundamental frequency. It is hypothesized that these fluctuations are controlled by hormonal factors although temperature exerts a direct effect on the fundamental frequency.The fundamental frequency of the boatwhistle in early season is higher in southern populations than in northern ones. Part of this increase is attributed to increased temperature of southern waters. Call duration, which is independent of temperature, varies irregularly up and down the coast.