Spectrum analysis and least squares fitting to the monthly data (landings) of six demersal species caught by the bottom trawl fleet off Mallorca (Balearic Islands, western Mediterranean) during the period from 1965 to 2008. The best fit to the data is shown superimposed on the landings: an exponential function for the series 1965–1980, and a sinusoidal function for 1980–2008. The periodicity of the oscillations (in months) found in this last period is also shown for each species.