Relative abundance of the shovelnose guitarfish Rhinobatos productus (Ayres, 1856) (Pisces : Rhinobatidae) in Bahla Almejas, Baja California Sur, from 1991 to 1995

Daily commercial fishing data were used to determine the relative abundance of the shovelnose guitarfish Rhinobatos productus (Ayres, 1856) in Bahia A lmejas, Baja California Sur (Mexico), from August 1991 to December 1995. Da ta suggest that seasonal trends exist in the catch, with maximum values fro m May to August. In order to determine if the seasonality is a result of va riations in the abundance, catch effort data (number of nets laid) were inc luded in the calculations and the results were expressed in terms of catch per unit effort (CPUE; org/net/week and org/net/month). The cyclical behavi or of R. productus abundance follows lunar cycles, sea temperature and prob ably food availability, all critical factors if we consider that the specie s uses the area for its reproduction. The species enters massively into the bay during one month and leaves in just two weeks. An alternate trend was identified in the relative abundance between years, with the uneven years ( 1993 and 1995) as the abundant ones. The relative abundance of R. productus increased from 1991 to 1995, even with the respective decreases in the eve n years.