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

Abstract

Daily commercial fishing data were used to determine the relative abundance of the shovelnose guitarfish Rhinobatos productus (Ayres, 1856) in Bahia Almejas, Baja California Sur (Mexico), from August 1991 to December 1995. Data suggest that seasonal trends exist in the catch, with maximum values from May to August. In order to determine if the seasonality is a result of variations in the abundance, catch effort data (number of nets laid) were included 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 behavior of R. productus abundance follows lunar cycles, sea temperature and probably food availability, all critical factors if we consider that the species 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 even years.