Evidence of billfish reproduction in the southern Gulf of California, Mexico

Billfish reproduction at the entrance of the Gulf of California was investigated by examining 8361 billfish sampled from January 1990 to December 2004 to determine reproductive state. Ripe striped marlin Tetrapturus audax (Philippi, 1887) were found from May through December, while mature sailfish Istiophorus platypterus (Shaw in Shaw and Nodder, 1792) occurred from July through November. Gonadal indices showed progressive maturation in striped marlin with the highest indices occurring during the summer. Sailfish showed a steep increase in gonadal indices from July through September, coinciding with minimum catch per unit effort values. An analysis of 275 plankton samples collected during 12 larval research cruises yielded 76 striped marlin and seven sailfish larvae. Larvae were found during June, July, August, September, and November when sea surface temperatures ranged from 27.5 to 31.5°C. With the exception of a 30.5 mm striped marlin early juvenile (August 1992), larval sizes ranged from 2.8 to 7.0 mm.