Application of an egg production index to determine reproductive period of the brown shrimp Farfantepenaeus californiensis near Agiabampo, Sonora-Sinaloa, Mexico

Using the percentage of mature females as an index, the reproductive period of the brown shrimp, Farfantepenaeus californiensis, off the coast of Sonora in Mexico, has been shown to occur throughout the year with two peaks of mass spawning. The objective of this study is to determine if a similar reproductive period occurred off Agiabampo, at the Sonora-Sinaloa border. By combining 3 indices of mature females: size structure, abundance and fecundity at size, a single egg production index (EPI) was calculated. Monthly samples from January through December 2002 were collected during 5 continuous days around the full moon (full moon ± 2 days). Trawl net tows were used at depths from 1-9 m, 2 km north and south of the mouth of a coastal lagoon. Using the EPI, a single reproductive peak, May to August, was found, with May as the most important egg production month. On the other hand, the percentage of mature females showed a two peak reproductive period, one more intensive from May to August and the second one less intensive in November. We concluded that the best determination of the reproductive period of the brown shrimp required the use of three indices. Particularly off Agiabampo, this species has a well-defined reproductive period with just one massive spawning peak.