Objective.

The sex ratio, proportion of ovigerous females, length at sexual maturity and fecundity of Grapsus grapsus crabs in the Lobos, Venados and Pajaros islands (southeastern Gulf of California) were analyzed.

Materials and methods.

Sampling was conducted monthly between March 2011 and February 2012, during the night at low tide. Thirty crabs were collected in a quadrant (25 m2) at each sampling site on each island. cw (mm) and w (g) were determined. The sex ratio and size at sexual maturity (cw50%) were estimated, and for ovigerous females, embryonic stages and fecundity (gravimetric method) were determined.

Results.

The sex ratio (M:F) was 1:1.3. The average size at sexual maturity (cw50%) was 34.9 mm. The majority of females were ovigerous (71.3%), and 48% of the embryos of ovigerous females were at the red-orange phase. Egg diameter ranged from 1.1 to 5 µm, with an average of 2.05 µm. The mean fecundity was 24339.3 eggs. The maximum and minimum weight of ovigerous females was 69.9 and 15.2 g.

Conclusions.

The studied characteristics of sex ratio, proportion of ovigerous females, length at sexual maturity and fecundity of G. grapsus, indicate the effective administration and management of this resource in this area.

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