Background

Artisan fishermen along the southern Sinaloa coast catch alternative species, for example the Grapsus grapsus rock crab without biological and fishing controls, when their catches are reduced or when the season for catching certain fish has ended.

Goals

We analyzed the size structure and biometric relationships of G. grapsus on Lobos, Venados, and Pájaros Islands of Mazatlán Bay, Sinaloa, Mexico.

Methods

The cephalothorax width (CW) and weight (W) were analyzed during a one-year period (March 2012-February 2013).

Results

926 organisms were collected (519 males y 407 females). Pájaros Island had the greater percentage (37.4%) of collected organisms, followed by Lobos (34.2%), and Venados (28.4%) Islands. The greatest values were CW=74.5 mm recorded at Pájaros Island and W = 138.2 g at Venados Island and the lowest values were CW=13.9 mm at Pájaros Island and BW =1.1 g at Lobos Island. Means of CW and W were 41.4 mm and 31.5 g, respectively. The means of CW and W were statistically different between the islands (CL, p = 0.009; W, p < 0.015).

Conclusions

High determination coefficients between the variables were obtained, indicating isometric growth. Specimens of G. grapsus increase their size quickly and their weight very slowly.