Short-term patterns of shellfish exploitation by traditional estuarine fisheries

This study assessed the number of mussel fishers at an intertidal flat at the mouth of a tropical estuary (Goiana estuary - Brazil) from January to March 2010. Two observers counted the number of fishers and fishing boats over eight tidal cycles at new moon. In addition, shell length (mm) and biomass (57.34 ± 9.7 g m−2) of fishery-independent random-samples of mussels (Anomalocardia brasiliana) were measured to estimate the resource available. Fishers’ temporal use of the intertidal flat did not significantly vary; however, average frequency of fishers on the intertidal flat decreased from 31.08 ± 17.23 in January to 21.34 ± 15.24 in March. On average, 44 fishers were counted, working ∼4 h per daytime tidal cycle. Fishing began ∼1.5 h before and ended ∼2.5 h after the lowest tide. Activity peaked from 1.5 h before until 0.5 h after the lowest tide, with the highest number of fishers on the inter-tidal flat 0.5 h before the lowest tide. Mussels were sampled independently for standing stock assessment. The most representative size of A. brasiliana was 10–12 mm, and the average density of individuals was 1600 ± 1555 m−2. The average total biomass (dry weight) was 57 ± 97 g m−2. Significant differences in shell length and biomass were observed between months. This information can help determine maximum catch per individual fisher, and the minimum size of mussels harvested. Such measures might allow mussels to reach mature adult size (>20 mm), and guarantee sustainable population dynamics and replenishment of stocks.