Activity and movement patterns of the Lusitanian toadfish inferred from pressure-sensitive data-loggers in the Mira estuary (Portugal)

Activity rhythms and movement patterns of 10 adult specimens of the Lusitanian toadfish, Halobatrachus didactylus (Bloch & Schneider), were studied in the River Mira estuary (Portugal) using pressure-sensitive data-loggers and acoustic transmitters. Laboratory experiments were performed to assess the applicability of the sampling methodology to track the Lusitanian toadfish movements. Field results confirmed that the species usually displays a sedentary behaviour, although revealing a stronger disposition to perform greater longitudinal movements than it was formerly believed. Frequency of movements was influenced by the circadian cycle, tidal stage and type of tide. Lomb-Scargle periodograms revealed significant daily periodicity in all the specimens studied. Two fish displayed significant intercalary rhythms that could be related with tidal cycle. This study also indicates that this species does not exclusively adopt a sit and wait predation behaviour, but probably undertakes an active search for food.