The results from this study were obtained using an innovative technological approach, the AccelTag, developed and previously tested in controlled laboratory conditions . In the present work, it was used for the first time to obtain in situ detailed foraging behaviour data of an aquatic animal. AccelTag proved to be a powerful tool to assess and monitor the fine-scale behaviour of a resident estuarine fish. In terms of ecological data obtained with AccelTag, the main findings are concordant with results obtained with other works that used distinct methodological approaches to study the Lusitanian toadfish foraging behaviour [21,22,23,24]. When comparing to other available tools (see  for further discussion) such as data storage tags with accelerometer sensors [6, 7], and even more recent acoustic transmitters equipped with three-axis accelerometer sensors [8,9,10,11, 25, 26], the AccelTag has the advantage of being able to process the fine-scale acceleration information autonomously and acoustically transmit the correspondent behaviour. Several authors have identified advantages of data processing and compression, e.g., increased tag autonomy, reduced storage requirements and reduced data analysis time [11, 27]. Moreover, the work previously developed , combined with the present study corresponds to the anticipated studies and technological enhancements proposed , namely the tagging of captive specimens to calibrate the software accordingly to distinct behaviours, and then implement in situ behaviour studies.
With regard to the foraging ecology of the Lusitanian toadfish, tides and circadian cycle, together with the time of year, seem to play an essential role in the behaviour of this species. Notwithstanding being capable of swimming over relatively large distances [22, 23], specimens typically do not perform significant displacements and remain most of the time inactive (97.5% of the time in the present study), buried in the sediment or concealed in rocky crevices. In fact, the majority of the specimens remained within the study area for almost the entire study period, some of them returning to the capture site after being tagged and released. However, this sedentary behaviour was amplified by the time of the year when the study occurred. Moreover, this species is more active during the spawning season, which occurs in late spring and early summer [17, 18], whereas this study was performed in late summer and mid-autumn when the specimens tend to reduce global activity and decrease the number of long displacements .
Tidal stage influenced toadfish behaviour and activity in larger cycles of time. During spring tides of higher amplitudes, the activity increased and the number of potential attacks diminished. This pattern may be related to strong water currents associated with this period that force toadfish to actively avoid being dragged away and, consequently, reduce feeding activity. After this period of reduced feeding attempts, during neap tides, attacks considerably increase and activity level decreases. Variations on tidal stages also explain the marked pattern of burrowing and re-burrowing movements. These are more frequent during spring tides, when toadfish need to refuge (i.e., remain buried) to avoid being displaced by strong water currents, and decrease during neap tides.
On the other hand, the tidal cycle only influenced toadfish behaviour and activity in interaction with the time of day. Indeed, the number of attacks and activity were influenced synergistically by those two factors. Toadfish were more active during night-time, confirming previous findings in the same estuary [22, 23]. The nocturnal period is the preferred for engaging feeding activities as their prey are also more active. Subsequently, the number of attacks also increased during the night period. Additionally, high tide phases considerably improve visibility in the lower Mira Estuary due to the input of more transparent water from the ocean. As previously observed in laboratory experiments , toadfish is a visual predator attacking its prey mostly based on movement. Therefore, the combination of high tide with night-time results in a favourable period for toadfish to feed. As highlighted by  these higher activity periods displayed by the Lusitanian toadfish are not independent of the activity of its prey, most of them displaying higher activity or vulnerability to predation during the night and at high tide periods.
The influence of the time of year was evident in the differences between the two groups of toadfish tagged. The first group of toadfish was tagged and tested in late summer, close to the end of the spawning season. Moreover, the year of 2010 presented a relatively rainy and cold spring, which delayed the spawning season of this species, which is highly influenced by water temperature . Therefore, global activity is relatively high at the beginning of the study, gradually reducing in the following 12 days. During this period, the tagged toadfish also performed more attacks, as it is expected at the end of the reproductive period . Concerning the second group of toadfish, it was monitored in mid-autumn, far from the spawning season and closer to the winter. This period corresponds to the time of year when this species is less active . This discrepancy between the times of the year in which the two groups were monitored may explain detected differences in burrowing and re-burrowing movements and activity levels, with toadfish tracked in summer performing more of these behaviours and toadfish tracked in autumn being globally more active. However, the number of attacks did not significantly differ between seasons, which may suggest that the higher activity observed with the toadfish tracked in autumn may be related to the search for shelters instead of food. Therefore, both groups were influenced by tide and time of day, but differences between groups are probably related to the species circannual lifecycle.