A new laboratory radio frequency identification (RFID) system for behavioural tracking of marine organisms

Abstract

Radio frequency identification (RFID) devices are currently used to quantify several traits of animal behaviour with potential applications for the study of marine organisms. To date, behavioural studies with marine organisms are rare because of the technical difficulty of propagating radio waves within the saltwater medium. We present a novel RFID tracking system to study the burrowing behaviour of a valuable fishery resource, the Norway lobster (Nephrops norvegicus L.). The system consists of a network of six controllers, each handling a group of seven antennas. That network was placed below a microcosm tank that recreated important features typical of Nephrops' grounds, such as the presence of multiple burrows. The animals carried a passive transponder attached to their telson, operating at 13.56 MHz. The tracking system was implemented to concurrently report the behaviour of up to three individuals, in terms of their travelled distances in a specified unit of time and their preferential positioning within the antenna network. To do so, the controllers worked in parallel to send the antenna data to a computer via a USB connection. The tracking accuracy of the system was evaluated by concurrently recording the animals' behaviour with automated video imaging. During the two experiments, each lasting approximately one week, two different groups of three animals each showed a variable burrow occupancy and a nocturnal displacement under a standard photoperiod regime (12 h light:12 h dark), measured using the RFID method. Similar results were obtained with the video imaging. Our implemented RFID system was therefore capable of efficiently tracking the tested organisms and has a good potential for use on a wide variety of other marine organisms of commercial, aquaculture, and ecological interest.

Keywords: Nephrops norvegicus; RFID; USB communication; activity rhythms; automated video imaging; burrow emergence; controller; laboratory; marine species.

Figure 1.

Details of the RFID system used to monitor the behaviour of a group of Nephrops held in a laboratory microcosm tank. (A) Details of the antenna network (the large white plates) mounted below the microcosm tank, including those placed on the tunnels (the small white plates on the grey tubes). (B) A side view of the tank showing the laptop used to acquire the RFID data from the controllers. (C) An upper view of the tank superimposed with the scheme depicting the antenna positioning (green squares numbered from 1 to 42); the antenna relationship with the controllers (from C1 to 6), covering five different areas (from 1 to 5) of the tank; and the x,y reference coordinates used to compute the animals’ displacement in centimetres. (D) A video camera field of view encompassing the whole tank surface, where the following objects are visible: the four burrows indicated by their antennas (numbers) placed inside (ⁱ = inside) or at the entrance (^e = entrance); two fully emerged and one partially sheltered animal dragging their black circular RFID transponders, indicated by the white arrows; and finally, the geometric tags used for the automated video imaging.

Figure 2.

The components of the RFID system used to individually track the behaviour of Nephrops within a laboratory microcosm tank. The different elements are A, the USB to RFID controller interface; B, the RFID controller; C, the RFID controller electronic board in detail; and D, the antennas.

Figure 3.

Organisational scheme of the relationships among the different elements composing the RFID system used to track behavioural rhythms in a group of Nephrops within a laboratory microcosm tank. The system is composed of the six controllers, each potentially connectable to seven antennas (A) and a signal storing tool (i.e., the laptop) connected via USB hubs. Although 42 antennas could have been installed, our tank specifications required us to modify this design and to reduce the number of antennas that were connected to controllers 2 and 3, see Figure 1(C).

Figure 4.

Time series of recurred distances by 6 individuals of Nephrops tracked by RFID (blue) and automated video imaging (red) in a day-night photoperiod regime (vertical grey rectangles indicate the night duration), during the first (1st) and the second (2nd) experiment.

Figure 5.

A photographic sequence of aggressive interactions between two individuals of Nephrops is presented as an example of the mechanism that generates burrow emergence rhythms of different strengths. The initial aggressive postures (A) during the approach of the animals are indicated by the forward maximum opening of the claws. This aggressive display is followed by a short contact confrontation (B). The geometric tags for the automated video imaging and the dragged black RFID transponders are also visible.

Figure 6.

Comparisons of waveform analysis outputs between locomotion activity time series (cm ± SEM) that were measured over the first (1st) and second (2nd) day-night experiment using RFID (blue) and automated video-imaging (red) tracking methods for three Nephrops held together in a laboratory microcosm tank. The MESOR is the horizontal line. The arrows indicate the onset and offset of peaks (i.e., values above the MESOR) and are used for a comparison between the two tracking methods.

Figure 7.

Inter-individual differences in the occupied areas of a group of three Nephrops, detected using RFID tracking during the first (1st) and second (2nd) day-night experiment. The blue circles are proportional to the percentage of occupation, computed from the cumulative detections in each antenna field over the duration of the experiment. The red circles indicate the entrances of the four tunnels, with their location superimposed onto a picture of the tank area for which the length and width coordinates have been also reported as a system of x,y coordinates, see Figure 1(C).