Vemco (Canada)

Summary Acoustic telemetry is being increasingly used to study the ecology of many aquatic organisms. This widespread use has been advanced by national and international tracking programs that coordinate deployment of passive acoustic telemetry networks on a regional and continental scale to detect tagged animals. While it is well‐known that environmental conditions can affect the performance of acoustic receivers, these effects are rarely quantified despite the profound implications for tag detection and hence the ecological inferences. Here, we deployed eight receivers at different depths within the water column and at different orientations (hydrophone up or down) and 12 tags 200–800 m from the receivers for 234 days to investigate how the tag detection range of acoustic receivers varied through time and under different meteorologic and oceanographic conditions. The study showed that receiver depth and orientation, and time since deployment had the largest effect on the detection range. Thermocline gradient and depth, and wind speed were the environmental factors most affecting detection range, while wind direction, precipitation and atmospheric pressure had negligible or no effect. Comparison of results to a proposed general acoustic theory model and previous studies showed that findings from specific habitat types cannot be generalised and applied across other habitats or environments. A good understanding of the acoustic coverage and temporal variations in relation to environmental conditions are crucial to accurate interpretation of results, and ensuing management recommendations. We recommend that each study include stationary reference tags to measure changes in detection probability with time, help refine detection range, and be used to improve confidence in the reporting and interpretation of the data.

Summary Interactions between upper trophic‐level predators and their prey remain poorly understood due to their inaccessibility during foraging at sea. This uncertainty has fuelled debate on the impact of predation by species such as the grey seal (Halichoerus grypus) on fish stocks. The Vemco Mobile Transceiver (VMT) has provided us with new knowledge on interactions between pinnipeds and fish species. However, the necessity to recover the VMT for data retrieval has limited deployments to locations where confidence in instrument recovery is high, and has thus restricted both species and geographical sampling. To overcome these limitations, a Bluetooth link was integrated into the VMT and GPS satellite‐linked transmitter. The two‐unit design allows data collected by the VMT to be transmitted via Bluetooth to the satellite transmitter, which relays the interaction data to the ARGOS satellite system for retrieval. To evaluate in‐situ performance, units were deployed on two adult female grey seals on Sable Island, NS in October 2012 and recovered during the subsequent breeding season. Data archived by the VMT were compared with data uploaded via ARGOS. The deployment periods were 76–84 days. The total number of valid detections archived was 179. All detections archived by the first unit (n = 66) were transmitted via ARGOS, while all but two of the 113 archived detections from the second unit were transmitted. Detections recovered from both units were from other VMT‐tagged grey seals (n = 173) and moored V13 transmitters on Middle Bank, Eastern Scotian Shelf (n = 6). These preliminary results are proof‐of‐concept that integrated Bluetooth VMTs can be used on a broader variety of marine predators to collect data on species interactions in otherwise inaccessible environments and without the need to recover instruments.

We investigated the feasibility of measuring differential pressure of tail undulation of 6 European sea bass, Dicentrarchus labrax, averaging 0.25 kg in the laboratory and of two 1.5-kg sea bass in a salt marsh pond. Tail beat pressure was determined for sea bass swimming in a recirculating “Brett style” respirometer. Average or integrated and maximum-minimum (max-min) pressure increased as a power function with swimming speed (r2>0.95). Pressure ranged from 0 to 100 pascals (Pa) and 0 to 1000 Pa for average and for max-min pressure respectively for speeds up to 0.45 m s−1 or 2 body length s−1. Small changes in swimming speed of less than 0.05 m s−1 were readily detected as differences in tail beat pressure. We designed an ultrasonic transmitter that sampled the tail pressure and put out 10 millisecond acoustic pulses. The time between pulses was correlated to average and max-min pressure generated by the caudal peduncle.Key wordstelemetryswimming speedtail beat pressurefishsea bass