The recent introduction of low-cost, moored data-logging acoustic receivers has provided opportunities for tracking marine organisms over small (hundreds of metres) and large scales (hundreds of kilometres). Acoustic receivers have been deployed in many different environments to examine specific hypotheses regarding the movement of aquatic species. This technology provides many advantages for studying aquatic animal movement patterns, but also has limitations and provides unique difficulties for users. Study design, applications, advantages and limitations are discussed with examples from past and current studies. Data management and analysis techniques are in their infancy and few standardised techniques exist. Complications with data management and potential data analysis techniques are discussed. Examples from the literature are utilised wherever possible to provide useful references.

Automated acoustic tracking of aquatic animals: scales, design and deployment of listening station arrays

Considerable technical developments over the past half century have enabled widespread application of electronic tags to the study of animals in the wild, including in freshwater environments. We review the constraints associated with freshwater telemetry and biologging and the technical developments relevant to their use. Technical constraints for tracking animals are often influenced by the characteristics of the animals being studied and the environment they inhabit. Collectively, they influence which and how technologies can be used and their relative effectiveness. Although radio telemetry has historically been the most commonly used technology in freshwater, passive integrated transponder (PIT) technology, acoustic telemetry and biologgers are becoming more popular. Most telemetry studies have focused on fish, although an increasing number have focused on other taxa, such as turtles, crustaceans and molluscs. Key technical developments for freshwater systems include: miniaturization of tags for tracking small-size life stages and species, fixed stations and coded tags for tracking large samples of animals over long distances and large temporal scales, inexpensive PIT systems that enable mass tagging to yield population- and community-level relevant sample sizes, incorporation of sensors into electronic tags, validation of tag attachment procedures with a focus on maintaining animal welfare, incorporation of different techniques (for example, genetics, stable isotopes) and peripheral technologies (for example, geographic information systems, hydroacoustics), development of novel analytical techniques, and extensive international collaboration. Innovations are still needed in tag miniaturization, data analysis and visualization, and in tracking animals over larger spatial scales (for example, pelagic areas of lakes) and in challenging environments (for example, large dynamic floodplain systems, under ice). There seems to be a particular need for adapting various global positioning system and satellite tagging approaches to freshwater. Electronic tagging provides a mechanism to collect detailed information from imperilled animals and species that have no direct economic value. Current and future advances will continue to improve our knowledge of the natural history of aquatic animals and ecological processes in freshwater ecosystems while facilitating evidence-based resource management and conservation.

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Tracking animals in freshwater with electronic tags: past, present and future

Remote sensing technologies have been used to study the behaviour and movements of fish in the sea for about 30 years. The first relatively simple devices have given rise to a suite of sophisticated tools that have spawned a whole new field of fisheries science. The oldest method, acoustic telemetry, has now advanced to the level at which we can study detailed behaviour in the field in relation to the immediate environment, and monitor physiological variables, as well as document larger-scale movement patterns. Archival tags, available for the last 7–8 years, provide a powerful tool to obtain detailed information on a range of variables for large number of individual fish over long periods of time. Their primary limitation is that they must be recovered to obtain the data. The most recent development, the pop-up satellite tag, requires no recovery and can thus be used on any fish of sufficient size. Being fully independent of the fisheries, this type of tag is ideal for studying large, highly migratory fish and dramatically expands the scope of questions that can be addressed. The pace of technical development will undoubtedly continue to accelerate over the next few decades, producing new tools that can be expected to solve many currently unanswered questions in fisheries biology. Solutions to these questions should help to achieve improved management of the seas and their living resources.

Electronic Tags in Marine Fisheries Research: A 30-Year Perspective

Although the whale shark Rhincodon typus is the largest extant fish, it was not described until 1828 and by 1986 there were only 320 records of this species. Since then, growth in tourism and marine recreation globally has lead to a significant increase in the number of sightings and several areas with annual occurrences have been identified, spurring a surge of research on the species. Simultaneously, there was a great expansion in targeted R. typus fisheries to supply the Asian restaurant trade, as well as a largely un-quantified by-catch of the species in purse-seine tuna fisheries. Currently R. typus is listed by the IUCN as vulnerable, due mainly to the effects of targeted fishing in two areas. Photo-identification has shown that R. typus form seasonal size and sex segregated feeding aggregations and that a large proportion of fish in these aggregations are philopatric in the broadest sense, tending to return to, or remain near, a particular site. Somewhat conversely, satellite tracking studies have shown that fish from these aggregations can migrate at ocean-basin scales and genetic studies have, to date, found little graphic differentiation globally. Conservation approaches are now informed by observational and environmental studies that have provided insight into the feeding habits of the species and its preferred habitats. Notwithstanding these advances, there remain notable gaps in the knowledge of this species particularly with respect to the life history of neonates and adults who are not found in the feeding aggregations.

http://elasmollet.org/PublicationsOthers/rowat_brooks_2012_whale_shark_review.pdf

A review of the biology, fisheries and conservation of the whale shark Rhincodon typus.

The effects of intraperitoneally implanted dummy acoustic transmitters on juvenile Atlantic salmon Salmo salar of comparable size to wild presmolts and smolts were examined in two laboratory experiments. In the first experiment, different-sized tags (24, 28, and 32 mm × 8-mm diameter) that mimicked acoustic transmitters suitable for long-term studies were assessed. There was 60% mortality (3 of 5 fish) with the 32-mm implant early in the 316-d study and 20% mortality (1 of 5 fish) with the 28-mm implant. All fish surviving with 28- and 32-mm implants eventually expelled their tags, compared with only 20% of fish (1 of 5) with the 24-mm implant. Tag expulsion was not a cause of death. After implantation, tags were first encapsulated in a thick membrane and then expelled between 142 and 217 d after surgery, exiting at a site where pressure of the tag on the abdominal wall was greatest. Growth of tagged fish was initially delayed and lagged that of control and sham-tagged fish, but survivors from th...

Effects of Implanted Dummy Acoustic Transmitters on Juvenile Atlantic Salmon

Miniature pingers and automated receivers were developed and tested over three years to track Atlantic salmon smolts of different size and origin as they migrated from fresh water and at sea. Pingers (8 mm diameter × 38 mm) with delayed activation were first tested and surgically implanted in large hatchery-reared smolts (31 cm). After improvements, these pingers were implanted in smaller hatchery smolts (23 cm) in a second study. They were detected by automated receivers at fixed sites and tracked at sea as far as 49 km. Range of detection was at least 400 m, and duration of improved pingers exceeded 75 d. Pingers were then reduced in size (8 mm × 26 mm) by using a custom integrated circuit, and they were implanted and tested in wild smolts (18 cm) in a third study. They were tracked over the same period and distances as the previous year. Power output was maintained and signal strength and range of detection were as good as for the larger pingers, and pinger duration was up to 86 d. In all tests, the frequency of transmitters was crystal controlled for decoding by the narrow-band automated receivers moored underwater at fixed sites. A laboratory study to examine the long-term effects of surgically implanting dummy pingers of different sizes (8 mm × 24, 28, and 32 mm) in juvenile salmon (15 cm) indicated that pinger shape needed modification to increase retention time past 5–6 mo and that pinger size should be reduced further to eliminate mortality. These studies have led to the development of miniature coded transmitters and small single-channel receivers which will make it possible to detect and track large numbers of small, wild salmon smolts over long distances and for several months at sea.

J. M. Anderson

Papers

Development of miniature pingers for tracking Atlantic salmon smolts at sea