External attachment was the most common telemetry tag attachment method for fish studied in the first two decades (1956–1975) of application, but was overtaken in popularity in the 1980s by surgical implantation in the body cavity, largely due to tag miniaturization and extended battery life. The main methods for attaching electronic tags to fish are surgical implantation in the body cavity, gastric insertion, and external attachment. In general, the combined effect of capture, handling and tagging may change an animal’s behavior, and lead to flawed results in telemetry studies.Įlectronic tagging (referred to as telemetry and bio-logging) of free-ranging animals is widely used to study fish spatial ecology, survival, and responses to the environment.
Results from a study of fish activity have convinced me of the need for careful examination of this problem”. More than four decades ago, Bruce Shepherd wrote: “Although many researchers have looked in a cursory fashion at transmitter attachment and its effect on fish behavior, none have done so in detail. Before embarking on a field study employing external tagging with electronic tags, we recommend the use of appropriate pilot studies, controlled where possible, to quantify potential impacts of tagging. For PSATs, especially those that are large relative to fish size, there are particular problems with a high proportion of premature tag losses, reduced swimming capacity, and likely increased predation, but there remains a paucity of tag effect studies related to the use of PSATs. There is a general need for more research on the effects of external tagging of fish with electronic tags, but particularly there are few studies on predation risk, social interactions, and studies distinguishing capture and handling effects from tagging effects. Most of the studies reviewed evaluate tag retention, survival, and tissue reactions. Reduced growth and survival have also been recorded, but direct mortality caused by external tagging seems rare. The most commonly reported problems with external tags are tissue damage, premature tag loss, and decreased swimming capacity, but the effects are highly context dependent and species specific. External attachment holds certain benefits compared to other tagging methods, for example, speed of application, and it may be the only option for fishes with a body shape unsuitable for surgical implantation, or when using tags with sensors recording the external environment. We identified 89 publications, reporting effects of external tagging for 80 different fish species, which constitute the main basis for this review. Scientific evaluations of the tagging method are rather scarce for most species. Recently, the number of telemetry studies using external tagging has increased, especially with the development of archival tags (data storage tags, DSTs), pop-up satellite archival tags (PSATs) and other environment-sensing tags. In the early years of fish telemetry research, it was the most commonly used attachment method, but later internal implants became preferred.
External tagging of fish with electronic tags has been used for decades for a wide range of marine and freshwater species.
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