Tags

Examples of the various tags in use

Acoustic tags are now small enough to be implanted into animals of about 10 cm long or greater and have usable lifespans of greater than 6 months (lifespan depends on the programming and the scientific objectives). For larger tags, battery life spans of 20 years are possible. Characteristics such as size, battery life, transmission schedule, and signal strength are traded off against one another depending on the goals of the study. For Pacific salmon smolts, V9 tags (9 mm diameter by 22 mm long) or V7 tags (7 mm diameter by 17.5 mm long) are used. These small tags have battery lives of 4-12 months.

Battery life in acoustic tags depends on the transmission schedule and signal strength. Although a longer battery life is desirable, it is also important to ensure that the tags are emitting signals frequently enough to maximise the chance of detection by receivers in the ocean. As part of the early project development to lay the groundwork for POST, substantial effort went into developing an optimal balance between tag emission characteristics, array geometry, and technical constraints such as battery life. The 2004-2005 demonstration phase showed that this design could achieve a detection efficiency of 93% or greater.