The tags broadcast as long as the battery lasts. They have been recorded in Great Blue Heron, for example. A smolt is "dead" when it does not pass the next downstream line of receivers. In some cases, they can get by one line and are recorded at the next. Plus, a smolt may decide to remain in FW for another year. Battery dies, it survives and smolts, but would likely be considered a mort from the year before.

As with all stuff biological, you need years of data, consistently collected, to detect trends. This "one year of data and we have what we need" does save money but is stupid.