Reference |
Niva, T. & P. Hyvärinen. 2001. Evacuation Rates of Coded Wire Tags Implanted in Prey of Northern Pike. North American Journal of Fisheries Management 21:692–695. |
Abstract |
In 2001–2003, all of the 400,000 juvenile brown trout Salmo trutta to be stocked into the watercourse of Lake Inari, in northernmost Finland, will be coded-wire-tagged to indicate rearing hatchery, genetic strain, site of stocking, and age of fish. One of our future objectives will be studying the relative predation by northern pike Esox lucius on stocked brown trout with respect to the different groups, as identified by coded wire tags. However, successful sampling of northern pike and the subsequent diet analysis will require answers for the following questions: Do coded wire tags injected into the snouts of juvenile brown trout accumulate in the intestine of a northern pike? If not, what is the evacuation time of the tags? Does evacuation time depend on the size of northern pike and brown trout? In experimental feeding trials, we found that coded wire tags implanted into snouts of juvenile brown trout (weight range, 28–260 g) did not accumulate in the intestine of northern pike (weight range, 303–2,942 g). The tags passed through the intestine and were evacuated in 3 d, independently of the size of northern pike and type of feeding (free versus force-fed). According to results of the present study, estimating relative predation by northern pike on coded-wire-tagged brown trout requires that stomach samples of northern pike be collected in relatively short intervals because coded wire tags are evacuated relatively quickly from the intestines of pike. On the other hand, this finding means that timing of feeding can be estimated accurately. |
Tag |
Coded Wire Tag (CWT) |
Objective |
Estimate predation rates |
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