Field Trials of Marking Stream Salmonids by Dye Injection and Coded-Wire-Tagging

Abstract

In the summers of 1993 and 1994, we conducted trials in natural streams to assess the performance of dye marks and full-length coded wire tags (CWTs) when used simultaneously. Brook trout Salvelinus fontinalis and juvenile Atlantic salmon Salmo salar (fork length ≥55 mm) were marked with jet injection of Alcian Blue dye (in the base of the pectoral, pelvic, or caudal fins) and CWT (snout implant). All Alcian Blue marks remained clearly visible for at least 4 weeks. After 8 weeks, 3.1 % of brook trout and 11.4% of Atlantic salmon had lost at least one mark. Although loss rates did not differ significantly among marking locations, 86% of mark losses were from the caudal fin. Marking in pelvic or pectoral fin locations induced high mortality in smaller fish. Dye retention was low for individuals recaptured 10–14 months after injection, presumably because interannual growth caused dilution of the mark. Loss rates of CWT in summer were 2.5% for brook trout and 8.4% for Atlantic salmon; for either species, loss rates did not differ significantly among size-classes. Marked fish did not differ from unmarked fish in growth or condition in summer.