Long‐term retention of coded wire tags in juvenile Arctic charr Salvelinus alpinus

Abstract

A hatchery experiment was organised to find out if the high loss rate of coded wire tags, noticed in connection with an Arctic charr Salvelinus alpinus (L.) restocking programme, was size-dependent and also to test head moulds for future taggings. Six moulds made by Northwest Marine Technology Inc. and five moulds made at the Finnish Game and Fisheries Research Institute were used. A total of 100 charr were tagged with standardlength coded wire tags using each mould. One-summer old charr at tagging were held for 534 days and twosummer old charr for 320 days. The tag loss rate varied between 0% and 54% and was negatively related to the size of the charr at tagging. The high loss rate was connected with the poor alignment of some moulds, such that a large proportion of the tags were located in the nasal cavity instead of the nasal cartilage. Testing of the moulds and careful grading of the fish for tagging is emphasised, especially if Arctic charr smaller than 20 g in weight are to be tagged. K E Y W O R D S :Arctic charr, coded wire tag, hatchery experiment, head mould, tag retention.

Evaluation of Coded Wire Tag Loss in Brook Trout Tagged Using Automated Methods

“…Tag loss reported for Rainbow Trout (1.5 ± 1.2% [mean ± SE]; Hale and Gray ) appears lower than that in Brook Trout but again is probably similar given that the Rainbow Trout, although manually tagged, were considerably larger (mean lengths = 180–244 mm) than the Brook Trout in our study. Tag loss also appeared to be considerably lower in Brook Trout than in the congener, Arctic Char (0.0–54.0% for 97–238‐mm fish during manual tagging; Kolari and Hirvonen ), although poor alignment of smaller fish with the head molds used for tagging was thought to be the cause of higher tag loss. The most straightforward comparison is between Brook Trout and Lake Trout (Kornis et al.…”

“…() noted that tag loss in Lake Trout ranged from 0.0% to 14.0% over 197 automated tag lots and from 0.0% to 32% over 1,080 manual tag lots. Second, fish size at tagging also likely plays a role in tag loss, with several studies noting higher tag loss rates from smaller fish (Blankenship ; Kolari and Hirvonen ). Given those factors, tag loss in Brook Trout (1.3–2.6% across three year‐classes) appears lower than that observed in Chinook Salmon and Coho Salmon (1.1–5.3% across eight test groups; Blankenship ) but is probably more similar among these species given that the Brook Trout were larger (mean lengths of 79–91 mm compared to 54–62 mm [from length–weight conversion of weight values in Blankenship ]) and were tagged using automated versus manual methods.…”

“…We hypothesized that tag loss would take 150 d or more to stabilize in Brook Trout, similar to the tag loss stabilization periods observed for other Salvelinus spp. (Kolari and Hirvonen ; Kornis et al. ).…”

“…). Tag loss has been observed as high as 54% in some Arctic Char Salvelinus alpinus tag lots due to poor tag placement in small fish (Kolari and Hirvonen ).…”

“…By contrast, tag loss stabilized after about 150 d for Lake Trout (Kornis et al. ) and after 175–320 d for Arctic Char (Kolari and Hirvonen ). Stabilization time appears to be positively correlated with tag loss, at least in Arctic Char (Kolari and Hirvonen ).…”