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Comparison of Three Nonlinear Models to Describe Long‐Term Tag Shedding by Lake Trout
Author(s) -
Fabrizio Mary C.,
Swanson Bruce L.,
Schram Stephen T.,
Hoff Michael H.
Publication year - 1996
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1577/1548-8659(1996)125<0261:cotnmt>2.3.co;2
Subject(s) - trout , salvelinus , shoal , fish <actinopterygii> , fishery , brown trout , environmental science , term (time) , biology , ecology , physics , geology , oceanography , quantum mechanics
We estimated long‐term tag‐shedding rates for lake trout Salvelinus namaycush using two existing models and a model we developed to account for the observed permanence of some tags. Because tag design changed over the course of the study, we examined tag‐shedding rates for three types of numbered anchor tags (Floy tags FD‐67, FD‐67C, and FD‐68BC) and an unprinted anchor tag (FD‐67F). Lake trout from the Gull Island Shoal region, Lake Superior, were double‐tagged, and subsequent recaptures were monitored in annual surveys conducted from 1974 to 1992. We modeled tag‐shedding rates, using time at liberty and probabilities of tag shedding estimated from fish released in 1974 and 1978–1983 and later recaptured. Long‐term shedding of numbered anchor tags in lake trout was best described by a nonlinear model with two parameters: an instantaneous tag‐shedding rate and a constant representing the proportion of tags that were never shed. Although our estimates of annual shedding rates varied with tag type (0.300 for FD‐67, 0.441 for FD‐67C, and 0.656 for FD‐68BC), differences were not significant. About 36% of tags remained permanently affixed to the fish. Of the numbered tags that were shed (about 64%), two mechanisms contributed to tag loss: disintegration and dislodgment. Tags from about 11% of recaptured fish had disintegrated, but most tags were dislodged. Unprinted tags were shed at a significant but low rate immediately after release, but the long‐term, annual shedding rate of these tags was only 0.013. Compared with unprinted tags, numbered tags dislodged at higher annual rates; we hypothesized that this was due to the greater frictional drag associated with the larger cross‐sectional area of numbered tags.