Tagging causes tissue damage, decreased swimming capacity, reduced growth, increased predation, and an increased chance of death.
"The most commonly reported problems with external tags are tissue damage, premature tag loss, and decreased swimming capacity."
"Reduced growth and survival have also been recorded."
"For PSATs (pop-up satellite archival tags), especially those that are large relative to fish size, there are particular problems with a high proportion of premature tag losses, reduced swimming capacity, and likely increased predation."
"Reduced swimming performance is one of the expected effects of attaching external tags to fish because of the additional drag exerted by the tag as the fish moves through the water. External tags will change the streamlined body shape that many fish species possess, disturb balance and, at worst, cause loss of equilibrium if the tag is too heavy compared to the mass of the fish. Predatory species that rely on speed to catch prey may be less successful and suffer reduced growth. For prey species dependent on escaping predators, the additional drag and weight of a tag may skew the balance between life and death."
"For migrating species, changes in swimming performance may delay or reduce migration success."
"In an early study, Shepherd reported a swim trial where the oxygen consumption rate of externally tagged wild cutthroat trout was compared with control fish. The study demonstrated a higher oxygen demand of tagged fish. A similar approach with small numbers of tagged and untagged cod showed a higher mass-specific oxygen consumption rate of tagged fish during swimming, indicating that there is a measurable drag effect from the tag, as predicted by Arnold and Holford. In a study of the effect of external tagging on juvenile rainbow trout, Lewis and Muntz used tail beat frequency, opercular beat rate, and drag measurements as indicators of swimming performance. All three indicators were elevated in tagged fish compared to controls, and a pannier-saddle-mounted tag, generating more drag than a single-side mount, caused a greater impact. Tests with a dorsal saddle-type tag on the same species showed that time to exhaustion was shorter for externally tagged fish than for surgically implanted and control fish. The same test with white perch showed large individual variation, but no difference was found between treatments."
"In general, these studies document a measurable effect on oxygen demand and swimming performance from fishes carrying an external electronic tag. This effect is most pronounced in relatively small fish, or when large buoyant tags have been applied."
"External tags may affect feeding and thus growth, because movement can be impaired by the presence of the tag. Furthermore, capture, handling, holding, and tagging may compromise the health of a fish, affecting the motivation and physical capability for feeding. External tags also involve additional mass and drag, which may result in increased energy expenditure and reduced growth, even if the fish is feeding normally. Thus, growth integrates a range of effects into one measurable parameter, because reduced performance will likely result in a reduced growth. Growth rate can, therefore, be a good indicator of long-term effects."
"Tank-reared barbel with side-mounted external dummy Tags (2% of body mass) lost an average of 10% of their body mass in the 60 days post tagging."
"Studies show negative effects on growth or body condition in Atlantic salmon juveniles, yellow perch, bluegill."
"A tagged fish might migrate a shorter distance and at a slower speed than an untagged fish."
"External tags are often attached with stainless steel wires or nylon filaments through the muscle at the dorsal fin, with the tag resting at the skin below the fin."
"Combined effects of capture and handling may be even more important for the welfare of the fish and the outcome of the study than tagging itself."