Long-term PIT tag retention rates in Atlantic salmon (Salmo salar)

Abstract

Background: Passive integrated transponder (PIT) tags are widely used in studies of various aspects of fish survival, movement and behaviour. Quality of such studies depends on the fish retaining the tags over the study period and that the tagging procedure or the tag does not influence behaviour or survival. Here we document PIT tag retention rates in hatchery-reared Atlantic salmon over a 533-day period from the late juvenile freshwater stage (pre-smolts) to young adults after 1 year in seawater. Fish were marked with 12-mm PIT tags, injected into their body cavity, as age 1+ pre-smolt and scanned for presence of PIT tags five times during the study.Results: Tag retention for the entire period was 91% and varied between periods (96.09-99.89%). For individual time steps, daily retention rate was lowest in the first period following tagging (days 0-49). After this period retention rate increased substantially, before again dropping close to initial levels at the two last periods (days 173-533). Length of fish was only significantly related to retention during the first period. No difference in retention rates was found between males and females. A subset of fish without detected tags was X-rayed to verify that lack of PIT detection was due to tag loss. Conclusion:The retention rates observed in this study clearly show that tag loss needs to be accounted for when analysing PIT tag data on Atlantic salmon. Further, the temporal changes in retention rate clearly challenge previous assertions that tag loss is something that primarily occurs shortly after tagging or during spawning.

Testing the applicability of tagging the Great crested newt (Triturus cristatus) using passive integrated transponders

“…That experiment started with 2 986 fish, and during the entire period PIT tags were not detected in 191 fish. Observed tag retention rates of 12.5 mm PIT tags implanted in the body cavity of Atlantic salmon over a 533 day period was 91% [72]. Low PIT tag retention rates of larger fish in studies of other Salmonidae species have been ascribed to tag loss during spawning [51, 73, 74].…”

“…In addition to tag expulsion with eggs, there are several ways tags can exit the fish: through the incision, through the body wall, and through the intestine [71]. Visual inspection of fish without tags from the fourth and fifth scanning did not reveal any obvious signs of tags having exited through the body wall [72]. In a study on birds, the overall PIT tag retention was 77.2% (N = 102); 12% (N = 6) of male and 29% (N = 24) of female tags were lost during the study period.…”

Telemetry and genetics reveal asymmetric dispersal of a lake‐feeding salmonid between inflow and outflow spawning streams at a microgeographic scale

“…Consequently, we cannot unequivocally confirm that the putative straying behavior detected during this study resulted in effective dispersal. On the other hand, it is possible for female salmonids to shed PIT tags during spawning (Bateman, Gresswell, & Berger, 2009;Foldvik & Kvingedal, 2018;Taylor et al, 2011). Indeed, such tag loss by females may account for the male bias observed among putative strayers.…”

Long‐term retention of dummy acoustic transmitters in adult brown trout

“…(Jepsen, 2003; Jepsen et al ., 1999). Intra‐peritoneal implanted tags can, however, be lost with potential shedding routes through the incision scar, transdermally, via the intestine or during spawning activities (Foldvik & Kvingedal, 2018; Moore et al ., 1990). Jepsen et al .…”

“…Some previous studies have documented full retention of implanted tags in freshwater species such as pike (Esox Lucius L.) (Jepsen & Aarestrup, 1999) and pike-perch (Stizostedion lucioperca L.) (Jepsen, 2003;. Intraperitoneal implanted tags can, however, be lost with potential shedding routes through the incision scar, transdermally, via the intestine or during spawning activities (Foldvik & Kvingedal, 2018;Moore et al, 1990). Jepsen et al (2002) suggested that tag losses could be quite variable between species or age classes and often took place shortly after tagging in juvenile fish and during spawning in adults.…”