The Effect of Short‐Duration Seawater Exposure and Acoustic Tag Implantation on the Swimming Performance and Physiology of Presmolt Juvenile Coho Salmon

Abstract

AbstractTo assess the potential impact of “tag effect” on seaward‐migrating Coho Salmon Oncorhynchus kisutch, presmolt juveniles were surgically implanted with acoustic transmitters followed by exposure to freshwater (FW, 0‰ salinity) or seawater (SW; 30‰ salinity) for 24 h and then subjected to repeated critical swimming speed (Ucrit) trials. Three different experimental tag‐treatment groups were established: control (no surgery), sham (surgery but no tag), and tagged (surgically implanted tag), with a range of 9–12 fish in each group. Tagged fish were implanted with Vemco V6 dummy acoustic transmitters (DAT: 17.0 mm long × 6 mm diameter, 1.0 g in air). After completion of two Ucrit trials, separated by a recovery period, all fish were euthanized and sampled to determine hematocrit (Hct) and plasma osmolality. In the FW exposure, the mean Ucrit of the control treatment was significantly higher than that of the tagged treatment (P = 0.04). No significant differences in swimming performance were observed among the SW treatment groups, and no significant differences were observed between Ucrit trials (Ucrit1 and Ucrit2) for any of the experimental treatments groups. Seawater exposure did, however, result in slightly reduced, but not statistically different, swimming speeds and concomitantly higher plasma osmolalities (P < 0.001) compared with FW exposure. Predictions made with data from this study suggest that sample sizes (per tag treatment) of n = 25 are sufficient to detect a 15–20% difference in Ucrit sample means with 80% power. Collectively, these data do not provide substantial statistical evidence that the swimming performance of juvenile Coho Salmon tagged with surgically implanted acoustic transmitters is significantly reduced compared with untagged fish.