Survival, tag retention, growth, and wound healing of juvenile chinook salmon (Oncorhynchus tshawytscha) surgically implanted with a dummy acoustic tag

Abstract

Tag effect studies are paramount in interpreting the results of survival studies. The objective of this study was to analyze the influence of tag implantation and tag burden on the survival, tag retention, growth, and wound healing of juvenile Chinook Salmon 7.8 ± 0.9 g initial weight. Fish were obtained from the Merced River Hatchery, held for 7 d, and then surgically implanted with Juvenile Salmon Acoustic Telemetry System (JSATS) SS300 dummy tags (0.3 g in air). Tag burden ranged from 2.9-4.8% (3.86 ± 0.43%, mean ± standard deviation). Weight and fork length were taken immediately before tag implantation. All fish (i.e., control and dummy-tagged) were also implanted with a visible implant alpha tag next to the dorsal insertion. Control and dummy-tagged fish were held in a single tank for 30 d. Any fish that died during the 30-d period were noted. At the end of the holding period, all fish were euthanized, weighed, measured, and necropsied. All dummy-tagged fish retained their dummy tag, and survival rates between the two groups were similar. Wound healing was also similar across the range of tag burdens analyzed. Specific growth rates, however, differed significantly between the two groups, with control fish growing at a rate of 1.08 ± 0.38% d-1 compared to 0.55 ± 0.48 % d-1 in dummy-tagged fish (P < 0.001). Tag burdens and specific growth rates for dummy-tagged fish (P = 0.961) did not correlate, nor did initial weight and specific growth rate for control (P = 0.363) or dummy-tagged (P = 0.983) fish. The cause of the decreased growth rate in dummy-tagged fish remains unknown. Determining the cause of decreased growth in tagged juvenile Chinook Salmon, and how that decreased growth may influence survival in the wild, should be investigated further.