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.
Highlights
The Sacramento–San Joaquin River Delta produces the majority of Chinook Salmon (Oncorhynchus tshawytscha) caught in California’s ocean fisheries (Kano 2006)
Juvenile salmon survival in the Delta has been estimated for several years using acoustic telemetry, and, like most other industries, the technology has improved over time
Fish were netted from the raceway and individually weighed; those above 7.0 g were transferred into a 300-gal (1,135-L) tank held in the bed of a pick-up truck and transported to the Tracy Fish Collection Facility (TFCF; U.S Bureau of Reclamation, Tracy, CA) with supplemental oxygen
Summary
The Sacramento–San Joaquin River Delta produces the majority of Chinook Salmon (Oncorhynchus tshawytscha) caught in California’s ocean fisheries (Kano 2006). Any inferences made to the population of interest may be invalid if significant tagging effects exist, such as reduced swimming performance, growth rate, or foraging capability (Bridger and Booth 2003; Brown et al 2011; Cooke et al 2011; Liedtke and Wargo–Rub 2012; Cooke et al 2013) These problems have been remedied in other studies, in part by limiting the tag burden (i.e., the ratio of tag weight in air-to-body weight; Brown et al 2010; Ammann et al 2013), since small tags and low burden rates are less likely to cause tag effects (Barnard and Brandes, unpublished data, see “Notes”; Brown et al 2010)
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