Significant effort has been invested in downsizing telemetry transmitters so they can be used to monitor survival and behavior in a variety of fish species and life stages. Commercially available "micro" transmitters in particular have presented researchers with the opportunity to tag very small fish (< 250 mm fork length). We conducted a release/recapture study in tandem with a laboratory study of tag effects on juvenile yearling spring and subyearling fall Chinook salmon (Oncorhynchus tshawytscha). Fish surgically implanted with both a micro-acoustic transmitter and passive integrated transponder (PIT) tags were compared with fish injected with only a PIT tag. Detections from both tag types showed that during the downstream migration, fish surgically implanted with both a micro-acoustic transmitter and PIT tag did not survive at the same rate or behave in the same manner as those injected with only a PIT tag. Differences in survival were more pronounced in subyearlings than in yearlings. This was likely due to warmer temperatures experienced by migrating subyearlings, their higher metabolic rate, and their smaller size and consequently higher tag-burden. To identify the mechanisms driving these differences, we necropsied migrating study fish recaptured at locations 225-460 km downstream from the release site. Results revealed that compared with PIT-tagged fish, micro-acoustic-tagged fish had heightened inflammatory responses within the body cavity, delayed healing of surgical incision sites, and poor body-condition. For study fish tagged along with those released to the river but held in the laboratory for observation, outcomes revealed that tag effects were similar in direction, but not as pronounced under artificial conditions.

In an attempt to develop more effective surgical implantation methods for fish, surgical incisions typical of those made for implanting micro-acoustic transmitters into the peritoneal cavity were evaluated on a weekly basis for healing progression using a suite of metrics. Additionally, four chemicals were evaluated at concentrations commonly used in aquaculture for their ability to prevent surgical site infection and thus to promote incision healing and survival. Chemical treatments included hydrogen peroxide (25, 50, and 100 mg l-1), salt (10 and 30 ppt), Argentyne (1:1, Argentyne:water), and PolyAqua (1/2 tsp 36 l-1). For all study fish, the presence of two intact sutures seven days post-surgery (generally associated with good suturing technique) was negatively correlated with survival. A generalized linear mixed effects model indicated that suture presence, increasing tagging temperature, and the presence of foreign material on sutures decreased survival by 0.56, 0.72 and 0.60 respectively. Conversely, evidence of suture tearing and increasing fork length at tagging increased survival by 0.24 and 0.17. The antiseptic treatments tested promoted neither faster healing of surgical incisions nor higher survival for fish held for 28 days compared to a reference group and two of the chemicals may be contraindicated for prophylactic use at published doses. These findings underscore the need for researchers to adopt a decidedly cautious approach to planning and interpretation of study outcomes that rely on telemetry tagging, carefully considering the study subjects, potential effects of the techniques used, and implications of the environmental conditions experienced.