A comparison of single-suture and double-suture incision closures in seaward-migrating juvenile Chinook salmon implanted with acoustic transmitters: implications for research in river basins containing hydropower structures

Reductions in the size of acoustic transmitters implanted in migrating juvenile salmonids have resulted in the ability to make smaller incisions that may warrant using only a single suture for closure. However, it is not known if one suture will sufficiently hold the incision closed, particularly when outward pressure is placed on the surgical site, such as when migrating fish experience pressure changes associated with passage at hydroelectric dams. The objective of this research was to evaluate the effectiveness of single-suture incision closures on juvenile Chinook salmon (Oncorhynchus tshawytscha). Juvenile Chinook salmon were surgically implanted with a 2012 Juvenile Salmon Acoustic Telemetry System (JSATS) transmitter (0.30 g) and a passive integrated transponder tag (0.10 g), and incisions were closed with either one suture or two sutures. Mortality and tag retention were monitored, and tagged fish were examined after 7 and 14 d to evaluate tissue responses. In a separate experiment, surgically implanted fish were exposed to simulated turbine passage and then examined for expulsion of transmitters, expulsion of viscera through the incision and mortal injury. With incisions closed using a single suture, there was no mortality or tag loss and similar or reduced tissue reaction compared to incisions closed with two sutures. Furthermore, surgery time was significantly reduced when a single suture was used, which led to less handling time and time under anesthesia and consequently, stress. No tags were expelled during pressure scenarios. Expulsion of viscera occurred in two non–mortally injured fish (5%) with single sutures that were exposed to very high pressure changes, but no viscera expulsion was present in fish exposed to pressure scenarios, likely representative of hydroturbine passage at many Columbia River dams (for example, <2.7 ratio of pressure change, acclimation pressure of 146.2 absolute kPa and lowest exposure pressure of about 53.3 absolute kPa). We recommend the use of a single suture for surgical implantation of transmitters with incisions that are approximately 5.5 mm long after tag insertion.