Testing dissolvable sutures for the delayed release of external acoustic tags

Abstract Objective Recreational catch-and-release mortality (CRM) constitutes a substantial mortality source in many fisheries. While early estimation of CRM relied on direct observations (e.g., lab tanks, holding pens) that may bias estimates, acoustic telemetry can reduce bias by better emulating fishery practices. This also prioritizes fish welfare if external tags can be released once data acquisition has ended. Therefore, the objective of this study was to develop and test delayed-release, externally attached acoustic tags for CRM estimation and determine the effectiveness of our design in the field. Methods We tested the release timing of acoustic tags and dissolution rates (breaking strength) among suture materials (polyglactin [Vicryl] and polydioxanone [PDS], plain gut, chromic gut) and sizes (4/0, 2/0, and 0) at two water temperatures (15°C, 28°C) in the lab. We used V-13 dummy Innovasea transmitters with end caps attached to suspended tags via a suture. Additionally, using our trial-determined suture (Vicryl 0), we evaluated the breaking strength in 28°C to ensure that tags would remain attached for the duration of their battery life during summer field conditions. Finally, we implemented our delayed-release method in the field on Striped Bass Morone saxatilis and recorded the duration of tag detections and angler recaptures. Results The breaking force of sutures was significantly different, where the 28°C treatment showed lower breaking forces than the 15°C or control treatments after 70 d. Chromic gut and plain gut sutures had the fastest dissolution rates and lowest breaking forces, while PDS sutures did not exhibit any loss of strength. We chose Vicryl size 0 as our preferred suture given its strong initial tensile strength, which was retained through 3 weeks of warmwater exposure before declining significantly by its approximate failure point at 70 d. In the field, Striped Bass retained externally attached tags in this manner and were detected alive and moving for a mean ± SE of 65 ± 1 d, exceeding the predicted 57-d battery life. Tag retention was further confirmed by angler recaptures of fish with retained (n = 2) and absent acoustic tags (n = 3) at expected time frames. Conclusions The addition of a dissolvable suture loop to an established external acoustic tagging method allows the benefits of external acoustic tagging for CRM estimation, including speed, lack of anesthesia, and emulation of recreational fishing (i.e., no surgery), while alleviating the drawback of unnecessary tag burdens once data collection ceased. Still, suture materials and sizes should be tested on a case-by-case basis, ensuring that acoustic tags remain attached for the duration needed to meet their study objectives.