Refinement of acoustic-tagging protocol for twaite shad Alosa fallax (Lacépède), a species sensitive to handling and sedation.

Abstract

Telemetry investigations to gather essential information about fish migrations are reliant on the behaviour, condition and survival of the animals being unaltered by the tagging procedure. Twaite shad (Alosa fallax Lacépède; 'shad’) is a threatened clupeid fish for which there is a considerable knowledge gap on their anadromous movements. They are also reported to be sensitive to handling and anaesthesia, resulting in practical difficulties in tag implantation; previous investigations externally attached tags without sedation. The aim of this study was to incrementally refine the acoustic-tagging protocol for shad via application of a previously un-tried anaesthetic (i.e. tricaine methanesulphonate (MS-222)) and by surgical implantation of the tag in the peritoneal cavity. All captured shad (n = 25) survived handling, anaesthesia and tagging, and were detected moving upstream after release. Surgically implantation (n = 5) was significantly faster than externally mounting the tag (n = 20) and time to recover was similar. Total upstream movement, total movement, residence time in receiver array and speed of upstream movement were statistically similar for externally and internally tagged fish. Post-spawning, a large proportion (68%) of tagged fish returned to the estuary, downstream of the receiver array. Internal tagging under anaesthesia is recommended for studying anadromous movements of shad, given welfare benefits during surgery and once at liberty, thus increasing the likelihood of tagged fish performing natural behaviours. Further, implantation of tags programmed to last many years enables multiple spawning migrations by the same individuals to be studied, which would lead to substantial advances in ecological knowledge and potentially reduce the number of fish tagged.