Feasibility of Passive Integrated Transponder and Acoustic Tagging for Endangered Adult Delta Smelt

Conservation and recovery of endangered species requires timely and defensible data to predict their responses to management actions. In the Sacramento–San Joaquin Delta, the population of Delta Smelt Hypomesus transpacificus , a species of management concern, has declined to a record low. Alternative research strategies are now sought to determine the efficacy of management actions. In this study, we assessed the feasibility of tagging cultured adult Delta Smelt as a potential surrogate for wild fish in field experiments. Preliminary experiments determined that anesthesia of Delta Smelt in 35 mg/L AQUI-S 20E for 4 min best facilitated tagging. The 28-d survival of Delta Smelt (n = 39) intracoelomically injected with passive integrated transponder (PIT) tags (8.4 mm, 0.03 g) was high (95%) and did not differ from untagged control fish; tag retention was 97%. Survival of Delta Smelt with injected (n = 40) and surgically inserted (n = 40) dummy acoustic transmitters (15.0 mm, 0.22 g) was significantly lower than PIT-tagged and control fish, with only 60% surviving tag injection and 50% surviving surgical tag insertion. Surviving fish had high tag retention (injected: 95%; surgically inserted: 100%). Although not quantified, observational data suggested that the swimming ability of fish with acoustic tags was impaired. These results indicate that cultured Delta Smelt injected with PIT tags provide resource managers with a readily available wild surrogate to examine management actions in the delta. However, acoustic tags, which provide more detailed information on movement patterns, must be made smaller to reduce effects on survival before they can be used successfully in Delta Smelt. Logistic regression suggested that achievement of high survival (>90%) would require a tag mass: body mass ratio below 0.02. Received January 27, 2016; accepted May 25, 2016 Published online September 13, 2016