Performance of subyearling fall Chinook salmon tagged with 8‐, 9‐, and 12‐mm passive integrated transponder tags in the Snake River

Inferences based on tagged individuals from a population are limited in part by the minimum size of fish that can be tagged. Smaller tags allow a greater proportion of a population to be represented by tagging and should reduce potential tag effects on fish performance. We evaluated different performance metrics of juvenile fall Chinook Salmon Oncorhynchus tshawytscha tagged with 8‐, 9‐, and 12‐mm PIT tags in the Snake River. We did not find evidence that posttagging mortality of 45–49‐mm‐FL fish tagged with 8‐mm tags was higher than the posttagging mortality of larger fish tagged with 9‐ and 12‐mm tags. The incisions of fish tagged with 8‐mm tags using 14‐guage needles healed faster than those of fish tagged with larger tags using 12‐guage needles. For individuals that received 8‐mm tags, growth in length and mass was higher for 45–49‐mm fish than for 50–59‐mm fish and 60‐mm and larger fish. Growth of the larger size‐classes (50–59 and ≥60 mm) was also generally higher for those tagged with 8‐mm tags compared to those tagged with 9‐ and 12‐mm tags, respectively. There were no strong relationships between tag burden (i.e., tag weight expressed as a percentage of fish weight) at the time of tagging and growth metrics for any tag size or fish size‐class. Releases made to compare the detection efficiency of the three tag types in the juvenile fish bypass at Lower Granite Dam, Washington, showed that 99–100% of all fish were detected. Survival of fish from rearing areas to Lower Granite Dam generally increased with fish size and varied by year, but there was no strong evidence of a tag size effect. The 8‐mm PIT tag allowed us to represent a larger portion (i.e., 6.2–24.1%) of the subyearling fall Chinook Salmon population in the Snake River without compromising fish performance or detectability at the dam.