The Effects of a Surgically Implanted Microacoustic Tag on Growth and Survival in Subyearling Fall Chinook Salmon

Abstract

The objective of this study was to evaluate a newly miniaturized prototype of an implantable acoustic tag for use in subyearling hatchery Chinook salmon Oncorhynchus tshawytscha. In 2003, when the study was conducted, the relatively large size of most acoustic tags limited their use in juvenile fish. We evaluated this miniaturized prototype tag (21 × 7 × 6 mm, 0.9 g in air) for effects on growth, survival, and tag retention. All fish were passive integrated transponder (PIT) tagged in accordance with the proposed practical application in which PIT-tagged fish from known sources were separated from the general migrating population. The PIT tags also permitted tracking of individual fish growth in relation to treatment. We compared growth and acoustic tag retention over 30 d among tagged, sham-tagged, and control fish. Ratio of tag weight to body weight ranged from 2.6% to 5.9% at tagging. The acoustic tag significantly affected growth (P = 0.001 for both length and weight differences), but no fish died as a result of the tagging. Partial to complete tag expulsion was noted in 37% of the tagged fish after 30 d. Our study showed that impeded growth and tag expulsion may affect the successful use of this tag size in juvenile Chinook salmon. This evaluation led to physical tag modifications that improved biological acceptance by the fish, thus facilitating the tag's use in applied studies. Implanted devices should be evaluated before use to ensure compatibility and to avoid data misinterpretations due to their effects on the fish.