Returns of Hatchery Steelhead with Different Fin Clips and Coded Wire Tag Lengths

Left ventral (LV) fin clips have routinely been used in the Columbia River basin to visually identify the presence of a coded wire tag (CWT) in steelhead Oncorhynchus mykiss. Managers and researchers alike have expressed concern that the ventral fin clip may negatively affect survival. Adult returns from summer steelhead smolts released from Lyons Ferry Hatchery (LFH), Washington State, between 1996 and 1999 having combinations of adipose (AD) and LV fin clips and 1.1- or 1.6-mm-long CWTs were compared. The CWT loss rate calculated from release to adult recovery was 1.9% and the LV fin clip regeneration rate was 2.4%; neither of these rates influenced our recovery results. We found slight, nonsignificant differences in return rates between fish with AD fin clips and those with both AD and LV fin clips (ADLV) and between fish with 1.1-mm CWTs and those with 1.6-mm CWTs. Overall, fish with ADLV fin clips had LFH return rates that were 5% greater than those of fish with AD-only clips, and fish with 1.6-mm CWTs had LFH return rates that were 6% higher than those of fish with 1.1-mm CWTs. Increased straying because of the 1.6-mm CWT length was not evident, although there was likely sampling bias at other hatcheries or traps that did not conduct electronic CWT scans of fish that lacked LV clips. Two variables that may have influenced our results were examined, but neither was determined to be a factor in our results. Our study results suggest that a ventral fin clip or longer CWT does not impair adult returns (survival) of hatchery summer steelhead. Unfortunately, study limitations reduced our statistical power to definitively conclude that there was no significant difference in survival, and additional study may be necessary. However, our study provides sufficient information for fishery managers to consider use of the LV clip on hatchery steelhead as a visual cue for CWT recovery when electronic scanning of fish will be inconsistently used or is unavailable. Also, we suggest the use of 1.6-mm CWTs if electronic detection is to be the primary recovery method as it does not appear to affect survival in hatchery steelhead. We strongly caution managers to ensure that 100% electronic scanning of fish occurs throughout the region before foregoing standard LV fin clip marks on steelhead that contain CWTs.