Reproductive Development and Migration Behavior of Reconditioned Steelhead Kelts in the Yakima River, Washington

Starting in 1999, efforts to restore wild steelhead in the Yakima River have included long term captive reconditioning of post-spawn females (kelts). Downstream migrating kelts are collected in late spring, tagged with passive integrated transponder (PIT) tags, placed in tanks, and fed over the summer. During the fall upstream migration period the reconditioned kelts are released back into the river. However, little is known about the reproductive success of these fish. We sampled blood and non-lethally measured muscle lipid levels in fish released in 2009 and 2010. Plasma levels of vitellogenin (VTG), an indicator of ovarian development, were measured and post-release upstream movements were monitored via PIT tag detections at Prosser Dam. In both years, plasma VTG levels at release were bi-modally distributed with median values of 14.2 x10^-6 mg VTG/mL and 2.9 mg VTG/mL for the low and high modes, respectively. We compared VTG and ovary necropsy data from five mortalities at the time of release in 2010 to categorize release fish from both years into maturing (≥1 mg VTG/mL; ovaries with large follicles) and non-maturing (<1 mg VTG/mL; ovaries with small follicles) groups. In 2009, 55% (42 of 76) of sampled kelts were maturing, and of these 36% (15) were detected moving upstream. No non-maturing fish were detected moving upstream. In 2010, 25% (25 of 101) of sampled kelts were maturing. In 2009, muscle lipid levels measured at the time of release were higher in fish detected moving upriver (4.9 ± 0.4%; n=29) than fish not detected (3.4 ± 0.2%; n=96). Furthermore, there were four fish released in 2009 that were recaptured in the spring of 2010 that had the highest muscle lipid levels (7.7 ± 0.9%; n=4) measured at the 2009 release. These data indicate that over the past two years of the Yakima River kelt reconditioning program approximately 38% of the fish had levels of VTG indicative of advancing ovarian development at the time of release. The remaining kelts had much lower VTG levels, suggesting that these fish may be skip spawners. Data from the 2009 release suggest that only maturing fish migrated upriver and those with higher lipid levels were more likely to show migratory behavior consistent with spawning. Important questions regarding the management of reconditioned kelts include 1) what is the fate of maturing fish not detected moving upstream after release and 2) what is the best strategy for handling non-maturing reconditioned kelts?