Study 11. Effects of Nanophyetus on the swimming performance and survival of steelhead smolts AND studies to understand and manage the Nanophyetus cercaria

Recent field surveillances indicated that outmigrating steelhead smolts in several south Puget Sound watersheds are infected with the digenean trematode Nanophyetus salmonicola at high prevalence and intensity (Chen et al Accepted). The apparent severity of these infections, especially in the Nisqually and Green / Duwamish Rivers, lead to the hypothesis that Nanophyetus may play a role as a proximate and / or ultimate factor contributing to the early seawater mortality of smolts after entering Puget Sound. This hypothesis was tested during 2016 using controlled laboratory and field based studies that were intended to investigate possible effects of Nanophyetus infection on:

1. the survival of steelhead smolts during their outmigration through Puget Sound,

2. the ability of steelhead smolts to survive transition from freshwater to seawater,

3. the swimming performance of infected steelhead smolts.