Rearing in a distorted magnetic field disrupts the ‘map sense’ of juvenile steelhead trout

To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by the Royal Society. The published article can be found at: http://rsbl.royalsocietypublishing.org/.We used simulated magnetic displacements to test orientation preferences of\ud juvenile steelhead trout (Oncorhynchus mykiss) exposed to magnetic fields\ud existing at the northernmost and southernmost boundaries of their oceanic\ud range. Fish reared in natural magnetic conditions distinguished between\ud these two fields by orienting in opposite directions, with headings that\ud would lead fish towards marine foraging grounds. However, fish reared in\ud a spatially distorted magnetic field failed to distinguish between the\ud experimental fields and were randomly oriented. The non-uniform field in\ud which fish were reared is probably typical of fields that many hatchery fish\ud encounter due to magnetic distortions associated with the infrastructure\ud of aquaculture. Given that the reduced navigational abilities we observed\ud could negatively influence marine survival, homing ability and hatchery efficiency,\ud we recommend further study on the implications of rearing salmonids\ud in unnatural magnetic fields