Incompatible introductions: Otter predation compromises the introduction of razorback suckers into the wild

Reintroductions of endangered native fishes are critical to their survival.  Suitable habitats for large fish like razorback suckers are rare because they require large, slow flowing rivers with high sediment loads.  Exotic piscivores and the lack of large unimpeded rivers compromise introductions.  Managers are introducing razorbacks into fast streams with less predation pressure so that fish will grow larger before entering higher order streams with large piscivores.  Pond-reared razorbacks however, tend to migrate downstream in high flow.  In Fossil Creek, AZ we tested if exercise conditioned fish maintain their positions upstream and if predation rates by reintroduced otters undermine the success of introduction.  242 razorbacks were held in ponds and exercised in circular channels with water velocity approximating 30cm/sec.  A control group containing 242 razorbacks was maintained in no flow conditions.  Laboratory trials showed that exercised fish had higher swimming stamina than controls.  In the river, most fish migrated downstream but exercised fish migrated more slowly.  Nearly 10% of fish tags were found in otter scat within one month of introduction.  Hoop net surveys 1 month after introduction captured no razorbacks.  Sixty six % of tags recovered in scat were from control fish indicating that exercising may reduce predation rates.