Does fine sediment constrain salmonid alevin development and survival?

We applied a randomized factorial design with three sedimentation treatments (high, low, and zero sediment addition) and two predation-risk levels (predator present or absent) to assess whether the survival and emergence of brown trout (Salm trutta) alevins were affected by sedimentation and (or) chemical cues from a predatory fish (burbot, Lota lota). In this laboratory experiment, survival was only related to the finest organic sediment fraction (<0.074 mm), which decreased embryo survival, although only constituting less than 1.5% of all sediments. Control fish tended to postpone emergence when exposed to predator odour, whereas fish in the high-sedimentation treatment showed no response to predators. Alevins that received high sedimentation had larger yolk sacs at emergence compared with control fish. Sedimentation may thus have serious fitness consequences on salmonids, as fry with larger yolk sacs are poor swimmers and therefore more vulnerable to predation or downstream displacement. Fine-sediment deposition from the catchment or stream banks may cause a serious threat to salmonid populations, and more effective erosion control is needed to reduce inputs of fine sediments to river habitats.