Evaluation of the effects of fine sediment inputs from stream culverts on brown trout egg survival through field and laboratory assessments

Laboratory and field assessments were used to determine whether the construction of culverts affects brown trout (Salmo trutta L.) egg survival through the introduction of elevated sediment levels. In the laboratory, survival was closely related to fine sediment. Survival to hatching was reduced to 28% for eggs incubating in medium fine sediment treatment (20%), and no eggs survived to hatching in high fine sediment (40%). An exposure index was developed to investigate the effect on survival of increased exposure time of eggs to sediment. This index, suggests that exposure time to sediment was negatively related to survival and confirmed the importance of incorporating exposure time in future studies. In the field, no significant difference was detected in egg survival between the control sites (upstream of culverts) and test sites (downstream of culverts), and a similar result was found for total fine sediment. The assessment did highlight that variation in culvert location and design can influence sediment input into rivers, and the exposure index again confirmed that exposure time to sediment is important in the field.