Tolerable ranges of fluid shear for early life-stage fishes: implications for safe fish passage at hydropower and irrigation infrastructure

Egg and larval fish drifting downstream are likely to encounter river infrastructure leading to mortality. Elevated fluid shear is one likely cause. To confirm this and determine tolerable strain rates resulting from fluid shear, egg and larvae of three Australian species were exposed to a high-velocity, submerged jet in a laboratory flume. Mortality was modelled over a broad range of strain rates, allowing critical thresholds to be estimated. Eggs were very susceptible to mortality at low strain rates and 100% of golden and silver perch died once strain rate exceeded 629 and 148s–1 respectively. Larvae were less vulnerable than eggs, but mortality increased at higher strain rates and at younger ages. Most ages of larvae will be protected if strain rate does not exceed 600s–1, although a lower guideline of less than 400s–1 may be needed in areas where very early stage Murray cod larvae drift. Golden perch and silver perch were not susceptible to shear once maturity reached ~25 days post-hatch (nearing juvenile metamorphosis). The thresholds described here will prove useful when refining design and operational guidelines for hydropower and irrigation infrastructure to improve fish survival.