Oral Presentation International Conference on River Connectivity (Fish Passage 2018)

The migrations of amphidromous species: implications for fish passage and water infrastructure (#31)

Matt G. Jarvis 1 , Gerry Closs 1
  1. University of Otago, Dunedin, SOUTH ISLAND, New Zealand

Amphidromous species undertake a number of migrations throughout their life-history, migrating to sea immediately after hatching in freshwater, migrating back to freshwater after a pelagic larval period, and potentially undertaking adult spawning migrations. Amphidromous species are therefore likely to be highly susceptible to water infrastructure, having different migratory directions, objectives, and requirements at different life stages. We review the current state of knowledge on the migrations of amphidromous species, identifying the requirements for successful migrations, and potential threats during these migrations from water infrastructure associated with anthropogenic activities. Downstream spawning migrations were found to be common in numerous amphidromous taxa, and spawning migrations and the hatching of eggs are often associated with natural changes in flow regime, highlighting the need for bidirectional fish passage, and the potential for artificial flow alteration to negatively affect reproduction. Once hatched, larvae migrating downstream were found to be highly susceptible to numerous hazards associated with water infrastructure, including larval retention and starvation in freshwater, increased mortality due to expedited migration, entrainment and impingement at water intakes, and barotrauma and physical damage associated with weirs and turbines. Distinct patterns of larval drift (spatial and temporal) may provide opportunities to alleviate mortality during larval emigration. While in-stream barriers inhibit the upstream migrations of amphidromous postlarvae and juveniles, climbing abilities are common, allowing for creative solutions facilitating upstream migration. Overall, much of the focus on amphidromous fish passage has been placed on upstream migrating postlarvae and juveniles, while the requirements of migrating adults and larvae, which may be far more susceptible to water infrastructure, have largely been ignored. This life-stage bias represents a key research gap that must be addressed to safeguard amphidromous species in future.