Oral Presentation Australian Society for Fish Biology Conference 2017

Skipped spawning by diadromous fishes drives the direction and extent of material subsidies across marine-freshwater ecotones (#76)

David Crook 1 , Gregoire Saboret 1 2 , Duncan Buckle 1 , Alison King 1 , Michael Douglas 3
  1. Charles Darwin University, Darwin, NT, Australia
  2. Master Biosciences, ENS Lyon, Lyon, France
  3. School of Earth and Environment, The University of Western Australia, Crawley, WA, Australia

The large-scale migration of diadromous fishes transports assimilated nutrients and energy across ecotones, providing material subsidies that support critical ecosystem processes. The most famous example of this is the migration of anadromous Pacific salmon (Oncorhynchus spp.). After several years living at sea, adult salmon migrate upstream into rivers to spawn. They die soon after spawning (i.e., they are semelparous) and, thereby, deliver an annual pulse of marine-derived nutrients and energy into freshwater and terrestrial food webs.

Although the anadromous, semelparous life histories of salmon dominate the food web subsidy literature, this migratory mode is by no means characteristic of all diadromous fishes. In fact, there is a range of diadromous migration strategies, including catadromy (growth in freshwater, spawning at sea) and amphidromy (juvenile growth at sea, spawning and maturation in freshwater). Within these broad categories, there is inter-specific variation in migratory strategies and individual variation in movement behaviour within species (i.e., partial migration, skipped spawning, etc.). The influence of inter- and intra-specific life history variation in fishes on food web subsidies has not been studied in detail to date.

In this presentation, we use otolith chemistry, acoustic telemetry and length-at-age relationships to estimate material subsidies in the catadromous mullet Liza ordensis. We then extend our subsidy model to different diadromous migration strategies and manipulate life history variables, including growth rate, mortality rate, rate of skipped spawning and age at first migration, to examine their effects on the direction and extent of material subsidies. Our results show that individual variation in migration behaviour, especially skipped spawning, has a profound influence on nutrient and energy subsidies across marine-freshwater ecotones. Human disturbances that influence the expression of migratory behaviours are therefore likely to have major ramifications for aquatic food webs and the organisms they support.